Improving hydrodynamic injection in capillary electrophoresis by using the integral of pressure

A careful analysis of the typical devices and conditions used during hydrodynamic injection in capillary electrophoresis shows that the Hagen-Poiseuille model for the laminar flow is valid, even during the transitions of pressure. Therefore, the monitoring of pressure becomes a reliable approach to evaluate the effective injected volume, because the volume is proportional to the integral of pressure (IoP) over time. A piezoresistive sensor was used to monitor the air pressure at headspace of the sample vial. A set of 18 injections at 50 mbar and different times were used to evaluate the use of the normalization of the peak areas of the analytes by the IoP to compensate for imperfection during the injection. There was a significant decrease in relative standard deviation (RSD), and the proposed approach presented results similar to the use of internal standard. In addition, a microcontroller was used not only to monitor the pressure but also to command a peristaltic pump and a solenoid valve creating a system that dynamically controls the applied pressure and stops the injection when the desired value of IoP is reached. The system was used in a proof of concept in which different combinations of pressure and time were used: 10 mbar × 50 s, 25 mbar × 20 s, 50 mbar × 10 s, 125 mbar × 4 s, and 250 mbar × 2 s. Despite the constraints posed by the flowrates of the peristaltic pump and the solenoid valve, the microcontroller effectively conducted the injections across this extensive range of conditions, resulting in an IoP RSD of 2.7%.

Moxidectin is a candidate for use as an in vivo internal standard in pharmacokinetic studies, as demonstrated with use in simultaneous tissue cage and ultrafiltration fluid collection

In vivo ultrafiltration has been used in veterinary pharmacokinetics since the early 2000's as an improvement on the tissue cage model which enables sampling of fluids from extra-circulatory compartments. Variability in analyte recovery from ultrafiltration samples, due to membrane fouling or tissue inflammation, has been a concern for this technique. Internal standards may be used to scale or verify the unknown result, such as is common in analytical extractions and in vivo microdialysis. Eight merino sheep were implanted with subcutaneous tissue cages and 2 weeks prior to the initiation of the study the sheep were injected with 0.2 mg/kg moxidectin subcutaneously. On the day of the study ultrafiltration probes were inserted subcutaneously. At time zero 4 mg/kg of carprofen was injected intravenously. Plasma, tissue cage, and ultrafiltration samples were taken 30 min before and 0.5, 1, 2, 3, 4, 5, 7, 24, 36, 48, 72 h after dosing. Carprofen and moxidectin concentrations were measured by LC-MS/MS. Pharmacokinetic parameters were estimated using Monolix for both the carprofen concentrations and the moxidectin corrected carprofen concentrations. The ultrafiltration probes failed to consistently produce enough sample volume to analyse. Moxidectin concentrations in the plasma and tissue cage fluid were stable throughout the 72 h sampling window. Moxidectin proved to be suitable as an in vivo internal standard for pharmacokinetic research using, tissue cages, plasma sampling and ultrafiltration probes, but the application of ultrafiltration techniques requires refinement.

An inhibitor-monitorable single-tube duplex quantitative real-time PCR assay for the detection of Candidatus Liberibacter asiaticus

Huanglongbing (HLB) is a citrus infectious disease caused by Candidatus Liberibacters spp. Recently, it has begun to spread rapidly worldwide, causing significant losses to the citrus industry. Early diagnosis of HLB relies on quantitative real-time PCR assays. However, the PCR inhibitors found in the nucleic acid extracted from plant materials pose challenges for PCR assays because they may result in false-negative results. Internal standard (IS) can be introduced to establish a single-tube duplex PCR (STD-PCR) for monitoring the influence of the PCR-inhibitor, but it also brings the risk of false-negative results because the amplification of IS may compete with the target. To solve this problem, we proposed a mutation-enhanced single-tube duplex PCR (mSTD-PCR) containing IS with mutant-type primers. By introducing the 3'-terminal mutation in the primer of IS to weaken its amplification reaction and its inhibition of Candidatus Liberibacter asiaticus (CLas) detection, the sensitivity and quantitative accuracy of CLas detection will not be affected by IS. In evaluating the sensitivity of CLas detection using simulation samples, the mSTD-PCR showed consistent sensitivity at 25 copies/test compared with the single-plex CLas assay. The detection result of 30 leaves and 30 root samples showed that mSTD-PCR could recognize false-negative results caused by the PCR inhibitors and reduce workload by 48% compared with the single-plex CLas assay. Generally, the proposed mSTD-PCR provides a reliable, efficient, inhibitor-monitorable, and quantitative screening method for accurately controlling HLB and a universal method for establishing PCR assay for various pathogens.

Quantification of Oligonucleotides Using Tandem Mass Spectrometry with Isobaric Internal Standards

In recent years, oligonucleotides have become more important in research, drug approvals and medical therapies. Due to this growing interest in pharmaceutical applications, it is essential to develop reliable analytical methods for this substance class. In this work, we present a quantification method using liquid chromatography coupled with tandem mass spectrometry by applying an isobaric oligonucleotide standard. In addition to a proof of principle, we perform a method qualification to assess its readiness for validation according to ICH Q2 guidelines. In addition to good linearity, sensitivity, accuracy and recovery, the method showed no significant matrix effects. Furthermore, we demonstrated the application of the method by applying the quantification in a biological matrix, as well as an exemplary degradation of an oligonucleotide in bovine plasma.

A low-cost internal standard loader for solid-phase sorbing tools

Solid-phase sorption is widely used for the analysis of gaseous specimens as it allows at the same time to preconcentrate target analytes and store samples for relatively long periods. The addition of internal standards (ISs) in the analytical workflow can greatly reduce the variability of the analyses and improve the reliability of the protocols. In this work, we describe the development and testing of a portable system for the reliable production of gaseous mixture of8D-Toluene in a 1L Silonite canister as well as its reproducible loading into solid-phase sorbing tools as ISs. The portable system was tested using needle trap microextraction, solid-phase extraction, and thin-film microextraction techniques commonly employed for the analysis of gaseous samples. Even though our specific interest is in breath analysis, the system can also be used for the collection of any kind of gaseous specimen. A microcontroller allows the fine control of the sampling flow by a digital mass flow controller. Flow rate and sample volume could be set either through a rotary encoder mounted onto the control board or through a dedicated android app. The variability of the airflow is in the range 5-200 ml min-1and it is lower than 1%, whereas the variability of the IS (8D-Toluene) concentration dispensed over time by the loader measured by selected-ion flow-tube mass spectrometry (MS) is <3%. This combination resulted in intra- and inter-day precision of the amount loaded in the sorbent tools lower than 15%. No carry-over was detected in the loader after the delivery of the8D-Toluene measured by gas chromatography-MS. The8D-Toluene concentration in the canister was stable for up to three weeks at room temperature.

Determination of Response Factors for Analytes Detected during Migration Studies, Strategy and Internal Standard Selection for Risk Minimization

Migration studies are one of the few domains of pharmaceutical analysis employing wide-scope screening methodologies. The studies involve the detection of contaminants within pharmaceutical products that arise from the interaction between the formulation and materials. Requiring both qualitative and quantitative data, the studies are conducted using Liquid Chromatography or Gas Chromatography coupled to a mass spectrometer (LC-MS and GC-MS). While mass spectrometry allows wide-scope analyte detection and identification at the very low Analytical Evaluation Threshold (AET) levels used in these studies, MS detectors are far from "universal response" detectors. Regulation brings the application of uncertainty factors into the picture to limit the risk of potential analytes detected escaping report and further evaluation; however, whether the application of a default value can cover any or all relevant applications is still debatable. The current study evaluated the response of species usually detected in migration studies, generating a suitable representative sample, analyzing said species, and creating a strategy and evaluation mechanism for acceptable classification of the detected species. Incorporating novel methodologies, i.e., Design of Experiments (DoE) for Design Space generation, the LC-MS-based methodology is also evaluated for its robustness in changes performed.

An Approach Based on an Increased Bandpass for Enabling the Use of Internal Standards in Single Particle ICP-MS: Application to AuNPs Characterization

This paper proposes a novel approach to implement an internal standard (IS) correction in single particle inductively coupled plasma mass spectrometry (SP ICP-MS), as exemplified for the characterization of Au nanoparticles (NPs) in complex matrices. This approach is based on the use of the mass spectrometer (quadrupole) in bandpass mode, enhancing the sensitivity for the monitoring of AuNPs while also allowing for the detection of PtNPs in the same measurement run, such that they can serve as an internal standard. The performance of the method developed was proved for three different matrices: pure water, a 5 g L^-1 NaCl water solution, and another water solution containing 2.5% (m/v) tetramethylammonium hydroxide (TMAH)/0.1% Triton X-100. It was observed that matrix-effects impacted both the sensitivity of the NPs and their transport efficiencies. To circumvent this problem, two methods were used to determine the TE: the particle size method for sizing and the dynamic mass flow method for the determination of the particle number concentration (PNC). This fact, together with the use of the IS, enabled us to attain accurate results in all cases, both for sizing and for the PNC determination. Additionally, the use of the bandpass mode provides additional flexibility for this characterization, as it is possible to easily tune the sensitivity achieved for each NP type to ensure that their distributions are sufficiently resolved.

The use of matrix-assisted laser desorption/ionization mass spectrometry in enzyme activity assays and its position in the context of other available methods

Activity assays are indispensable for studying biochemical properties of enzymes. The purposes of measuring activity are wide ranging from a simple detection of the presence of an enzyme to kinetic experiments evaluating the substrate specificity, reaction mechanisms, and susceptibility to inhibitors. Common activity assay methods include spectroscopy, electrochemical sensors, or liquid chromatography coupled with various detection techniques. This review focuses on the use of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) as a growing and modern alternative, which offers high speed of analysis, sensitivity, versatility, possibility of automation, and cost-effectiveness. It may reveal reaction intermediates, side products or measure more enzymes at once. The addition of an internal standard or calculating the ratios of the substrate and product peak intensities and areas overcome the inherent inhomogeneous distribution of analyte and matrix in the sample spot, which otherwise results in a poor reproducibility. Examples of the application of MALDI-TOF MS for assaying hydrolases (including peptidases and β-lactamases for antibiotic resistance tests) and other enzymes are provided. Concluding remarks summarize advantages and challenges coming from the present experience, and draw future perspectives such as a screening of large libraries of chemical compounds for their substrate or inhibitory properties towards enzymes.

Dual Function of 4-Aminothiophene in Surface-Enhanced Raman Scattering Application as an Internal Standard and Adsorbent for Controlling Au Nanocrystal Morphology

The sensitivity and quantitative accuracy of surface-enhanced Raman scattering (SERS) are the main factors that restrict its application. Here, novel Au nanoscale convex polyhedrons (Au NCPs) were designed and fabricated to solve these problems via an embedded standard, including eight pods and six small protrusions. Spherical Au seeds regrew into different sizes of Au NCPs with a face-centered cubic structure. This morphology is due to the dual mechanism of the 4-aminothiophene (4-ATP) molecule that serves as an internal standard and a surface ligand regulator combined with the regulatory role of hexadecyl trimethyl ammonium chloride. The results show that Au NCPs were enclosed by high-index {12 9 1} facets, which greatly improved the local plasma resonance and reduced the lowest SERS detectable concentration of pyrene in standard seawater to 0.5 nM. An effective reference was produced by embedding 4-ATP with a relative standard deviation value less than 2.97% (in the same batch) and 3.92% (between different batches). Our research offers a new strategy for morphological regulation of metal nanocrystals, which is useful for the preparation of highly sensitive SERS substrates and trace analysis.

Synthesis and characterization of d5 -barbarin for use in barbarin-related research

Based on structural similarities and equine administration experiments, Barbarin, 5-phenyl-2-oxazolidinethione from Brassicaceae plants, is a possible source of equine urinary identifications of aminorex, (R,S)-5-phenyl-4,5-dihydro-1,3-oxazol-2-amine, an amphetamine-related US Drug Enforcement Administration (DEA) controlled substance considered illegal in sport horses. We now report the synthesis and certification of d₅ -barbarin to facilitate research on the relationship between plant barbarin and such aminorex identifications. D₅ -barbarin synthesis commenced with production of d₅ -2-oxo-2-phenylacetaldehyde oxime (d₅ -oxime) from d₅ -acetophenone via butylnitrite in an ethoxide/ethanol solution. This d₅ -oxime was then reduced with lithium aluminum hydride (LiAlH₄ ) to produce the corresponding d₅ -2-amino-1-phenylethan-1-ol (d₅ -phenylethanolamine). Final ring closure of the d₅ -phenylethanolamine was performed by the addition of carbon disulfide (CS₂ ) with pyridine. The reaction product was purified by recrystallization and presented as a stable white crystalline powder. Proton NMR spectroscopy revealed a triplet at 5.88 ppm for one proton, a double doublet at 3.71 ppm for one proton, and double doublet at 4.11 ppm for one proton, confirming d₅ -barbarin as the product. Further characterization by high resolution mass spectrometry supports the successful synthesis of d₅ -barbarin. Purity of the recrystallized product was ascertained by High Performance Liquid Chromatography (HPLC) to be greater than 98%. Together, we have developed the synthesis and full characterization of d₅ -barbarin for use as an internal standard in barbarin-related and equine forensic research.

Eco-Efficient Quantification of Glucosinolates in Camelina Seed, Oil, and Defatted Meal: Optimization, Development, and Validation of a UPLC-DAD Method

Camelina sativa (camelina) seed, oil, and defatted meal are widely used for food, animal feed, and other purposes. The accurate quantification of camelina glucosinolates is critical as their functionalities are highly dose-dependent. The classic quantification of glucosinolates in camelina products involves tedious desulfation steps, toxic reagents, and a lengthy instrument time because glucosinolates are easy to degrade and subject to interference in the liquid chromatography. Thus, we developed and validated an eco-efficient UPLC-DAD method for determining glucoarabin (GS9), glucocamelinin (GS10), and homoglucocamelinin (GS11) in camelina seed, oil, and defatted meal. Glucosinolates were extracted using 80% cold methanol to denature myrosinase, and were separated by an HSS T3 column without desulfation. Glucotropaeolin was used as an internal standard to track analyte degradation and loss during sample preparation. The method has shown high precision (relative standard deviations ranging from 4.12% to 6.54%) and accuracy (>94.4% spike recovery) for GS9-11, and all validation parameters passed the industry-consensus AOAC Appendix F criteria. To our best knowledge, this is the first eco-efficient and low-cost analytical method that is validated against strict AOAC criteria for the quantification of intact camelina glucosinolates. The method is suitable to be adopted as a new industrial testing standard to assist in the quality control of camelina products.

A Molecular Lateral Flow Assay for SARS-CoV-2 Quantitative Detection

Since the onset of the SARS-CoV-2 pandemic, several COVID-19 detection methods, both commercially available and in the lab, have been developed using different biomolecules as analytes and different detection and sampling methods with high analytical performance. Developing novel COVID-19 detection assays is an exciting research field, as rapid accurate diagnosis is a valuable tool to control the current pandemic, and also because the acquired knowledge can be deployed for facing future infectious outbreaks. We here developed a novel gold-nanoparticle-based nucleic acid lateral flow assay for the rapid, visual, and quantitative detection of SARS-CoV-2. Our method was based on the use of a DNA internal standard (competitor) for quantification and involved RT-PCR, the hybridization of biotinylated PCR products to specific oligonucleotide probes, and detection with a dual lateral flow assay using gold nanoparticles conjugated to an anti-biotin antibody as reporters. The developed test allowed for rapid detection by the naked eye and the simultaneous quantification of SARS-CoV-2 in nasopharyngeal swabs with high specificity, detectability, and repeatability. This novel molecular strip test for COVID-19 detection represents a simple, cost-effective, and accurate rapid test that is very promising to be used as a future diagnostic tool.

An Interlaboratory Comparison Study of Regulated and Emerging Mycotoxins Using Liquid Chromatography Mass Spectrometry: Challenges and Future Directions of Routine Multi-Mycotoxin Analysis including Emerging Mycotoxins

The present interlaboratory comparison study involved nine laboratories located throughout the world that tested for 24 regulated and non-regulated mycotoxins by applying their in-house LC-MS/MS multi-toxin method to 10 individual lots of 4 matrix commodities, including complex chicken and swine feed, soy and corn gluten. In total, more than 6000 data points were collected and analyzed statistically by calculating a consensus value in combination with a target standard deviation following a modified Horwitz equation. The performance of each participant was evaluated by a z-score assessment with a satisfying range of ±2, leading to an overall success rate of 70% for all tested compounds. Equal performance for both regulated and emerging mycotoxins indicates that participating routine laboratories have successfully expanded their analytical portfolio in view of potentially new regulations. In addition, the study design proved to be fit for the purpose of providing future certified reference materials, which surpass current analyte matrix combinations and exceed the typical scope of the regulatory framework.

Development of internal standard for lipoprotein subclass analysis using dual detection gel-permeation high-performance liquid chromatography system

The LipoSEARCH® System is an innovative lipoprotein class analysis method based on gel-permeation high-performance liquid chromatography (HPLC). This system uses a gel permeation column to separate the major lipoprotein subclasses (chylomicron, very low-density lipoprotein, low-density lipoprotein, and high-density lipoprotein) in serum according to particle size and splits them into two pathways to measure total cholesterol (TC; esterified + unesterified cholesterol) and triglyceride (TG) concentrations simultaneously to obtain chromatograms for each.

These chromatograms were analyzed based on the results of the calibration serum by fitting Gaussian curves to profile the 20 lipoprotein subclasses defined in detail. An important assumption of this HPLC system is its simultaneous detection of two pathways to guarantee the accuracy of each analysis. Therefore, in the present study, we investigated the development of an internal standard that can guarantee the simultaneous detection of this system by adding a pigment to the serum. We focused on quinone pigments with absorption at 550 nm, which is the wavelength used for the enzymatic assay of TC and TG concentrations in the system. As a result, we succeeded in producing overlapping pigment peaks that appeared after the analytical chromatograms in two pathways. It is also suggested that the pigment solution as an internal standard is stable in freezing storage and has little effect on the analysis. The developed internal standard is expected to contribute to the accuracy assurance of lipoprotein analysis by this dual-detection HPLC system.

Enantiomeric separation of oxomemazine in rabbit plasma by ultra-fast LC and application in a stereoselective pharmacokinetic study

Aim: Ultra-fast LC was used to establish a new bioanalytical method for enantiomeric separation of oxomemazine. Methods: The proposed study was carried out using the ultra-fast LC technique with an amylose chiral column. The bioanalytical approach was used in rabbit plasma following US FDA regulations and then extended to oxomemazine enantiomeric separation using metronidazole as the internal standard. Results: The retention times of (R)-oxomemazine, (S)-oxomemazine and the internal standard were found to be 9.511, 10.712 and 6.503 min, respectively. Within-run and between-run precision (percent relative standard deviation) was found to be in the range of 0.018-0.102% for (R)-oxomemazine and 0.028-0.675% for (S)-oxomemazine, whereas accuracy (%) was found to be in the range of 95.971-99.720% for (R)-oxomemazine and 97.199-103.921% for (S)-oxomemazine. Conclusion: The findings revealed that stereospecific distribution of oxomemazine enantiomers does not change significantly.

An Improved Synthesis of Glucuronide Metabolites of Hindered Phenolic Xenoestrogens

AIM AND OBJECTIVE

The syntheses of glucuronide metabolites of phenolic xenoestrogens triclosan and 2-phenylphenol, namely triclosan-O-glucuronide (TCS-G; 1), and 2-phenylphenol-O-glucuronide (OPP-G; 2), were achieved for use as analytical standards.

METHODS

Under classical conditions previously reported for glucuronide synthesis, the final basic hydrolysis of the peracylated ester intermediate leading to the free glucuronides is often a limiting step. Indeed, the presence of contaminating by-products resulting from ester elimination has often been observed during this step. This is particularly relevant when the sugar unit is close to a crowded environment as for triclosan and 2-phenylphenol.

RESULTS

To circumvent these problems, we proposed mild conditions for the deprotection of peracetylated glucuronate intermediates.

CONCLUSION

A new methodology using a key imidate following a two-step saponification protocol for acetates and methyl ester hydrolysis was successfully applied to the preparation of TCS-d3 (1) and OPP-G (2) as well as deuterated isotopomers TCS-d3-G (1-d3) and OPP-d5-G (2-d5).

An Endoscope-like SERS Probe Based on the Focusing Effect of Silica Nanospheres for Tyrosine and Urea Detection in Sweat

In this work, we developed a new type of SERS probe, which was composed of glass-SiO₂-Au@MBN@Ag nanoparticles (NPs) three-dimensional Surface-enhanced Raman spectroscopy (SERS) substrate. When the laser passed through the quartz glass sheet, on the one hand, the SiO₂ NPs supporting the Au@MBN@Ag NPs increase the roughness of the substrate surface, resulting in a large number of hot spots among nanoparticles. On the other hand, based on the focusing effect of silicon dioxide nanospheres, the laser can better focus on the surface of nanoparticles in the inverted SERS probe, thus showing better SERS enhancement. Furthermore, the Au@MBN@Ag NPs core-shell structure was used with 4-mercaptobenzoonitrile (MBN) as an internal standard molecule, and the quantitative determination of tyrosine and urea was realized by internal standard correction method. The standard working curves of the two had good linear correlation with R² above 0.9555. The detection limits of tyrosine and urea were in the range of 2.85 × 10⁻¹⁰ M~7.54 × 10⁻⁶ M, which confirms that this design can be used for quantitative and specific detection of biological molecules, demonstrating great practical significance for the research of diseases such as skin lesions and endocrine disorders.

Quantitative subcellular acyl-CoA analysis reveals distinct nuclear metabolism and isoleucine-dependent histone propionylation

Quantitative subcellular metabolomic measurements can explain the roles of metabolites in cellular processes but are subject to multiple confounding factors. We developed stable isotope labeling of essential nutrients in cell culture-subcellular fractionation (SILEC-SF), which uses isotope-labeled internal standard controls that are present throughout fractionation and processing to quantify acyl-coenzyme A (acyl-CoA) thioesters in subcellular compartments by liquid chromatography-mass spectrometry. We tested SILEC-SF in a range of sample types and examined the compartmentalized responses to oxygen tension, cellular differentiation, and nutrient availability. Application of SILEC-SF to the challenging analysis of the nuclear compartment revealed a nuclear acyl-CoA profile distinct from that of the cytosol, with notable nuclear enrichment of propionyl-CoA. Using isotope tracing, we identified the branched chain amino acid isoleucine as a major metabolic source of nuclear propionyl-CoA and histone propionylation, thus revealing a new mechanism of crosstalk between metabolism and the epigenome.

Introduction of a PEGylated EPO conjugate as internal standard for EPO analysis in doping controls

Immunopurification of doping control samples is a mandatory necessity in erythropoietin (EPO) analysis during a confirmation procedure; moreover, it has become common practice to also immunopurify samples for the initial testing procedure. Typically used materials (e.g., Stemcell purification plate and MAIIA purification kit) rely on anti-EPO antibodies for purification. Also, the detection of EPO after electrophoretic separation and western blotting is based on a monoclonal anti-EPO antibody, clone AE7A5, directed against a 26 amino acid sequence of the N-terminal region of human EPO. While the electrophoretic separation and blot transfer efficiency can be monitored with reference standards and quality control samples, it is presently not possible to monitor the functionality of the entire sample preparation procedure. The reliance on antibodies for both purification and detection has complicated the implementation of an internal standard (ISTD). In this study, customized EPO-polyethylene glycol (PEG) conjugates were synthesized as potential ISTDs and assessed as to their compatibility with existing sample preparation procedures for urine and blood sample analysis using the most common immunopurification techniques. Moreover, probing for the impact of the ISTD on sodium N-lauroylsarcosinate ("sarcosyl") polyacrylamide gel electrophoresis (SAR-PAGE)-based EPO analysis concerning potential interference with target analytes was conducted. The presented data demonstrate that a 12-kDa PEG residue attached to human EPO represents a particularly useful construct to serve as ISTD for erythropoietin-receptor agonist (ERA) analysis. The conjugate is applicable to both urine and blood testing using the commonly employed purification techniques, supporting and improving result interpretations especially concerning specimens where the natural abundance of human EPO is low.

Internal Standardization: Is It Necessary?

The aim of the work was to prepare a simple but reliable HPLC-UV method for the routine monitoring of mycophenolic acid (MPA). Sample preparation was based on plasma protein precipitation with acetonitrile. The isocratic separation of MPA and internal standard (IS) fenbufen was made on Supelcosil LC-CN column (150 × 4.6 mm, 5 µm) using a mobile phase: CH₃CN:H₂O:0.5M KH₂PO₄:H₃PO₄ (260:700:40:0.4, v/v). UV detection was set at 305 nm. The calibration covered the MPA concentration range: 0.1–40 µg/mL. The precision was satisfactory with RSD of 0.97–7.06% for intra-assay and of 1.92–5.15% for inter-assay. The inaccuracy was found between −5.72% and +2.96% (+15.40% at LLOQ) and between −8.82% and +5.31% (+19.00% at LLOQ) for intra- and inter-assay, respectively, fulfilling acceptance criteria. After a two-year period of successful application, the presented method has been retrospectively calibrated using the raw data disregarding the IS in the calculations. The validation and stability parameters were similar for both calculation methods. MPA concentrations were recalculated and compared in 1187 consecutive routine therapeutic drug monitoring (TDM) trough plasma samples from mycophenolate-treated patients. A high agreement (r² = 0.9931, p < 0.0001) of the results was found. A Bland–Altman test revealed a mean bias of −0.011 μg/mL (95% CI: −0.017; −0.005) comprising −0.14% (95% Cl: −0.39; +0.11), whereas the Passing–Bablok regression was y = 0.986x + 0.014. The presented method can be recommended as an attractive analytical tool for medical (hospital) laboratories equipped with solely basic HPLC apparatus. The procedure can be further simplified by disapplying an internal standard while maintaining appropriate precision and accuracy of measurements.

Influence of isotopically labeled internal standards on quantification of serum/plasma 17α-hydroxyprogesterone (17OHP) by liquid chromatography mass spectrometry

Objectives Our recent survey of 44 mass spectrometry laboratories across 17 countries identified variation in internal standard (IS) choice for the measurement of serum/plasma 17α-hydroxyprogesterone (17OHP) by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The choice of IS may contribute to inter-method variations. This study evaluated the effect of two common isotopically labeled IS on the quantification of 17OHP by LC-MS/MS. Methods Three collaborating LC-MS/MS laboratories from Asia, Europe and Australia, who routinely measure serum 17OHP, compared two IS, (1) IsoSciences carbon-13 labeled 17OHP-[2,3,4-13C3], and (2) IsoSciences deuterated 17OHP-[2,2,4,6,6,21,21,21-2H]. This was performed as part of their routine patient runs using their respective laboratory standard operating procedure. Results The three laboratories measured 99, 89, 95 independent samples, respectively (up to 100 nmol/L) using the 13C- and 2H-labeled IS. The slopes of the Passing-Bablok regression ranged 0.98-1.00 (all 95% confidence interval [CI] estimates included the line of identity), and intercept of <0.1 nmol/L. Average percentage differences of -0.04% to -5.4% were observed between the two IS materials, which were less than the optimal bias specification of 7% determined by biological variation, indicating no clinically significant difference. The results of 12 Royal College of Pathologists of Australasia Quality Assurance Programs (RCPAQAP) proficiency samples (1-40 nmol/L) measured by the laboratories were all within the RCPAQAP analytical performance specifications for both IS. Conclusions Overall, the comparison between the results of 13C- and 2H-labeled IS for 17OHP showed good agreement, and show no clinically significant bias when incorporated into the LC-MS/MS methods employed in the collaborating laboratories.

Development of an LC-MS/MS Method for Measurement of Irinotecan and Its Major Metabolites in Plasma: Technical Considerations

OBJECTIVE

Irinotecan (CPT-11) is an important drug used in the treatment of several solid tumor types. To minimize its toxicity, therapeutic drug monitoring of CPT-11 and its major metabolites (SN-38, SN-38-glucuronide [SN-38G], and APC) has been proposed. We aimed to develop a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the quantification of CPT-11 and its major metabolites in plasma.

METHODS

Specimen preparation consisted of protein precipitation, evaporation, and reconstitution. Analyses were performed on a C18 column using reverse-phase gradient elution. Electrospray ionization and multiple reaction monitoring in positive mode were used for MS. The following heavy isotope-labeled internal standards were used: CPT-11 D10, SN-38 D3, SN-38G D3, and APC D3.

RESULTS

We found that CPT-11, SN-38G, and APC eluted at ~4.6 to 4.7 minutes, and SN-38 eluted at ~5.1 to 5.2 minutes. A second peak for SN-38 was detected at ~4.6 to 4.7 minutes. Given that the structure of SN-38 is found in CPT-11, SN-38G, and APC, and in the CPT-11 D10 used here, in-source fragmentation was the likely cause. In addition, we found that a low-level SN-38 impurity was present in CPT-11 D10 and to a lesser extent in SN-38 D3.

CONCLUSION

When developing methods for CPT-11 and its metabolites, it is important to consider the effects of in-source fragmentation and the choice of internal standards.

Characterizing Microbiomes via Sequencing of Marker Loci: Techniques To Improve Throughput, Account for Cross-Contamination, and Reduce Cost

New approaches to characterizing microbiomes via high-throughput sequencing provide impressive gains in efficiency and cost reduction compared to approaches that were standard just a few years ago. However, the speed of method development has been such that staying abreast of the latest technological advances is challenging. Moreover, shifting laboratory protocols to include new methods can be expensive and time consuming. To facilitate adoption of new techniques, we provide a guide and review of recent advances that are relevant for single-locus sequence-based study of microbiomes—from extraction to library preparation—including a primer regarding the use of liquid-handling automation in small-scale academic settings. Additionally, we describe several amendments to published techniques to improve throughput, track contamination, and reduce cost. Notably, we suggest adding synthetic DNA molecules to each sample during nucleic acid extraction, thus providing a method of documenting incidences of cross-contamination. We also describe a dual-indexing scheme for Illumina sequencers that allows multiplexing of many thousands of samples with minimal PhiX input. Collectively, the techniques that we describe demonstrate that laboratory technology need not impose strict limitations on the scale of molecular microbial ecology studies.

IMPORTANCE New methods to characterize microbiomes reduce technology-imposed limitations to study design, but many new approaches have not been widely adopted. Here, we present techniques to increase throughput and reduce contamination alongside a thorough review of current best practices.

Screening and diagnosis of colorectal cancer and advanced adenoma by Bionic Glycome method and machine learning

Colorectal cancer (CRC), one of the major health problems worldwide, mostly develops from colorectal adenomas. Advanced adenomas are generally considered as precancerous lesions and patients are recommended to remove the adenomas. Screening for colorectal cancer is usually performed by fecal tests (FOBT or FIT) and colonoscopy, however, their benefits are limited by uptake and adherence. Most CRC develops from colorectal advanced adenomas, but there is currently a lack of effective noninvasive screening method for advanced adenomas. N-glycans in human serum hold the great potentials as biomarker for diagnosis of human cancers. Our aim was to discover blood-based markers for screening and diagnosis of advanced adenomas and CRC, and to ascertain their efficiency in classifying healthy controls, patients with advanced adenomas and CRC by incorporating machine learning techniques with reliable and simple quantitative method with "Bionic Glycome" as internal standard based on the high-throughput Matrix-assisted Laser Desorption/Ionization Mass Spectrometry (MALDI-MS). The quantitative results showed that there is a positive correlation between multi-antennary, sialylated N-glycans and CRC progress, while bi-antennary core-fucosylated N-glycans are negatively correlated with CRC progress. Machine learning is a powerful classification tool, suitable for mining big data, especially the large amount of data generated by high-throughput technologies. Using the predictive model constructed by machine learning, we obtained the classification accuracy of 75% for classification of 189 samples including CRC, advanced adenomas and healthy controls, and the accuracy of 87% for detection of the disease group that required treatment, including CRC and advanced adenomas. To our delight, the model successfully applied to the prediction of 176 samples collected a few months later, and five samples were wrongly predicted in the disease group. Overall, this diagnostic model we constructed here has valuable potential in the clinical application of detecting advanced adenomas and colorectal cancer and could compensate for the limitations of the current screening methods for detection of CRC and advanced adenomas.

Quantitative analysis of γ-glutamylisoleucine, γ-glutamylthreonine, and γ-glutamylvaline in HeLa cells using UHPLC-MS/MS

γ-Glutamylpeptides have been identified as potential biomarkers for a number of diseases including cancer, diabetes, and liver disease. In this study, we developed and validated a novel quantitative analytical strategy for measuring γ-glutamylisoleucine, γ-glutamylthreonine, and γ-glutamylvaline, all of which have been previously reported as potential biomarkers for prostate cancer in HeLa cells using ultra-high-performance liquid chromatography-tandem mass spectrometry. A BEH C18 column was used as the stationary phase. Mobile phase A was 99:1 water:formic acid and mobile phase B was acetonitrile. Chemical isotope labeling using benzoyl chloride was used as the internal standardization strategy. Sample preparation consisted of the addition of water to a frozen cell pellet, sonication, derivatization, centrifugation, and subsequent addition of an internal standard solution. The method was validated for selectivity, accuracy, precision, linearity, and stability. The determined concentrations of γ-glutamylisoleucine, γ-glutamylthreonine, and γ-glutamylvaline in HeLa cells were 1.92 ± 0.06, 10.8 ± 0.4, and 1.96 ± 0.04 pmol/mg protein, respectively. In addition, the qualitative analysis of these analytes in human serum was achieved using a modified sample preparation strategy. To the best of our knowledge, this is the first report of the use of benzoyl chloride for chemical isotope labeling for metabolite quantitation in cells.

A facile synthesis of isotope labeled acylcarnitines

Acylcarnitines are a big family of small molecule metabolites with various acyl groups attached to the hydroxyl moiety of l-carnitine. They are good indicators of multiple metabolic disorders. For instance, the newborn screening panel uses flow injection tandem mass spectrometry to analyze more than 30 different acylcarnitines and amino acids extracted from dried blood spots. A facile approach has been developed for the synthesis of isotope labeled acylcarnitines whose mass shift over their unlabeled counterparts can be any number in the range of 3 to 12 Da. This strategy makes it more convenient to provide authentic internal standards for acylcarnitines profiling analyses, thereby expanding their clinical applications.

Quantification of Teicoplanin Using the HPLC-UV Method for Clinical Applications in Critically Ill Patients in Korea

A high-performance liquid chromatography-ultraviolet detector (HPLC-UV) method has been used to quantify teicoplanin concentrations in human plasma. However, the limited analytical accuracy of previously bioanalytical methods for teicoplanin has given rise to uncertainty due to the use of an external standard. In this study, an internal standard (IS), polymyxin B, was applied to devise a precise, accurate, and feasible HPLC-UV method. The deproteinized plasma sample containing teicoplanin and an IS of acetonitrile was chromatographed on a C18 column with an acidic mobile phase consisting of NaH₂PO₄ buffer and acetonitrile (78:22, v/v) by isocratic elution and detection at 220 nm. The linearity was in the range 7.8–500 mg/L calculated by the ratio of the teicoplanin signal to the IS signal. This analytical method, validated by FDA guidelines with ICH Q2 (R1), was successfully applied to analyze the plasma samples of patients in the intensive care unit for treating serious resistant bacterial infectious diseases, such as those by methicillin-resistant Staphylococcus aureus and Enterococcus faecalis. The methods suggested the potential for use in routine clinical practice for therapeutic drug monitoring of teicoplanin, providing both improved accuracy and a wide range of linearity from lower than steady-state trough concentrations (10 mg/L) to much higher concentrations.

A Rapid and Feasible 1H-NMR Quantification Method of Ephedrine Alkaloids in Ephedra Herbal Preparations

A highly specific and sensitive proton nuclear magnetic resonance (¹H-NMR) method has been developed for the quantification of ephedrine alkaloid derivatives in Ephedra herbal commercial prescriptions. At the region of δ 4.0 to 5.0 ppm in the ¹H NMR spectrum, the characteristic signals are separated well from each other, and six analogues in total, methylephedrine (ME), ephedrine (EP), norephedrine (NE), norpseudoephedrine (NP), pseudoephedrine (PE), and methylpseudoephedrine (MP) could be identified. The quantities of these compounds are calculated by the relative ratio of the integral values of the target peak for each compound to the known concentrations of the internal standard anthracene. The present method allows for a rapid and simple quantification of ephedrine alkaloid derivatives in Ephedra-related commercial prescriptions without any preliminary purification steps and standard compounds, and accordingly it can be a powerful tool to verify different Ephedra species. In comparison to conventional chromatographic methods, the advantages of this method include the fact that no standard compounds are required, the quantification can be directly performed on the crude extracts, a better selectivity for various ephedrine alkaloid derivatives, and the fact that a very significant time-gain may be achieved.

An Update on MRMAssayDB: A Comprehensive Resource for Targeted Proteomics Assays in the Community

Precise multiplexed quantification of proteins in biological samples can be achieved by targeted proteomics using multiple or parallel reaction monitoring (MRM/PRM). Combined with internal standards, the method achieves very good repeatability and reproducibility enabling excellent protein quantification and allowing longitudinal and cohort studies. A laborious part of performing such experiments lies in the preparation steps dedicated to the development and validation of individual protein assays. Several public repositories host information on targeted proteomics assays, including NCI’s Clinical Proteomic Tumor Analysis Consortium assay portals, PeptideAtlas SRM Experiment Library, SRMAtlas, PanoramaWeb, and PeptideTracker, with all offering varying levels of details. We introduced MRMAssayDB in 2018 as an integrated resource for targeted proteomics assays. The Web-based application maps and links the assays from the repositories, includes comprehensive up-to-date protein and sequence annotations, and provides multiple visualization options on the peptide and protein level. We have extended MRMAssayDB with more assays and extensive annotations. Currently it contains >828 000 assays covering >51 000 proteins from 94 organisms, of which >17 000 proteins are present in >2400 biological pathways, and >48 000 mapping to >21 000 Gene Ontology terms. This is an increase of about four times the number of assays since introduction. We have expanded annotations of interaction, biological pathways, and disease associations. A newly added visualization module for coupled molecular structural annotation browsing allows the user to interactively examine peptide sequence and any known PTMs and disease mutations, and map all to available protein 3D structures. Because of its integrative approach, MRMAssayDB enables a holistic view of suitable proteotypic peptides and commonly used transitions in empirical data. Availability: http://mrmassaydb.proteincentre.com.

Addressing the standardisation of internal standards and preservative used in human bio fluids for NMR analysis: a method optimization

OBJECTIVES

A database comprising multivariate data in developing a model from nuclear magnetic resonance (NMR) analysis using human bio fluids are necessary to have reproducibility and reliability of the data. To achieve reproducibility of the data, standardised experiments, including internal standard and preservative used should be attained, especially for samples such as human bio fluids to hinder the variation among samples. The aim of the study was to optimise in commonly used human bio fluids (serum and urine) for a suitable internal standard and preservative used in extended storage samples for NMR analysis.

METHODS

Serum and urine samples were collected from healthy human subjects. The experiment was divided into two parts, part one to evaluate 2,2,2,2-tetradeutero-4,4-dimethyl-4-silapentanoic acid (TSP) and 4,4-dimethyl-4-silapentane-1-ammonium trifluoroacetate (DSA) as the optimal internal standard for the serum and urine samples. The second part investigated the effects of preservatives in the serum and urine samples on extended storage.

RESULTS

Overall, TSP and DSA are suitable to be used as an internal standard in human urine samples. However, DSA is a superior internal standard in serum samples for NMR analysis. For the effect of preservative, the results indicated that human serum and urine samples could be stored without addition of preservative in -80 °C, as no changes in NMR fingerprinting have been observed during storage in the absence or presence of the preservative.

CONCLUSIONS

The findings suggest the use of DSA and TSP as an internal standard in serum and urine samples, respectively. Storage of serum and urine samples without any addition of preservative for an extended period has no effect on the metabolites changes. By having a standardised method, it will offer a considerable saving in both operator and spectrometer time and most importantly produce reproducible and reliable data.

Addressing the standardisation of internal standards and preservative used in human bio fluids for NMR analysis: a method optimization

OBJECTIVES

A database comprising multivariate data in developing a model from nuclear magnetic resonance (NMR) analysis using human bio fluids are necessary to have reproducibility and reliability of the data. To achieve reproducibility of the data, standardised experiments, including internal standard and preservative used should be attained, especially for samples such as human bio fluids to hinder the variation among samples. The aim of the study was to optimise in commonly used human bio fluids (serum and urine) for a suitable internal standard and preservative used in extended storage samples for NMR analysis.

METHODS

Serum and urine samples were collected from healthy human subjects. The experiment was divided into two parts, part one to evaluate 2,2,2,2-tetradeutero-4,4-dimethyl-4-silapentanoic acid (TSP) and 4,4-dimethyl-4-silapentane-1-ammonium trifluoroacetate (DSA) as the optimal internal standard for the serum and urine samples. The second part investigated the effects of preservatives in the serum and urine samples on extended storage.

RESULTS

Overall, TSP and DSA are suitable to be used as an internal standard in human urine samples. However, DSA is a superior internal standard in serum samples for NMR analysis. For the effect of preservative, the results indicated that human serum and urine samples could be stored without addition of preservative in -80 °C, as no changes in NMR fingerprinting have been observed during storage in the absence or presence of the preservative.

CONCLUSIONS

The findings suggest the use of DSA and TSP as an internal standard in serum and urine samples, respectively. Storage of serum and urine samples without any addition of preservative for an extended period has no effect on the metabolites changes. By having a standardised method, it will offer a considerable saving in both operator and spectrometer time and most importantly produce reproducible and reliable data.

Enhanced Metabolome Coverage and Evaluation of Matrix Effects by the Use of Experimental-Condition-Matched 13C-Labeled Biological Samples in Isotope-Assisted LC-HRMS Metabolomics

Stable isotope-assisted approaches can improve untargeted liquid chromatography-high resolution mass spectrometry (LC-HRMS) metabolomics studies. Here, we demonstrate at the example of chemically stressed wheat that metabolome-wide internal standardization by globally ¹³C-labeled metabolite extract (GLMe-IS) of experimental-condition-matched biological samples can help to improve the detection of treatment-relevant metabolites and can aid in the post-acquisition assessment of putative matrix effects in samples obtained upon different treatments. For this, native extracts of toxin- and mock-treated (control) wheat ears were standardized by the addition of uniformly ¹³C-labeled wheat ear extracts that were cultivated under similar experimental conditions (toxin-treatment and control) and measured with LC-HRMS. The results show that 996 wheat-derived metabolites were detected with the non-condition-matched ¹³C-labeled metabolite extract, while another 68 were only covered by the experimental-condition-matched GLMe-IS. Additional testing is performed with the assumption that GLMe-IS enables compensation for matrix effects. Although on average no severe matrix differences between both experimental conditions were found, individual metabolites may be affected as is demonstrated by wrong decisions with respect to the classification of significantly altered metabolites. When GLMe-IS was applied to compensate for matrix effects, 272 metabolites showed significantly altered levels between treated and control samples, 42 of which would not have been classified as such without GLMe-IS.

Genome Size of 17 Species From Caelifera (Orthoptera) and Determination of Internal Standards With Very Large Genome Size in Insecta

Comparative studies of insect genome size show that Orthoptera is a unique group of Insecta with a significantly enlarged genome. To determine a suitable internal standard for a large genome and to compare the effects of different internal standards on estimates of genome size, we used four internal standards to estimate nuclear DNA content in nine insect species with large genomes. The results showed that the combination of two internal standards, Locusta migratoria (♂1C = 6.20 pg, ♀1C = 6.60 pg) and Periplaneta americana♂ (1C = 3.41 pg), was suitable for estimating large genome of Caelifera by flow cytometry. Using these two internal standards, we estimated the genome sizes of 17 species of Caelifera (12 genera in Acrididae, 2 genera in Pamphagidae, 1 genus in Pyrgomorphidae) using flow cytometry. Genomes ranged from 6.57 pg (Shirakiacris shirakii) to 18.64 pg (Bryodemella holdereri), the largest described in insects to date. These species showed significant genomic dimorphism based on sex: females had a 0.56 pg larger genome than males on average, which might be due to the sex chromosome determinism mechanism of X0(♂)/XX(♀). To test the results obtained by flow cytometry, we used k-mers of Illumina sequencing data to gauge the C-value of Calliptamus abbreviatus and Haplotropis brunneriana. The results of the two methods are slightly different. Genomes were estimated to be about 0.28 and 0.26 pg smaller, respectively, than the flow cytometry values. Furthermore, we also reconstructed the evolutionary relationships of these taxa and discuss the genome size evolution in a phylogenetic framework.

The quest for absolute abundance: The use of internal standards for DNA-based community ecology

To characterize microbiomes and other ecological assemblages, ecologists routinely sequence and compare loci that differ among focal taxa. Counts of these sequences convey information regarding the occurrence and relative abundances of taxa, but provide no direct measure of their absolute abundances, due to the technical limitations of the sequencing process. The relative abundances in compositional data are inherently constrained and difficult to interpret. The incorporation of internal standards (ISDs; colloquially referred to as 'spike-ins') into DNA pools can ameliorate the problems posed by relative abundance data and allow absolute abundances to be approximated. Unfortunately, many laboratory and sampling biases cause ISDs to underperform or fail. Here, we discuss how careful deployment of ISDs can avoid these complications and be an integral component of well-designed studies seeking to characterize ecological assemblages via sequencing of DNA.

Enantioselective synthesis of tri-deuterated (-)-geosmin to be used as internal standard in quantitation assays

For the accurate and sensitive quantitation of the off-flavor compound geosmin, particularly in complex matrices, a stable isotopologue as internal standard is highly advantageous. In this work, we present a versatile synthetic strategy leading from (4aR)-1,4a-dimethyl-4,4a,5,6,7,8-hexahydronaphthalen-2(3H)-one to tri-deuterated (-)-geosmin ((4S,4aS,8aR)-4,8a-dimethyl(3,3,4-² H₃ )octahydronaphthalen-4a(2H)-ol). The starting material was readily accessible from inexpensive 2-methylcyclohexan-1-one using previously published procedures.

Development of a Real-Time TaqMan PCR Method for Absolute Quantification of the Biocontrol Agent Esteya vermicola

Esteya vermicola has been used as an effective biocontrol agent for the management of the pinewood nematode, Bursaphelenchus xylophilus. Tools for monitoring the colonization and parasitism patterns of E. vermicola are required for the development of highly effective biocontrol strategies. Because the TaqMan PCR technique is effective for quantification of species in environmental samples, a real-time PCR-based methodology was developed for absolute quantification of E. vermicola via internal standard addition and extrapolation of DNA quantity to hyphal length. Primers and a probe for the 28S ribosomal RNA gene of E. vermicola were designed, and nested TaqMan real-time PCR-based quantification was performed. In addition, internal standard-based yield measurement was correlated to the absolute quantity of target genomic DNA. Moreover, an extrapolation curve obtained by optical microscopy and image analysis of the mycelia was constructed for the measurement of fungal hyphal length. The absolute quantification method developed in the present study provides a sensitive and accurate technique to quantify fungal density in either wood or other substrate samples and can be used as an effective tool for future studies of biocontrol agents.

Evaluation, identification and impact assessment of abnormal internal standard response variability in regulated LC-MS bioanalysis

Internal standard (IS) plays an important role in LC-MS bioanalysis by compensating for the variability of the analyte of interest in bioanalytical workflow. Due to the complexity of biological sample compositions and bioanalytical processes, a certain level of IS response variability across a run or a study is anticipated. However, an extensive variability may raise doubts to the accuracy of the measured results and also suggest nonoptimal analytical method. In this current paper, recent publications and guidelines regarding IS response in LC-MS bioanalysis were thoroughly reviewed with focus on the evaluation, identification and impact assessment of 'abnormal' IS response variability. A systematic decision tree was proposed to facilitate investigation into abnormal IS response variability after each run.

The perspectives of ethanol usage as an internal standard for the quantification of volatile compounds in alcoholic products by GC-MS

The potential use of ethanol as an internal standard (IS) for GC-MS analysis was studied. The paper describes the analysis of spirit drinks and other alcoholic products which consist of a mixture of water, ethanol, and volatile compounds. In the suggested method, ethanol was employed as an IS for the common procedure of volatile compounds quantification. A number of standard solutions of nine compounds with different concentrations was prepared in a water-ethanol matrix and measured with GC-MS in the SIM mode. Two possible approaches were suggested to avoid detector saturation during ethanol detection. The first one consisted in using less abundant m/z 47 as quantifiers. These ions mainly correspond to unfragmented heavy ethanol molecules containing one ¹³ C isotope. The second method consisted in reduction of the voltage of MS electron multiplier. The experiment also included the preparation and subsequent dilution of the standard solution and ethanol with water, which determined the linearity of the modified MS response relative to the ethanol content. Analysis of the obtained results revealed that volatile compounds can be successfully accurately determined with GC-MS by employing ethanol as an IS. Application of the suggested method is not limited to the reported volatile compounds and alcoholic products.

Simultaneous analysis of seven neonicotinoid pesticides in agricultural products involving solid-phase extraction and surrogate compensation using liquid chromatography-tandem mass spectrometry

This study proposes a practical and precise method for the simultaneous analysis of seven neonicotinoid pesticides in agricultural products using liquid chromatography-tandem mass spectrometry from two different approaches. First, the applicability of a cleanup cartridge, comprised of a polymer sorbent consisting of a styrene-divinylbenzene copolymer with N-containing polar groups and methacrylate, in food samples was demonstrated for the first time. Second, applying an internal standard (IS) calibration method at a lower cost was considered by changing the timing of the IS addition and selecting the minimum number of ISs by referring on the matrix effect. The proposed method resulted in excellent recoveries in all tested matrices (brown rice, grapes, and peanuts) at a spiked concentration of 0.01 mg/kg. Subsequently, a residue analysis of hagobou (young burdock) was conducted. Imidacloprid was detected at 0.02 mg/kg, and the recoveries calculated in parallel with the analysis were satisfactory.

Gold Nanorod Array-Bridged Internal-Standard SERS Tags: From Ultrasensitivity to Multifunctionality

Bimetallic gold core-silver shell (Au@Ag) surface-enhanced Raman scattering (SERS) tags draw broad interest in the fields of biological and environmental analysis. In reported tags, silver coating tended to smooth the surface and merge the original hotspot of Au cores, which was disadvantageous to signal enhancement from the aspect of surface topography. Herein, we developed gold nanorod (AuNR)-bridged Au@Ag SERS tags with uniform three-dimensional (3D) topography for the first time. This unique structure was achieved by selecting waxberry-like Au nanoparticles (NPs) as cores, which were capped by vertically oriented AuNR arrays. Upon selective surface blocking with thiol-ligands, Ag NPs were controlled to anisotropically grow on the tips of the AuNRs, producing high-density homo- (Ag-Ag) and hetero- (Au-Ag) hotspots in a single NP. The 3D hotspots rendered this NP extraordinary SERS enhancement ability (an analytical enhancement factor of 3.4 × 10⁶) 30 times higher than the counterpart with a smooth surface, realizing signal detection from a single NP. More importantly, multiplexing signals ("blank" or multiplex "internal standard") can be achieved by simply changing thiol-ligands, as exemplified in the synthesis of NPs with 8 signatures. Furthermore, the multifunctionality has been demonstrated in living cell/in vivo imaging, photothermal therapy, and SERS substrates for ratiometric quantitative analysis, relying on the inherent internal standard signal. The prepared Au@Ag NPs have great potential as standard tools in many SERS-related fields.

Systematic internal standard variability and issue resolution: two case studies

Two case studies are presented of validated assays where the internal standard showed high variability, and there was a clear response difference between study samples and standards and quality controls. In the first case a co-eluting peak boosted the stable isotope labeled internal standard response in samples from hepatically impaired subjects. In the second case the blank plasma matrix suppressed the structural analog internal standard response. For both assays the issue could be resolved by adapting the chromatographic conditions and re-validating the assay (case 1) or by diluting the study samples with blank plasma (case 2).

4-Mercaptobenzoic Acid Labeled Gold-Silver-Alloy-Embedded Silica Nanoparticles as an Internal Standard Containing Nanostructures for Sensitive Quantitative Thiram Detection

In this study, SiO2@Au@4-MBA@Ag (4-mercaptobenzoic acid labeled gold-silver-alloy-embedded silica nanoparticles) nanomaterials were investigated for the detection of thiram, a pesticide. First, the presence of Au@4-MBA@Ag alloys on the surface of SiO2 was confirmed by the broad bands of ultraviolet-visible spectra in the range of 320-800 nm. The effect of the 4-MBA (4-mercaptobenzoic acid) concentration on the Ag shell deposition and its intrinsic SERS (surface-enhanced Raman scattering) signal was also studied. Ag shells were well coated on SiO2@Au@4-MBA in the range of 1-1000 µM. The SERS intensity of thiram-incubated SiO2@Au@4-MBA@Ag achieved the highest value by incubation with 500 µL thiram for 30 min, and SERS was measured at 200 µg/mL SiO2@Au@4-MBA@Ag. Finally, the SERS intensity of thiram at 560 cm-1 increased proportionally with the increase in thiram concentration in the range of 240-2400 ppb, with a limit of detection (LOD) of 72 ppb.

Towards Quantitative Microbiome Community Profiling Using Internal Standards

An inherent issue in high-throughput rRNA gene tag sequencing microbiome surveys is that they provide compositional data in relative abundances. This often leads to spurious correlations, making the interpretation of relationships to biogeochemical rates challenging. To overcome this issue, we quantitatively estimated the abundance of microorganisms by spiking in known amounts of internal DNA standards. Using a 3-year sample set of diverse microbial communities from the Western Antarctica Peninsula, we demonstrated that the internal standard method yielded community profiles and taxon cooccurrence patterns substantially different from those derived using relative abundances. We found that the method provided results consistent with the traditional CHEMTAX analysis of pigments and total bacterial counts by flow cytometry. Using the internal standard method, we also showed that chloroplast 16S rRNA gene data in microbial surveys can be used to estimate abundances of certain eukaryotic phototrophs such as cryptophytes and diatoms. In Phaeocystis, scatter in the 16S/18S rRNA gene ratio may be explained by physiological adaptation to environmental conditions. We conclude that the internal standard method, when applied to rRNA gene microbial community profiling, is quantitative and that its application will substantially improve our understanding of microbial ecosystems.IMPORTANCE High-throughput-sequencing-based marine microbiome profiling is rapidly expanding and changing how we study the oceans. Although powerful, the technique is not fully quantitative; it provides taxon counts only in relative abundances. In order to address this issue, we present a method to quantitatively estimate microbial abundances per unit volume of seawater filtered by spiking known amounts of internal DNA standards into each sample. We validated this method by comparing the calculated abundances to other independent estimates, including chemical markers (pigments) and total bacterial cell counts by flow cytometry. The internal standard approach allows us to quantitatively estimate and compare marine microbial community profiles, with important implications for linking environmental microbiomes to quantitative processes such as metabolic and biogeochemical rates.

Nuclear Genome Size in Contrast to Sex Chromosome Number Variability in the Human Bed Bug, Cimex lectularius (Heteroptera: Cimicidae)

The human bed bug Cimex lectularius is one of the most prevalent human ectoparasites in temperate climate zones. The cytogenetic features of this resilient pest include holokinetic chromosomes, special chromosome behavior in meiosis, and numerical variation of chromosomes, where the diploid number ranges from 26 + X₁ X₂ Y to 26 + X_1-20 Y. It is desirable to assess the nuclear DNA content of various cytotypes for a further detailed study of the C. lectularius genome. Detailed knowledge of the DNA content of this parasite could also clarify the origin of additional chromosomes. The average nuclear genome size C. lectularius with 2n = 26 + X₁ X₂ Y is 2C = 1.94 pg for males and 1.95 pg for females. There is a significant correlation between genome size and the number of chromosomes, but in some specimens with additional chromosomes, nuclear genome size decreases or remains average. Several species used as the internal reference standard were tested for further investigations of genome size in C. lectularius, and the plant Solanum pseudocaspicum turned out to be the most suitable. © 2019 International Society for Advancement of Cytometry.

Quantitative analysis of genetically modified soya using multiple reaction monitoring mass spectrometry with endogenous peptides as internal standards

A simple label-free method was developed for the quantification of the herbicide-resistant gene-related protein 5-enolpyruvylshikimate-3-phosphate synthase using multiple reaction monitoring liquid chromatography-mass spectrometry. Sample pretreatment procedures including ion exchange chromatography and CaCl2 precipitation were used to purify the 5-enolpyruvylshikimate-3-phosphate synthase protein. Quantification of various percentages of genetically modified soya (0.5-100%) was performed by selecting suitable endogenous soybean peptides as internal standards. Results indicated that Gly P (QGDVFVVPR) and Lec P (LQLNK) are useful internal standards for the quantification of low and high percentages of genetically modified soya, respectively. Linear regression analysis of both calibration curves yielded good linearity with R2 of 0.99. This approach is a convenient and accurate quantification method for genetically modified soya at a level as low as 0.5% (less than the current EU threshold for labeling genetically modified soya).

Synthesis of [15 N4 ] purine labeled cytokinin glycosides derived from zeatins and topolins with 9-β-d, 7-β-d-glucopyranosyl, or 9-β-d-ribofuranosyl group

Synthesis of [¹⁵ N₄ ] purine labeled cytokinine glycosides derived from zeatins and topolins containing a 9-β-d, 7-β-d-glucopyranosyl, or 9-β-d-ribofuranosyl group is described. These N⁶ -substituted adenine derivatives are intended as internal analytic standards for phytohormone analysis. All labeled compounds were prepared from 6-chloro[¹⁵ N₄ ]purine (1). The equilibrium reaction of 1 with acetobromo-α-d-glucose gave isomeric 7-β-d (3) and 9-β-d (4) chloro glucosyl precursors, which were treated with the corresponding amines to get desired labeled cytokinin 7-β-d (6) and 9-β-d (5) glucopyranosides. Cytokinins containing 9-β-d-ribofuranosyl group (8) were obtained by direct enzymatic transglycosylation reaction of cytokinins (7) prepared from 6-chloro[¹⁵ N₄ ] purine (1).

Multilayer Ag-Embedded Silica Nanostructure as a Surface-Enhanced Raman Scattering-Based Chemical Sensor with Dual-Function Internal Standards

Surface-enhanced Raman scattering (SERS) spectroscopy is attractive in various detection analysis fields. However, the quantitative method using SERS spectroscopy remains as an area to be developed. The key issues in developing quantitative analysis methods by using SERS spectroscopy are the fabrication of reliable SERS-active materials such as nanoparticle-based structures and the acquisition of the SERS signal without any disturbance that may change the SERS signal intensity and frequency. Here, the fabrication of seamless multilayered core-shell nanoparticles with an embedded Raman label compound as an internal standard (ML_RLC dots) for quantitative SERS analysis is reported. The embedded Raman label compound in the nanostructure provides a reference value for calibrating the SERS signals. By using the ML_RLC dots, it is possible to gain target analyte signals of different concentrations while retaining the Raman signal of the internal standard. The ML_4-BBT dots, containing 4-bromobenzenethiol (4-BBT) as an internal standard, are successfully applied in the quantitative analysis of 4-fluorobenzenethiol and thiram, a model pesticide. Additionally, ratiometric analysis was proved practical through normalization of the relative SERS intensity. The ratiometric strategy could be applied to various SERS substrates for quantitative detection of a wide variety of targets.

Identification of unexpected unlabeled N,N-dimethylamide formation in the synthesis of deuterated fragment of ribociclib by a HATU-mediated coupling reaction

Starting from N,N-dimethylamine and D₂ O, deuterated fragment of ribociclib was synthesized for use as a mass spectroscopy internal standard. Furthermore, systematic studies on D₀ (unlabeled material) formation during the amidation reaction were performed, leading to the identification of a coupling reagent, HATU (O-(7-azabenzotriazol-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate), as main cause. Finally, an alternative route was designed using EDCI/HOBT as coupling reagents to produce the desired deuterated compound without D₀ residue.

Applications and Uncertainty Estimation of Single Level Standard Addition Method ICP-MS for Elemental Analysis in Various Matrix

The standard addition method (SAM) based on gravimetric sample preparation was investigated as an approach for the removal or cancelling of matrix effects in measurements by inductively coupled plasma mass spectrometry (ICP-MS). Deduction of the equations and experimental confirmation of the method are both given in the present work. After measuring both spiked and non-spiked samples by ICP-MS, the concentration of an element could be calculated based on the signal intensity ratio to an internal standard. A practical example was provided for the measurement of Fe in a certified reference material (CRM), i.e. NMIJ CRM 7512-a (milk powder). The validity of the method had been confirmed by the results of international comparisons with various kinds of matrix, including bioethanol, human serum, biodiesel fuel, drinking water, infant formula milk power, and seafood. The suggested method had been applied to measurements of multiple elements in three CRMs, including tap water, milk powder, and tea leave powder, respectively.