MATRIX EFFECTS IN LIQUID CHROMATOGRAPHY-MASS SPECTROMETRY

Quaternary ammonium compounds in medicinal herbs and health risk assessment

The rising global demand for medicinal herbs has increased human consumption, raising concerns about potential health risks related to quaternary ammonium compounds (QACs), especially among infants due to frequent use in certain cultures. To perform a market survey, an LC-ESI-MS/MS method was developed to detect five QACs, including Benzalkonium Chlorides (BACs) and Dialkyl Dimethyl Ammonium Chloride (DDAC), in dry medicinal herbs. The method employed QuEChERS extraction with acetonitrile and achieved chromatographic separation with a poroshell C18 column. Method validation was conducted according to Eurachem and SANTE/11312/2021 guidelines, showing high sensitivity and selectivity, with recoveries between 70% and 110% and RSDs below 5%. The method was applied to market samples, resulting in 33% exceedances of the maximum residue limits. In this study also dietary exposure risks for adults, toddlers and infants were evaluated. Preliminary risk assessment indicated acceptable dietary exposure risks.

Direct analysis of biotransformations with mass spectrometry-DiBT-MS

The development and analysis of engineered enzymes is greatly assisted by the use of high-throughput screening to quickly determine the efficacy of biotransformations under various conditions. Ambient ionization, particularly desorption electrospray ionization (DESI), coupled to high-resolution mass spectrometry has the advantages of minimal requirements for sample preparation before analysis, which renders it suitable for high-throughput screening, in which the accurate mass and potentially the tandem mass spectrometry (MS) fingerprint for any given product can be used for identification. We present a protocol that permits the application of this method in routine biotechnology and chemical biology laboratories that are using engineered enzymes (such as imine reductases and carboxylic acid reductases, mentioned herein) to produce target compounds from substrates (quinoline moieties and phenyl(piperazinyl) moieties, respectively). Through the use of DESI's MS imaging capabilities, reaction monitoring can be easily visualized via imaging of selected substrate or product ions in a convenient, user-friendly workflow. We describe here how DESI-MS can be used to directly analyze the activity of biotransformations from crude cell lysate, which we term 'DiBT-MS'. The DiBT-MS method presented here is 10-1,000 times as fast as liquid chromatography-MS, with the full procedure for 96 samples taking ~2 h and consuming far less solvent and sample. Also demonstrated in this protocol is the impact of solvent spray composition on ionization efficiency of the target analyte, the benefits of a nylon membrane slide and the reusability of sample slides in multiple experiments.

Matrix effects in ultra-high performance supercritical fluid chromatography-mass spectrometry analysis of vitamin E in plasma: The effect of sample preparation and data processing

The approaches to matrix effects determination and reduction in ultra-high performance supercritical fluid chromatography with mass spectrometry detection have been evaluated in this study using different sample preparation methods and investigation of different calibration models. Five sample preparation methods, including protein precipitation, liquid-liquid extraction, supported liquid extraction, and solid phase extraction based on both "bind and elute" and "interferent removal" modes, were optimized with an emphasis on the matrix effects and recovery of 8 forms of vitamin E, including α-, β-, γ-, and δ-tocopherols and tocotrienols, from plasma. The matrix effect evaluation included the use and comparison of external and internal calibration using three models, i.e., least square with no transformation and no weighting (1/x0), with 1/x2 weighting, and with logarithmic transformation. The calibration model with logarithmic transformation provided the lowest %-errors and the best fits. Moreover, the type of the calibration model significantly affected not only the fit of the data but also the matrix effects when evaluating them based on the comparison of calibration curve slopes. Indeed, based on the used calibration model, the matrix effects calculated from calibration slopes ranged from +92% to - 72% for α-tocopherol and from -77% to +19% in the case of δ-tocotrienol. Thus, it was crucial to calculate the matrix effect by Matuszewski's post-extraction approach at six concentration levels. Indeed, a strong concentration dependence was observed for all optimized sample preparation methods, even if the stable isotopically labelled internal standards (SIL-IS) were used for compensation. The significant differences between individual concentration levels and compounds were observed, even when the tested calibration range covered only one order of magnitude. In methods with wider calibration ranges, the inappropriate use of calibration slope comparison instead of the post-extraction addition approach could result in false negative results of matrix effects. In the selected example of vitamin E, solid-phase extraction was the least affected by matrix effects when used in interferent removal mode, but supported liquid extraction resulted in the highest recoveries. We showed that the calibration model, the use of a SIL-IS, and the analyte concentration level played a crucial role in the matrix effects. Moreover, the matrix effects can significantly differ for compounds with similar physicochemical properties and close retention times. Thus, in all bioanalytical applications, where different analytes are typically determined in one analytical run, it is necessary to carefully select the data processing in addition to the method for the sample preparation, SIL-IS, and chromatography.

Nitrogen-doped magnetic porous carbon nanospheres derived from dual templates-induced mesoporous polydopamine coated Fe3O4 for efficient extraction and sensitive determination of volatile nitrosamines by gas chromatography-mass spectroscopy

N-nitrosamines (NAs) are highly carcinogenic compounds commonly found in food, beverages, and consumer products. Due to their wide polarity range, it is challenging to find a suitable carbon adsorbent that can simultaneously adsorb and enrich both polar and nonpolar NAs with good recovery. In this study, nitrogen-doped magnetic mesoporous carbon nanospheres (M-MCN) were prepared and employed as an adsorbent for magnetic solid-phase extraction (MSPE) to extract and concentrate four NAs. The introduction of nitrogen functional groups enhanced the hydrophilicity of the carbon material, allowing M-MCN to achieve a balance between hydrophilicity and hydrophobicity, resulting in good recovery for both polar and nonpolar NAs. A method combining MSPE with gas chromatography-mass spectrometry (GC-MS) was developed for the determination of NAs in processed meat and alcoholic beverages. The method exhibited a good linear range (1-100 ng g-1, r2 > 0.9967) and trace-level detection (0.53-6.6 ng g-1). The recovery rates for the four NAs ranged between 85.7 and 110.7 %, with intra-day precision expressed as relative standard deviation (RSD) between 4.1 and 10.7 %, and inter-day precision between 4.8 and 12.9 %. The results demonstrated not only good accuracy and precision but also provided a new adsorbent for the enrichment of trace-level NAs in processed meat and alcoholic beverage samples.

Applications of chromatographic methods in metabolomics: A review

Chromatography is a robust and reliable separation method that can use various stationary phases to separate complex mixtures commonly seen in metabolomics. This review examines the types of chromatography and stationary phases that have been used in targeted or untargeted metabolomics with methods such as mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectroscopy. General considerations for sample pretreatment and separations in metabolomics are considered, along with the various supports and separation formats for chromatography that have been used in such work. The types of liquid chromatography (LC) that have been most extensively used in metabolomics will be examined, such as reversed-phase liquid chromatography and hydrophilic liquid interaction chromatography. In addition, other forms of LC that have been used in more limited applications for metabolomics (e.g., ion-exchange, size-exclusion, and affinity methods) will be discussed to illustrate how these techniques may be utilized for new and future research in this field. Multidimensional LC methods are also discussed, as well as the use of gas chromatography and supercritical fluid chromatography in metabolomics. In addition, the roles of chromatography in NMR- vs. MS-based metabolomics are considered. Applications are given within the field of metabolomics for each type of chromatography, along with potential advantages or limitations of these separation methods.

An accurate and precise liquid chromatography-tandem mass spectrometry method for the determination of six phosphatidylethanol homologues in whole blood with phospholipid interferences minimized

Alcohol consumption is associated with a wide risk of different diseases, injury and death, and has significant social and economic consequences worldwide. Phosphatidylethanol (PEth) is a group of promising direct alcohol biomarkers, with a significantly longer half-life in blood than ethanol, which can be measured to predict different drinking patterns, such as heavy- and social drinking. This study aimed to develop and validate an accurate and precise LC-MS/MS method for the determination of six PEth homologues in whole blood with minimal interference from unwanted phospholipids. Different organic solvent mixtures for liquid-liquid extraction were investigated to obtain satisfactory recovery of PEth homologues and removal of the lyso-phospholipids and other early eluting phospholipids. The mixture of heptane/2-propanol (80:20, v:v) gave lower phospholipid background and better signal/noise values for the PEth peaks. An LC-MS/MS TQ-S system from Waters was used for the instrumental analysis. The main part of unwanted phospholipids were separated from the PEth homologues on an Acquity BEH C18 column (50 × 2.1 mm ID, 1.7 µm particles) using a buffer-free mobile phase of 0.025 % ammonia in Type 1 water, pH 10.7, as solvent A and methanol as solvent B. Validation and quantification of 22 authentic blood samples showed that the developed LC-MS/MS method is sensitive, precise and accurate for the determination of the six PEth homologues in whole blood. Lower limit of quantification was 10 nM for all compounds. No matrix effects were observed, possibly due to the successful strategies incorporated to avoid the influence of unwanted phospholipids.

Interaction between Six Waxy Components in Summer Black Grapes (Vitis vinifera) and Mancozeb and Its Effect on the Residue of Mancozeb

Mancozeb, an antifungal typically used for the growth of fruits, has the characteristic of non-internal absorption, and has a risk of binding to the waxy components of fruits. This work investigated the interaction of pesticide molecules with the waxy layer on the grape surface and their effects on pesticide residues in grapes. The study observed significant changes in the compositions of the waxy layer on the grape surface after soaking in a mancozeb standard solution. The six substances-oleanolic acid, ursolic acid, lupeol, octacosanol, hexacosanal, and γ-sitosterol-with discernible content differences were chosen for molecular docking. Docking results were further visualized by an independent gradient model based on Hirshfeld partition (IGMH). Hydrogen bonds and van der Waals forces were found between mancozeb and the six waxy components. Moreover, the negative matrix effects caused by the presence or absence of wax for the determination of mancozeb were different through the QuEChERS-HPLC-MS method. Compared with the residue of mancozeb in grapes (5.97 mg/kg), the deposition of mancozeb in grapes after dewaxing was significantly lower (1.12 mg/kg), which further supports that mancozeb may interact with the wax layer compositions. This work not only provides insights into the study of the interaction between pesticides and small molecules but also provides theoretical guidelines for the investigation of the removal of pesticide residues on the surface of fruits.

Validation of analytical method of cannabinoids: Novel approach using turbo-extraction

The development of simple, efficient, and low-cost analytical methods is essential for the evaluation and monitoring of the main cannabinoids in Cannabis-based products. In this sense, the objectives of this study were to develop and validate an analytical method for obtaining and determining cannabinoids in a pool sample. Two extraction techniques were used, ultrasound and turbo-extraction, and two system-solvents, methanol:chloroform (9:1 v:v) and ethanol. The analytical method used and validated was carried out in High Performance Liquid Chromatography with Diodes Array Detector. The cannabidiol standard was characterized by a nuclear magnetic resonance. The use of the proposed method makes it possible to identify cannabinoids, both in the acid form and in the neutral form, in 7 min of analysis. The results confirmed high precision and accuracy. The detection and quantification limits were 0.19 μg/mL and 5 μg/mL, respectively. The method developed proved to be selective and robust for the evaluation of cannabinoids. It is hoped that the methods developed can be used to obtain and analyze cannabinoids, both for medicinal purposes and for forensic analysis.

Enhanced microfluidic open interface for the direct coupling of solid phase microextraction with liquid electron ionization-tandem mass spectrometry

Solid-phase microextraction (SPME) directly coupled to MS is a widespread technique for determining small molecules in different matrices in many application fields. Here we present a modified microfluidic open interface (MOI) connected to a passive-flow-splitter device (PFS) for the direct coupling of SPME to a liquid-electron ionization (LEI) interface in a tandem mass spectrometer for the analysis of complex biological samples. No chromatographic separation is involved. The new MOI-PFS configuration was designed to speed up the sample transfer to MS, improving the signal-to-noise ratio and peak shape and leading to fast and sensitive results. MOI-PFS-LEI-MS/MS experiments were conducted using fentanyl as a model compound in water and blood serum. The method uses a C18 Bio-SPME fiber by direct immersion (3 min) in 300 µL of the sample followed by rapid desorption (1 min) in a flow isolated volume (MOI chamber, 2.5 µL) filled with 100% acetonitrile. The PFS permits the rapid transfer of a fraction of the sample into the MS via the LEI interface. The optimal conditions were obtained at a flow rate of 10 µL·min^-1 and a 1:20 split ratio. Altogether, extraction, desorption, and analysis require approximately 5 min. Good interday and intraday precision, excellent linearity and LOQs in the µg·L^-1 range were obtained for fentanyl in water and serum. Greenness evaluation demonstrated a limited environmental impact of this technique.

The history of electron ionization in LC-MS, from the early days to modern technologies: A review

This review article traces the history of the use of liquid chromatography coupled with mass spectrometry (LC-MS) using electron ionization (EI) from the first attempts up to the present day. At the time of the first efforts to couple LC to MS, 70 eV EI was the most common ionization technique, typically used in gas chromatography-mass spectrometry (GC-MS) and providing highly reproducible mass spectra that could be collated in libraries. Therefore, it was obvious to transport this dominant approach to the early LC-MS coupling attempts. The use of LC coupled to EI-MS is challenging mainly due to restrictions related to high-vacuum and high-temperature conditions required for the operation of EI and the need to remove the eluent carrying the analyte before entering the ion source. The authors will take readers through a journey of about 50 years, showing how through the succession of different attempts it has been possible to successfully couple LC with EI-MS, which in principle appear to be incompatible.

A quantitative method for the selective 5-HT2A agonist 25CN-NBOH in rat plasma and brain

In recent years, agonists of the 5-HT_2A receptor have gained increasing attention for their potential therapeutic use to treat psychological disorders such as anxiety and depression. Here, we report the development and validation of an LC-MSMS based analytical method for the quantification of the novel selective 5-HT_2A agonist 25CN-NBOH in rat plasma and brain. As simple and efficient sample clean-up we applied the Phree Phospholipid Removal approach from Phenomenex, which is particularly novel for brain samples. In order to investigate the metabolic stability of 25CN-NBOH in vitro biotransformation studies with recombinant enzymes and human liver microsomes were conducted. Several biotransformation products and pathways could be identified. Based on the in vitro study one of the putative metabolites (2C-CN) was included in the analytical method development. To test the methods applicability 25CN-NBOH was quantified in plasma and brain samples from a pharmacokinetic in vivo study with Wildtype Long Evans rats. Both the in vitro metabolism data as well as the in vivo PK data suggest that 25CN-NBOH is susceptible to metabolism, but is degraded slower and is more stable compared to other NBOMe's investigated to date. The developed analytical method might serve as basis to include further 25CN-NBOH metabolites. It is expected to facilitate further preclinical and clinical investigations of 25CN-NBOH in biological matrices.

Direct Coupling of Bio-SPME to Liquid Electron Ionization-MS/MS via a Modified Microfluidic Open Interface

We present a modified microfluidic open interface (MOI) for the direct coupling of Bio-SPME to a liquid electron ionization-tandem mass spectrometry (LEI-MS/MS) system as a sensitive technique that can directly analyze biological samples without the need for sample cleanup or chromatographic separations as well as without measurable matrix effects (ME). We selected fentanyl as test compound. The method uses a C18 Bio-SPME fiber by direct immersion (DI) in urine and plasma and the subsequent quick desorption (1 min) in a flow-isolated volume (2.5 μL) filled with an internal standard-acetonitrile solution. The sample is then transferred to an EI source of a triple-quadrupole mass spectrometer via a LEI interface at a nanoscale flow rate. The desorption and analysis procedure requires less than 10 min. Up to 150 samples can be analyzed without observing a performance decline, with fentanyl quantitation at microgram-per-liter levels. The method workflow is extremely dependable, relatively fast, sustainable, and leads to reproducible results that enable the high-throughput screening of various biological samples.

Cloud Point Extraction in the Determination of Drugs in Biological Matrices

Cloud point extraction (CPE) is a simple, safe and environment-friendly technique used in the preparation of various samples. It was primarily developed for the assessment of environmental samples, especially analyzed for metals. Recently, this technique has been used in the extraction and determination of various chemical compounds (e.g., drugs, pesticides and vitamins), in various matrices (e.g., human plasma, human serum, milk and urine). In this review, we show that CPE is a reliable method of extraction and can be used in analytical laboratories in combination with other techniques that can be used in the determination of drugs and other chemicals in the human biological matrix. According to the literature, a combination of different methods provides good recovery and can be used in the simultaneous determination of many drugs in a single analysis. CPE can be optimized by changing its conditions (e.g., type of surfactant used, incubation temperature, pH and the addition of salts). In this review, we present the optimized CPE methods used in the determination of various pharmaceuticals and describe how the conditions affect the performance of extraction. This data might support future designing of the new CPE applications that are simple and more accurate. We compared CPE with other extraction methods and also showed the advantages and disadvantages of various extraction techniques along with a discussion on their environmental impact. According to the publications reviewed, it is obvious that CPE is an easy, safe, rapid and inexpensive method of extraction.

Analysis of pharmaceuticals in fish using ultrasound extraction and dispersive spe clean-up on que Z-Sep/C18 followed by LC-QToF-MS detection

The presence of pharmaceutically active compounds (PhACs) in aquatic biota has been received much less attention than their presence in surface or waste water, and it was not until the mid-2000s, this gap started to be addressed. Here, we present SQUEEZe (Solid-liQuid Ultrasound Extraction with QuE Z-Sep/C18 as dispersive clean-up): a fast method for analysis of the trace 47 PhACs in fish muscle. Compared to our previously reported method [1], it offers alternatives with improvements in recoveries, number of analytes, sample volume and solvent used. The key aspects of this method are:•The ultrasound extraction was performed with acetonitrile/isopropanol 0.1% V/V formic acid. A clean-up step using QuE Z-Sep/C18 sorbents was employed to reduce lipid content of the extracts and further matrix effects in the detection of the analytes.•A HPLC separation with a Kinetex EVO C18 packed column in 11 min was optimized. MS and MS/MS data were collected using SWATH acquisition on the SCIEX X500R QTOF in (+)-ESI mode.•The method validated at 3 different concentrations levels: 5, 25 and 50 ng/g fish. It presented good intraday/interday reproducibility and absolute recoveries ≥ 60% for majority of analytes in composite homogenate muscle matrix of Squalius cephalus.•10 out 47 compounds were detected in fish samples.

Electron Ionization Mass Spectrometry for Both Liquid and Gas Chromatography in One System without the Need for Hardware Adjustments

A new instrument that bridges the gap between gas chromatography (GC) and liquid chromatography (LC) mass spectrometry (MS) was developed. In this instrument GC-MS and electron ionization LC-MS were combined in one MS system with method based mode changing. The LC pneumatic spray formation interface to MS was mounted on top of an otherwise unused GC detector slot and was connected with a flow restriction capillary to the MS through the GC oven and into the MS transfer line, parallel to the GC capillary column. The LC output mobile phase flow is directed into a spray formation and vaporization chamber. The pneumatic spray results in fine spray droplets that are thermally vaporized at a pressure equal to or greater than ambient. A portion of the vaporized mixture is directed into the heated flow restriction capillary that connects the spray formation and vaporization chamber into the electron ionization (EI) ion source, while most of the vaporized spray is released to the atmosphere. The combined GC-MS and LC-MS system can work either with standard EI or with cold EI via interfacing the flow restriction capillary into a supersonic nozzle forming a supersonic molecular beam of a vibrationally cold sample compound. We found that EI-LC-MS with cold EI has many benefits when compared with standard EI. The EI-LC-MS interface can also serve for flow injection analysis. The performance of the combined system is demonstrated in the analysis of a few sample mixtures by both GC-MS and LC-MS analysis, sequentially without hardware adjustments.

Selective pressurized liquid extraction of plant secondary metabolites: Convallaria majalis L. as a case

A fast and efficient selective pressurized liquid extraction (sPLE) method was developed to extract secondary metabolites from complex plant matrix. Convallaria majalis L., a plant producing toxic steroids, was used as proof-of-concept. The method was optimized in the aspects of preheating, dispersant, extraction temperature and solvent, and the use of C18 as in-cell cleanup sorbent. Eight authentic natural steroids with diverse sugar moieties and hydrophobicities were selected as reference analytes and spiked to 0.1 g dried leaves. The extraction performance was evaluated based on the analytes' stability, recovery, matrix effect in the electrospray interface and the level of co-extractives. With the optimal method, the extraction was finished in 10 min. A colorless extract was obtained with recoveries ranging from 63% to 107% and absolute matrix effects ranging from 3% to 27%. The optimized method was validated by extracting 0.1 g, 0.2 g and 0.4 g spiked plant samples; method accuracy and precision were assessed by recoveries and relative standard deviations of the combined extraction-analysis workflow. The method was also tested on soil samples and indicated its suitability for measuring secondary metabolites in multiple environmental matrices. To our knowledge, this is the first time sPLE has been reported to extract plant secondary metabolites from a complex plant matrix, with satisfactory recoveries and low matrix effects. This is also the first time (s)PLE has been reported to extract plant secondary metabolites from soil. We envision the method be coupled with liquid chromatography-electrospray ionization-high resolution mass spectrometry in a standard metabolomics workflow to facilitate plant metabolomics studies.

Current developments in LC-MS for pharmaceutical analysis

Liquid chromatography (LC) based techniques in combination with mass spectrometry (MS) detection have had a large impact on the development of new pharmaceuticals in the past decades.

Quenchers in advanced oxidation technologies for analysis of micropollutants by liquid chromatography coupled to mass spectrometry: Sodium sulphite or catalase?

This work aimed to investigate the possible effect of 2 quenchers commonly used in H₂O₂-based advanced oxidation technologies (AOTs), i.e. catalase and sodium sulphite (Na₂SO₃), on the analytical signal of 3 detectors coupled to liquid chromatography (LC): tandem mass spectrometry (LC-MS/MS), fluorescence detection (LC-FD) and LC-diode array detection (LC-DAD). The observation of analytical interferences for a group of compounds when studying the removal by continuous mode UV/H₂O₂ of 26 micropollutants (MPs) from a spiked surface water (SW), for which the residual H₂O₂ in the samples was quenched by Na₂SO₃, triggered the need of understanding these effects and thus catalase was used as comparative quencher. From the 26 MPs having a wide range of polarity and pK_a, those monitored after electrospray ionization (ESI) under positive ionization (PI) mode and presenting a pK_a higher than 5.9 revealed a great signal suppression, but only when using Na₂SO₃ as H₂O₂ quencher. In this sense, we further explored this effect by selecting 2 MPs, metoprolol and diclofenac, which had respectively signal suppression and no interference in the LC-MS/MS response. These MPs were analysed before and after addition of H₂O₂ and catalase or Na₂SO₃ in reaction vials, using: (i) different detectors coupled to LC, namely LC-MS/MS with ESI under PI and negative ionization (NI) modes, LC-FD and LC-DAD; (ii) different environmental matrices (SW, drinking water, wastewater) and ultrapure water; and (iii) different magnitude levels (0.1-10 mg L^-1). The results demonstrated a remarkable signal suppression in LC-MS/MS analyses under PI mode for those compounds with pK_a higher than 5.9, confirming the interfering effect of H₂O₂/Na₂SO₃. To the best of our knowledge, the analytical interference in the LC-MS/MS analysis, after adding Na₂SO₃ to quench H₂O₂ in AOTs experiments was never reported before and the results presented herein support the recommendation to use catalase instead of Na₂SO₃ as quencher in AOTs studies.

Determination of 18 organophosphorus flame retardants/plasticizers in mussel samples by matrix solid-phase dispersion combined to liquid chromatography-tandem mass spectrometry

This study presents the development and validation of a new analytical method based on matrix solid-phase dispersion (MSPD), integrating sample extraction and clean-up in one single step, followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) for the simultaneous determination of 18 organophosphorus flame retardants and/or plasticizers (OPEs) in marine mussel (Mytilus edulis and Mytilus galloprovincialis) samples. Among these OPEs, 5 (tetraethyl 1,2-ethanediylbis(phosphonate), 6H-dibenzo[c,e] [1,2]oxaphosphinine 6-oxide, tris(2,3-dibromopropyl) phosphate, 2,2-propanediyldi-4,1-phenylene bis(phosphate) and resorcinol bis(diphenyl phosphate)) are considered here for the first time in marine samples. Different parameters affecting the MSPD (clean-up sorbent and elution solvent) were optimized to obtain a good compromise between analyte recoveries and extract clean-up. Also, particular attention was paid to tackle blank issues. The overall method was validated in terms of trueness, precision and detection and quantification limits. Percentages of recovery varied from 69% to 122% with relative standard deviations below 24%. Detection limits ranged from 0.06 to 5 ng g^-1 and quantification limits from 0.19 to 17 ng g^-1 dry weight. Finally, the method was applied to the analysis of 7 mussel samples collected in the coast of Galicia (Spain). 8 OPEs were detected in these samples at concentrations ranging from the LOQ to 291 ng g^-1 dry weight.

Paradigm Shift in the Arena of Sample Preparation and Bioanalytical Approaches Involving Liquid Chromatography Mass Spectroscopic Technique

Sample preparation is a highly important and integral part of bioanalysis for cleaning up the complex biological matrices and thereby minimizing matrix effect. Matrix effect can jeopardize the precise quantification and adversely affect the reliability of liquid chromatography-mass spectrometry-based analytical results by alteration of analyte ionization. Matrix components result in suppression or enhancement of the intensity of analyte response. In spite of the high specificity and selectivity of tandem mass spectrometry, a relatively higher concentration of coeluted matrix elements present in biofluids may alter the efficiency of quantification of a bioanalytical method. Numerous literature reports different types of sample preparation techniques employed in bioanalysis. In this review, the strategies for selection of the appropriate sample clean-up technique in bioanalysis are discussed extensively. A paradigm shift in the arena of sample preparation and bioanalytical approaches involving the liquid chromatography-mass spectroscopic technique has been scrutinized. Current trends and possible future advancements in the field of biological sample extraction methods, including instrumental techniques are analyzed in detail.

An improved extraction protocol for therapeutic dabigatran monitoring using HPLC-MS/MS

A new sample extraction protocol was developed for pharmacokinetic studies of dabigatran with high-performance liquid chromatography separation - electrospray ionization time-of-flight mass spectrometry analysis. After protein precipitation with acetonitrile, free dabigatran and its metabolites are separated into water phase by water-dichloromethane liquid-liquid extraction to purify the sample from proteins and endogenous lipophilic compounds. Chromatographic separation was achieved on an Agilent Zorbax SB-CN column (150 × 4.6 mm, 5 µm)) using 0.1% aqueous solution of formic acid and acetonitrile (80:20) as the mobile phase. Agilent Zorbax SB-CN column was selected to improve sample resolution and to avoided early elution of dabigatran previously seen when using a C18 column. The extended calibration curve was constructed from 5 to 1000 ng/L while precision and accuracy were assessed at four levels across the linear dynamic ranges. Within-run precision was <5.6% and the between-run precision was <3.9%. The method accuracy ranged from 89.8% to 104.4%. The developed method was successfully applied to 30 patient samples to evaluate antithrombotic efficacy and anticoagulant activity of dabigatran following knee endoprosthesis surgery.

Development and validation of an analytical method for determination of pharmaceuticals in fish muscle based on QuEChERS extraction and SWATH acquisition using LC-QTOF-MS/MS system

This study aimed at developing an analytical method for the extraction and quantification of 21 pharmaceutical actives compounds (PhACs) present in fish muscle. Using Norwegian Atlantic salmon as matrix, two extraction methods for PhACs were tested: ultrasound extraction (USE) using methanol (MeOH), acetonitrile (MeCN) or a mixture of MeCN:MeOH (1:1, v/v) as extracting solvents, and QuEChERS method using three different extraction salts. After selecting QuEChERS Original as extracting method of the analytes, three different clean-up methods were evaluated with respect to their efficiency to remove coextracted fat and lipids such as Enhanced Matrix Removal (EMR) and HLB prime. The dispersive-SPE EMR yielded the best recoveries for 21 of 27 analytes. PhACs were quantified by UPLC-MS/MS using SWATH acquisition mode. The method was validated in terms of recoveries, accuracy, linearity, precision, matrix effects at three levels of concentration: 25, 200 and 500 ng g^-1 dw of fish muscle. For the majority of the analytes the recoveries were over 70%. Finally, the validated method was applied to natural riverine fish from the Evrotas river (Greece) and the Adige river (Italy) with positive findings for acetaminophen, propranolol, and venlafaxine reaching concentrations as high as 80 ng g^-1 of muscle.

Evaluation of a liquid electron ionization liquid chromatography-mass spectrometry interface

Liquid Electron Ionization (LEI), is an innovative liquid chromatography-mass spectrometry (LC-MS) interface that converts liquid HPLC eluent to the gas-phase in a mass spectrometer equipped with an electron ionization (EI) source. LEI extends the electronic spectra libraries access to liquid chromatography, providing a powerful tool in the untargeted approacssh. Negligible matrix effects allow accurate quantitative information. The purpose of this research was to evaluate the main aspects concerning the interfacing process. These fundamental studies were necessary to understand the mechanism of LEI in details, and improve the interfacing process, especially regarding robustness and sensitivity. Hardware components were installed to prevent analytes precipitation, reduce thermal decomposition of sensitive compounds, and to stabilize the nano-flow delivery with different mobile-phase compositions. Particular attention was devoted to insulating the heated vaporization area from the LC part of the system. Experiments were performed to optimize the interface inner capillary dimensions, and other operative parameters, including temperature, gas and liquid flow rates. Test compounds of environmental interest were selected based on molecular weight, thermal stability, volatility, and polarity. Robustness was evaluated with a set of replicated injections and calibration experiments using a soil matrix as a test sample. MRM detection limits in the low-picogram range were obtained for five pesticides belonging to different classes in a soil sample. High-quality electron ionization mass spectra of a mixture of pesticides were also obtained.

Grape and Wine Metabolomics to Develop New Insights Using Untargeted and Targeted Approaches

Chemical analysis of grape juice and wine has been performed for over 50 years in a targeted manner to determine a limited number of compounds using Gas Chromatography, Mass-Spectrometry (GC-MS) and High Pressure Liquid Chromatography (HPLC). Therefore, it only allowed the determination of metabolites that are present in high concentration, including major sugars, amino acids and some important carboxylic acids. Thus, the roles of many significant but less concentrated metabolites during wine making process are still not known. This is where metabolomics shows its enormous potential, mainly because of its capability in analyzing over 1000 metabolites in a single run due to the recent advancements of high resolution and sensitive analytical instruments. Metabolomics has predominantly been adopted by many wine scientists as a hypothesis-generating tool in an unbiased and non-targeted way to address various issues, including characterization of geographical origin (terroir) and wine yeast metabolic traits, determination of biomarkers for aroma compounds, and the monitoring of growth developments of grape vines and grapes. The aim of this review is to explore the published literature that made use of both targeted and untargeted metabolomics to study grapes and wines and also the fermentation process. In addition, insights are also provided into many other possible avenues where metabolomics shows tremendous potential as a question-driven approach in grape and wine research.

Suitable simple and fast methods for selective isolation of phospholipids as a tool for their analysis

Lipids are gaining relevance over the last 20 years, as our knowledge about their role has changed from merely energy/structural molecules to compounds also involved in several biological processes. This led to the creation in 2003 of a new emerging research field: lipidomics. In particular the phospholipids have pharmacological/food applications, participate in cell signalling/homeostatic pathways while their analysis faces some challenges. Their fractionation/purification is, in fact, especially difficult, as they are amphiphilic compounds. Moreover, it usually involves SPE or TLC procedures requiring specific materials hampering their suitableness for routine analysis. Finally, they can interfere with the ionization of other molecules during mass spectrometry analysis. Thus, simple high-throughput reliable methods to selectively isolate these compounds based on the difference between chemical characteristics of lipids would represent valuable tools for their study besides that of other compounds. The current review work aims to describe the state-of-the-art related to the extraction of phospholipids using liquid-liquid methods for their targeted isolation. The technological and biological importance of these compounds and ion suppression phenomena are also reviewed. Methods by precipitation with acetone or isolation using methanol seem to be suitable for selective isolation of phospholipids in both biological and food samples.

Integration of Metabolomics and Transcriptomics Reveals a Complex Diet of Mycobacterium tuberculosis during Early Macrophage Infection

The nutrients consumed by intracellular pathogens are mostly unknown. This is mainly due to the challenge of disentangling host and pathogen metabolism sharing the majority of metabolic pathways and hence metabolites. Here, we investigated the metabolic changes of Mycobacterium tuberculosis, the causative agent of tuberculosis, and its human host cell during early infection. To this aim, we combined gene expression data of both organisms and metabolite changes during the course of infection through integration into a genome-wide metabolic network. This led to the identification of infection-specific metabolic alterations, which we further exploited to model host-pathogen interactions quantitatively by flux balance analysis. These in silico data suggested that tubercle bacilli consume up to 33 different nutrients during early macrophage infection, which the bacteria utilize to generate energy and biomass to establish intracellular growth. Such multisubstrate fueling strategy renders the pathogen’s metabolism robust toward perturbations, such as innate immune responses or antibiotic treatments.

Nutrient acquisition from the host environment is crucial for the survival of intracellular pathogens, but conceptual and technical challenges limit our knowledge of pathogen diets. To overcome some of these technical roadblocks, we exploited an experimentally accessible model for early infection of human macrophages by Mycobacterium tuberculosis, the etiological agent of tuberculosis, to study host-pathogen interactions with a multi-omics approach. We collected metabolomics and complete transcriptome RNA sequencing (dual RNA-seq) data of the infected macrophages, integrated them in a genome-wide reaction pair network, and identified metabolic subnetworks in host cells and M. tuberculosis that are modularly regulated during infection. Up- and downregulation of these metabolic subnetworks suggested that the pathogen utilizes a wide range of host-derived compounds, concomitant with the measured metabolic and transcriptional changes in both bacteria and host. To quantify metabolic interactions between the host and intracellular pathogen, we used a combined genome-scale model of macrophage and M. tuberculosis metabolism constrained by the dual RNA-seq data. Metabolic flux balance analysis predicted coutilization of a total of 33 different carbon sources and enabled us to distinguish between the pathogen’s substrates directly used as biomass precursors and the ones further metabolized to gain energy or to synthesize building blocks. This multiple-substrate fueling confers high robustness to interventions with the pathogen’s metabolism. The presented approach combining multi-omics data as a starting point to simulate system-wide host-pathogen metabolic interactions is a useful tool to better understand the intracellular lifestyle of pathogens and their metabolic robustness and resistance to metabolic interventions.

IMPORTANCE The nutrients consumed by intracellular pathogens are mostly unknown. This is mainly due to the challenge of disentangling host and pathogen metabolism sharing the majority of metabolic pathways and hence metabolites. Here, we investigated the metabolic changes of Mycobacterium tuberculosis, the causative agent of tuberculosis, and its human host cell during early infection. To this aim, we combined gene expression data of both organisms and metabolite changes during the course of infection through integration into a genome-wide metabolic network. This led to the identification of infection-specific metabolic alterations, which we further exploited to model host-pathogen interactions quantitatively by flux balance analysis. These in silico data suggested that tubercle bacilli consume up to 33 different nutrients during early macrophage infection, which the bacteria utilize to generate energy and biomass to establish intracellular growth. Such multisubstrate fueling strategy renders the pathogen’s metabolism robust toward perturbations, such as innate immune responses or antibiotic treatments.

Inter-laboratory skin distribution study of 4-n-butyl resorcinol: The importance of liquid chromatography/mass spectrometry (HPLC-MS/MS) bioanalytical validation

In the present study, three laboratories independently compared percutaneous absorption and distribution of 4-n-butylresorcinol, using human skin from five donors. Each laboratory used the same protocol for percutaneous absorption studies but different LC-MS/MS analytical methods to quantify the test compound. All laboratories respected the mass balance criteria (i.e. 100±15%; average 96.5-102% of applied dose). Regarding usual inter-lab variability, good agreement was observed for all compartments with the greatest difference in the epidermis: 3.3 fold increase. The data obtained demonstrate that robustness of skin absorption data rely on properly validated analytical methods including sample extraction and LC-MS/MS method. It also includes clearly defined cutaneous absorption protocol for dose skin preparation, application, washing and tape stripping.

Atmospheric Pressure Vaporization Mechanism for Coupling a Liquid Phase with Electron Ionization Mass Spectrometry

A novel liquid chromatography-mass spectrometry (LC-MS) interfacing concept is presented and discussed. The new interface, called liquid-EI (LEI), is based on electron ionization (EI) but, differently from any previous attempt, the vaporization of solutes and mobile phase takes place at atmospheric pressure into a specifically designed region, called "vaporization microchannel", before entering the high-vacuum ion source. The interface is completely independent from the rest of the instrumentation and can be adapted to any gas chromatography/mass spectrometry (GC/MS) system, as an add-on for a rapid LC-MS conversion. Pressure drop and temperature gradient between LC and MS were considered to enhance the analyte response and reduce band broadening and/or solute carryovers. A fused silica liner, placed inside the vaporization microchannel, acts as an inert vaporization surface speeding up the gas-phase conversion of large molecules while lessening possible memory effects. The liner is easily replaceable for a quick and extremely simple interface maintenance. Proof of concept and detailed description of the interface are here presented.

Electron ionization LC-MS with supersonic molecular beams--the new concept, benefits and applications

A new type of electron ionization LC-MS with supersonic molecular beams (EI-LC-MS with SMB) is described. This system and its operational methods are based on pneumatic spray formation of the LC liquid flow in a heated spray vaporization chamber, full sample thermal vaporization and subsequent electron ionization of vibrationally cold molecules in supersonic molecular beams. The vaporized sample compounds are transferred into a supersonic nozzle via a flow restrictor capillary. Consequently, while the pneumatic spray is formed and vaporized at above atmospheric pressure the supersonic nozzle backing pressure is about 0.15 Bar for the formation of supersonic molecular beams with vibrationally cold sample molecules without cluster formation with the solvent vapor. The sample compounds are ionized in a fly-though EI ion source as vibrationally cold molecules in the SMB, resulting in 'Cold EI' (EI of vibrationally cold molecules) mass spectra that exhibit the standard EI fragments combined with enhanced molecular ions. We evaluated the EI-LC-MS with SMB system and demonstrated its effectiveness in NIST library sample identification which is complemented with the availability of enhanced molecular ions. The EI-LC-MS with SMB system is characterized by linear response of five orders of magnitude and uniform compound independent response including for non-polar compounds. This feature improves sample quantitation that can be approximated without compound specific calibration. Cold EI, like EI, is free from ion suppression and/or enhancement effects (that plague ESI and/or APCI) which facilitate faster LC separation because full separation is not essential. The absence of ion suppression effects enables the exploration of fast flow injection MS-MS as an alternative to lengthy LC-MS analysis. These features are demonstrated in a few examples, and the analysis of the main ingredients of Cannabis on a few Cannabis flower extracts is demonstrated. Finally, the advantages of EI-LC-MS with SMB are listed and discussed.

Optimisation and validation of analytical methods for the simultaneous extraction of antioxidants: application to the analysis of tomato sauces

In the present study, simultaneous extraction of natural antioxidants (phenols and carotenoids) in complex matrices, such as tomato sauces, is presented. The tomato sauce antioxidant compounds studied were the phenolics hydroxytyrosol, from virgin olive oil, quercetin and its derivatives, from onions, and quercetin-rutinoside as well as the carotenoid, lycopene (cis and trans), from tomatoes. These antioxidant compounds were extracted simultaneously with n-hexane/acetone/ethanol (50/25/25, v/v/v). The phenolics were analysed by ultra-performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS), and lycopene (cis- and trans-forms) was analysed using high-performance liquid chromatography coupled to a diode array detector (HPLC-DAD). After studying the parameters of these methods, they were applied to the analysis of virgin olive oil, fresh onion, tomato concentrate and tomato powder, and commercial five tomato sauces. Subsequently, the results obtained in our laboratory were compared with those from the Gallina Blanca Star Group laboratory.

Signal suppression can bias selected reaction monitoring ratios. Implications for the confirmation of positive findings in residue testing

RATIONALE

Selected reaction monitoring (SRM) ratios based on two or more transitions are commonly used to confirm the identity of a suspected finding in residue testing. International norms like the EU directive commission decision 2002/657/EC (CD) require the use of such ratios to prove the unequivocal identification of a particular compound detected at trace level (confirmation of a suspected residue).

METHODS

In this study, the relative abundances of different precursor ions (e.g. protonated molecule, solvent adducts, characteristic fragment ions or multiply charged ions) derived from the same analyte molecule were found to be differently (asymmetrically) affected by matrix-related signal suppression effects. This observation was made when analyzing veterinary drug residues (colistin and amoxicillin) in animal tissue extracts.

RESULTS

The term 'asymmetric signal suppression' was coined since different ionic species produced from the same analyte molecule are differently (asymmetrically) suppressed by co-eluting matrix compounds. In the case of the colistin assay, the extent of asymmetric signal suppression is such that the measured SRM ratios lie beyond the defined (CD) tolerances. Hence, the compound present in a sample cannot be confirmed.

CONCLUSIONS

The [M+H](+) ion may be the most commonly used precursor ion in liquid chromatography coupled to electrospray operated in the positive ionization mode. However, the absence of a sufficiently intensive confirmation transition frequently leads to the selection of another precursor ion to be utilized for the confirmation transition. The SRM ratio derived from such transitions should not be compared to the SRM ratio derived from pure standard solutions but spiked blank matrix extracts.

Analytical considerations on the use of a fruit-specific and representative matrix in pesticide residue analysis by LC-ESI-MS/MS

One of the quantification methods frequently applied to pesticide residue analysis in food by liquid chromatography — mass spectrometry (LC-MS) involves matrix-matched calibrations with a representative matrix used for all commodities belonging to one group. This approach, although very practical, is deemed to generate analytical errors. The effect of the application of a representative-matrix calibration curve on the pesticide quantification result was examined. Extractions of 56 pesticides from five soft fruits (strawberries, blackberries, raspberries, black currant and red currant) were carried out using QuEChERS method. Pesticide determinations were performed by LC-MS/MS in multiple reaction monitoring mode. Quantification difference functions and parameters were proposed and calculated. At the concentration of 0.05 mg kg−1 for ca. 90% of examined pesticides the quantification difference arising from the use of a representative matrix calibration curve (raspberries) instead of a specific fruit matrix calibration curve was below 20% for black and red currents, and below 30% and 35% in the case of strawberries and blackberries, respectively. The 25% difference limit was not exceeded for 51 pesticides in black and red currents, 46 pesticides in blackberries and 45 pesticides in strawberries. Quantification difference functions and parameters such as relative standard deviation of corrected process efficiencies were found to be helpful in data-driven decision-making on the applicability of a representative matrix; the former may be also used as a tool for data correction to ensure the reliability and accuracy of analyses.