Direct extract derivatization for determination of amino acids in human urine by gas chromatography and mass spectrometry

Spectroscopic Study of a Novel Binaphthyl Amine Fluorescent Probe for Chiral Recognition of D/L-Lysine

Lysine plays a crucial role in promoting development, enhancing immune function, and improving the function of central nervous system tissues. The two configurational isomers of amino acids have significantly different effects. Currently, methods for chiral recognition of lysine have been reported; however, previous detection methods have drawbacks such as expensive equipment and complicated detection processes. Fluorescence analysis, on the other hand, boasts high sensitivity, strong selectivity, and simple operation. In this study, we synthesized four novel Binaphthyl-Amine (BINAM)-based fluorescent probes capable of specifically identifying the L-configuration of lysine among the twenty amino acids that constitute human proteins. The enantiomeric fluorescence enhancement ratio (ef or ΔIL/ΔID) reached up to 15.29, demonstrating high enantioselectivity. In addition, we assessed the probe's recognition capabilities under varying pH levels, reaction times, and metal ion conditions, along with its limit of detection (LOD) and quantum yield. Our results suggest that this probe serves as a highly stable tool for the detection of chiral lysine.

Preparation of fluorescein-modified polymer dots and their application in chiral discrimination of lysine enantiomers

Fluorescein-functionalized fluorescent polymer dots (F-PDs) were prepared by a facile one-pot method by magnetic stirring under mild conditions based on carboxymethylcellulose (CMC) and fluorescein as the precursors. The obtained F-PDs exhibited a nanoscale size of 3.2 ± 1.1 nm, excellent water solubility, and bright yellow fluorescence emission with a fluorescence quantum yield of 12.0%. The fluorescent probe displays rapid and sensitive chiral discrimination for lysine focused on different complexation abilities between lysine enantiomers and Cu²⁺. The concentration of L-lysine in the range 4 to 14 mM (R² = 0.997) was measured by the fluorescence intensity ratio (I₅₁₃/I₄₂₉); the exitation wavelength was set to λ_ex = 365 nm. The detection limit was 0.28 mM (3σ/slope). Importantly, this sensor accurately predicted the enantiomeric excess (ee) of lysine enantiomers at the designed concentration (lysine: 20 mM; Cu²⁺: 10 mM) ranges. The proposed sensor was successfully applied to determine L-lys (recovery: 95.8-101%; RSD: 0.465-3.34%) and ee values (recovery: 98.5-102%; RSD: 2.61-3.21%) in human urine samples using the standard addition method.

Nutrient composition of Chenopodium formosanum Koidz. bran: Fractionation and bioactivity of its soluble active polysaccharides

Background

Chenopodium formosanum Koidz. Amaranthaceae-also known as Djulis or red quinoa (RQ)-is a cereal plant indigenous to Taiwan, known for its high nutrient value. However, its bran is considered a waste product and the nutrient value has never been analyzed.

Methods

In this study, we examined the proximate composition of RQ bran, specifically its soluble polysaccharide fractions.

Results

RQ bran exhibited high contents of protein (16.56%), ash (7.10%), carbohydrate (60.45%), total polyphenolics (1.85%), betaxanthin (9.91 mg/100 g of RQ bran), and indicaxanthin (7.27 mg/100 g of RQ bran). Specifically, it was rich in polyunsaturated fatty acids (PUFAs; 39.24%)-with an n-6/n-3 and PUFA/saturated fatty acid (SFA) ratio of 18.137 and 0.743, respectively. Four soluble polysaccharide fractions were also obtained: CF-1, CF-2, CF-3, and CF-4, with yields of 3.90%, 6.74%, 22.28%, and 0.06%, respectively, and molecular weights of 32.54, 24.93, 72.39, and 55.45 kDa, respectively. CF-1, CF-2, CF-3, and CF-4 had respectively 15.67%, 42.41%, 5.44%, and 14.52% peptide moiety content and 38.92%, 50.70%, 93.76%, and 19.80% carbohydrate moiety. In CF-2, the glucose content was 95.86 mol% and that of leucine was 16.23%, implicating the presence of a typical leucinoglucan. All four polysaccharide fractions lacked glutamic acid and hydroxyproline. The IC50 of CF-1, CF-2, and CF-3 was respectively 12.05, 3.98, and 14.5 mg/mL for DPPH free radical-scavenging ability; 5.77, 4.10, and 7.03 mg/mL for hydrogen peroxide-scavenging capability; 0.26, 0.05, and 0.19 mg/mL for O₂ ^- free radical-scavenging capability; and 100.41, 28.12, and 29.73 mg/mL for Fe²⁺ chelation.

Conclusion

Our results indicated that RQ bran has a large amount of nutrient compounds, and a cost-efficient process for their extraction is needed. Their biomedical application as nutraceuticals also warrants further investigation.

Combination of ultrasound-assisted ethyl chloroformate derivatization and switchable solvent liquid-phase microextraction for the sensitive determination of l-methionine in human plasma by GC-MS

A green and fast analytical method for the determination of l-methionine in human plasma is presented in this study. Preconcentration of the analyte was carried out by switchable solvent liquid phase microextraction after ethyl chloroformate derivatization reaction. Instrumental detection of the analyte was performed by means of gas chromatography-mass spectrometry. N,N-Dimethyl benzylamine was used in the synthesis of switchable solvent. Protonated N,N-dimethyl benzylamine volume, volume/concentration of sodium hydroxide, and vortex period were meticulously fixed to their optimum values. Besides, ethyl chloroformate, pyridine, and ethanol volumes were optimized in order to get high derivatization yield. After the optimization studies, limit of detection and quantitation values were attained as 3.30 and 11.0 ng/g, respectively, by the developed switchable solvent liquid phase microextraction gas chromatography-mass spectrometry method that corresponding to 76.7-folds enhancement in detection power of the gas chromatography-mass spectrometry system. Applicability and accuracy of the switchable solvent liquid phase microextraction-gas chromatography-mass spectrometry method were also checked by spiking experiments. Percent recovery results were ranged from 97.8 to 100.5% showing that human plasma samples could be analyzed for its l-methionine level by the proposed method.

Concentration determination of urinary metabolites of N,N-dimethylacetamide by high-performance liquid chromatography-tandem mass spectrometry

OBJECTIVES

N,N-Dimethylacetamide (DMAC) is widely used in industry as a solvent. It can be absorbed through human skin. Therefore, it is necessary to determine exposure to DMAC via biological monitoring. However, the precision of traditional gas chromatography (GC) is low due to the thermal decomposition of metabolites in the high-temperature GC injection port. To overcome this problem, we have developed a new method for the simultaneous separation and quantification of urinary DMAC metabolites using liquid chromatography-tandem mass spectrometry (LC-MS/MS).

METHODS

Urine samples were diluted 10-fold in formic acid, and 1-μl aliquots were injected into the LC-MS/MS equipment. A C18 reverse-phase Octa Decyl Silyl (ODS) column was used as the analytical column, and the mobile phase consisted of a mixture of methanol and aqueous formic acid solution.

RESULTS

Urinary concentrations of DMAC and its known metabolites (N-hydroxymethyl-N-methylacetamide (DMAC-OH), N-methylacetamide (NMAC), and S- (acetamidomethyl) mercapturic acid (AMMA) ) were determined in a single run. The dynamic ranges of the calibration curves were 0.05-5 mg/l (r≥0.999) for all four compounds. The limits of detection for DMAC, DMAC-OH, NMAC, and AMMA in urine were 0.04, 0.02, 0.05, and 0.02 mg/l, respectively. Within-run accuracies were 96.5%-109.6% with relative standard deviations of precision being 3.43%-10.31%.

CONCLUSIONS

The results demonstrated that the proposed method could successfully quantify low concentrations of DMAC and its metabolites with high precision. Hence, this method is useful for evaluating DMAC exposure. In addition, this method can be used to examine metabolite behaviors in human bodies after exposure and to select appropriate biomarkers.

Development and validation of an ultra-performance liquid chromatography quadrupole time of flight mass spectrometry method for rapid quantification of free amino acids in human urine

An ultra-performance liquid chromatography quadrupole time of flight mass spectrometry (UPLC-qTOF-MS) method using hydrophilic interaction liquid chromatography was developed and validated for simultaneous quantification of 18 free amino acids in urine with a total acquisition time including the column re-equilibration of less than 18 min per sample. This method involves simple sample preparation steps which consisted of 15 times dilution with acetonitrile to give a final composition of 25 % aqueous and 75 % acetonitrile without the need of any derivatization. The dynamic range for our calibration curve is approximately two orders of magnitude (120-fold from the lowest calibration curve point) with good linearity (r (2) ≥ 0.995 for all amino acids). Good separation of all amino acids as well as good intra- and inter-day accuracy (<15 %) and precision (<15 %) were observed using three quality control samples at a concentration of low, medium and high range of the calibration curve. The limits of detection (LOD) and lower limit of quantification of our method were ranging from approximately 1-300 nM and 0.01-0.5 µM, respectively. The stability of amino acids in the prepared urine samples was found to be stable for 72 h at 4 °C, after one freeze thaw cycle and for up to 4 weeks at -80 °C. We have applied this method to quantify the content of 18 free amino acids in 646 urine samples from a dietary intervention study. We were able to quantify all 18 free amino acids in these urine samples, if they were present at a level above the LOD. We found our method to be reproducible (accuracy and precision were typically <10 % for QCL, QCM and QCH) and the relatively high sample throughput nature of this method potentially makes it a suitable alternative for the analysis of urine samples in clinical setting.

Determination of proline in human serum by a robust LC-MS/MS method: application to identification of human metabolites as candidate biomarkers for esophageal cancer early detection and risk stratification

Altered serum proline levels are related to cancer metabolism. This study developed and validated a LC-MS/MS method to analyze proline in human serum. Surrogate blank serum, coupled with stable isotope l-proline-(13) C5 ,(15)  N as internal standard, was used for generating standard curves ranging from 2.5 to 100 μg/mL. Proline was extracted from serum samples using methanol. A Phenomenex Lux 5u Cellulose-1 column (250 × 4.6 mm) was used for chromatographic separation with 40% methanol in 0.05% formic acid aqueous solution as a mobile phase. Mass detection was performed under positive ionization electrospray. Intra- and inter-day accuracy and precision were <10%. The extraction recovery and matrix factor were 99.17 and 1.47%, respectively. Our study showed that the chiral column had high specificity and selectivity for separating proline from serum components. The assay was successfully applied for the quantification of human serum proline levels from 30 esophageal cancer patients and 30 healthy volunteers. Statistical analyses showed significantly lower levels of serum proline in the patients as compared with the healthy volunteers (p-value = 0.011). We report here a simple, specific and reproducible LC-MS/MS method for the quantification of proline in human serum as a potential screening biomarker for esophageal cancer.

Mass spectrometry of analytical derivatives. 1. Cyanide cations in the spectra of N- alkyl-N-perfluoroacyl- α-amino acids and their methyl esters

The central mission for the development of the National Institute of Standards and Technology/National Institutes of Health/Environmental Protection Agency Mass Spectral Library is the acquisition of reference gas chromatography-mass spectrometry data for important compounds and their chemical modification products. The addition of reliable reference data of various derivatives of amino acids to The Library, and the study of their behavior under electron ionization conditions may be useful for their identification, structure elucidation and a better understanding of the data obtained when the same derivatives are subjected to other ionization methods. N-Alkyl-N-perfluoroacyl derivatives of amino acids readily produce previously unreported alkylnitrilium cations of composition [HC≡N-alkyl](+). Homologous [HC≡N-aryl](+) cations are typical for corresponding N-aryl analogs. The formation of other ions characteristic for these derivatives involves oxygen rearrangement giving rise to ions [C(n)F(2n+1)-C≡N(+)C(n)H(2n+1)] and [CnF(2n+1)-C≡N(+)-aryl]. The introduction of an N-benzyl substituent in a molecule favors a process producing benzylidene iminium cations. L-Threonine and L-cysteine derivatives exhibit more fragmentation pathways not typical for other α-amino acids; additionally, the N(ω)- amino group in L-lysine directs the dissociation process and provides structural information on the substitution at the amino functions in the molecule.

Use of UPLC-ESI-MS/MS to quantitate free amino acid concentrations in micro-samples of mammalian milk

Although free amino acids (FAA) account for a small fraction of total nitrogen in mammalian milk, they are more abundant in human milk than in most formulas, and may serve as a readily available source of amino acids for protein synthesis, as well as fulfill specific physiologic roles. We used reversed phase Ultra Performance Liquid Chromatography (UPLC) coupled to electrospray ionization tandem mass spectrometry (ESI-MS/MS) technique for FAA profiling in milks from three species (human, rat and cow) with a simple and rapid sample preparation. The derivatization procedure chosen, combined with UPLC-ESI-MS/MS allowed the quantitation of 21 FAA using labeled amino acids (Internal Standards) over a 10 min run time in micro-samples of mammalian milk (50 μL). The low limit of quantitation was 0.05 pmol/μL for most FAA with good repeatability and reproducibility (mean CV of 5.1%). Higher levels of total FAA were found in human (3032 μM) and rat milk (3460 μM) than in bovine milk (240 μM), with wide differences in the abundances of specific FAA between species. This robust analytical method could be applied to monitor FAA profile in human breast milk, and open the way to individualized adjustment of FAA content for the nutritional management of infants.

An electrochemical aptasensor based on the amplification of two kinds of gold nanocrystals for the assay of L-histidine with picomolar detection limit

Au nanocrystals (NCs) enclosed by higher-index facets have high surface chemical activity. They attract much attention because of their excellent biocompatibility. In this work, well-defined elongated tetrahexahedral (ETHH) Au NCs and end-truncated ETHH with high-index facets are successfully prepared by using a single surfactant system of didodecyldimethylammonium bromide (DDAB) and a binary system of cetyltrimethylammoniumbromide and DDAB in two-step seed-mediated growth. The characteristics of high-index facet Au NC modified electronic aptamer-based sensors are presented and they are applicable to a wide range of aptamers. Herein, we only take L-histidine as the representative sensing target. With modification of the Au NCs, a very low detection limit (sub-picomolar) is obtained. In particular, a detailed sensitivity comparison between the modification of end-truncated ETHH and ETHH Au NCs is presented to demonstrate the slight difference in the chemical activities of Au NCs with different high-index facets. Our work sheds light on the large scale fabrication of Au/metallic NCs with high-index facets and also provides a new eye-opening example of engineering ultra-sensitive DNA sensors based on Au NCs.

Sarcosine as a marker in prostate cancer progression: a rapid and simple method for its quantification in human urine by solid-phase microextraction-gas chromatography-triple quadrupole mass spectrometry

Sarcosine is an amino acid derivative of N-methylglycine and is involved in the amino acid metabolism and methylation processes that are enriched during prostate cancer progression. It could also serve as a new target to be measured during therapeutic interventions and help in the identification of aggressive tumors for radical treatment. In this study, we present a new urine test that can help early diagnosis of prostate cancer. The method for the quantification of sarcosine in urine consists of a solid-phase microextraction (SPME) step followed by gas chromatography-triple quadrupole mass spectrometry analysis. We used a preliminary derivatization step with ethyl chloroformate/ethanol and the corresponding ester was then extracted by SPME in immersion mode. Several fibers were evaluated and the optimization of the parameters affecting the SPME process was carried out using an experimental design. The optimal values were 20 min extraction time, 10% NaCl, and 270°C using a divinylbenzene/Carboxen/polydimethylsiloxane fiber. The triple quadrupole analyzer acquired data in selected reaction monitoring mode, allowing us to obtain reconstructed chromatograms with well-defined chromatographic peaks. The accuracy and precision of this method were evaluated at concentrations of 70, 250, and 800 ng/ml and were found to be acceptable. Very satisfactory values (0.10 and 0.16 ng/ml, respectively) were also achieved for the limit of detection and the limit of quantification. The proposed protocol represents a rapid, simple, selective, and sensitive tool to quantify sarcosine in urine samples for prostate cancer diagnosis and for a screening test.

Formulation and stability of a novel artificial human sweat under conditions of storage and use

A limitation of most artificial sweat formulations used for in vitro assessment of chemical release from materials in contact with skin have little biological relevance to human sweat. The purposes of this paper are to provide guidance for preparation of a novel artificial sweat with chemical constituents at concentrations that match human sweat and to characterize chemical stability. The artificial sweat was characterized under conditions of use (with and without sebum at 36 degrees C) and storage (without sebum at -4, 4, and 23 degrees C) over 28 days by gas chromatography-mass spectroscopy, high-performance liquid chromatography, enzymatic assay kits, and ion-selective electrodes. Seven indicator constituents were tracked: sodium, chloride, glucose, lactic acid, urea, pantothenic acid, and alanine. With or without sebum at 36 degrees C, the sweat solvent was chemically stable for 14 days. Storage by refrigeration at 4 degrees C retained the chemical integrity of the solvent longest. Based on these results, the solvent should be used within 14 days of preparation. The artificial sweat model presented herein is most similar to human sweat and has applications as a dissolution solvent, donor solution in diffusion cells, or vehicle for patch testing. This sweat model may aid researchers in understanding potential release and percutaneous absorption of chemicals in contact with human skin surface liquids.

Metabolomics study on the anti-depression effect of xiaoyaosan on rat model of chronic unpredictable mild stress

ETHNOPHARMACOLOGY

Xiaoyaosan, a famous Chinese prescription, composed of Poria (Poria cocos (Schw.) Wolf), Radix Paeoniae Alba (Paeonia lactiflora Pall.), Radix Glycyrrhizae (Glycyrrhiza uralensis Fisch.), Radix Bupleuri (Bupleurum chinense DC.), Radix Angelicae Sinensis (Angelica sinensis (Oliv.) Diels), Rhizoma Atractylodis Macrocephalae (Atractylodes macrocephala Koidz.), Herba Menthae (Mentha haplocalyx Briq.), and Rhizoma Zingiberis Recens (Zingiber officinale Rosc.), has been widely used in the clinic for treating mental disorders. Behavior and biochemical analyses indicate xiaoyaosan has obvious anti-depression activity. However, there is no report on the effects of xiaoyaosan using a metabolomics approach.

AIM OF THE STUDY

A urinary metabolomics method was applied to evaluate the efficacy of xiaoyaosan on rat model of chronic unpredictable mild stress.

MATERIAL AND METHODS

Rats were divided into 6 groups and drugs were administered during the 21-day model building period. Urine was measured using GC-MS, processed with XCMS and Microsoft Excel and analyzed by SIMCA-P and SPASS software. Variable importance in projection statistics and loading plot were used to find biomarker ions.

RESULTS

Clear separation between model and each drug group was achieved. High dose group of xiaoyaosan was much closer to control group than middle dose group and amitriptyline group. The time-dependent recovery tendency in high dose group was obtained.

CONCLUSIONS

In term of anti-depression effect, high dose xiaoyaosan was the most effective and amitriptyline equaled middle dose xiaoyaosan as shown by metabolomics strategy and behavior tests. Some common and characteristic metabolites on the anti-depression of xiaoyaosan and amitriptyline were obtained. The work showed metabolomics is a valuable tool in studying the efficacy and potential biomarkers of therapeutic effect of complex prescriptions.

Gas chromatography/atmospheric pressure chemical ionization-time of flight mass spectrometry: analytical validation and applicability to metabolic profiling

Gas Chromatography (GC)-Mass Spectrometry (MS) with Atmospheric Pressure (AP) interface was introduced more than 30 years ago but never became a mainstream technique, mainly because of technical difficulties and cost of instrumentation. A recently introduced multipurpose AP source created the opportunity to reconsider the importance of AP ionization for GC. Here, we present an analytical evaluation of GC/APCI-MS showing the benefits of soft atmospheric pressure chemical ionization for GC in combination with a Time of Flight (TOF) mass analyzer. During this study, the complete analytical procedure was optimized and evaluated with respect to characteristic analytical parameters, such as repeatability, reproducibility, linearity, and detection limits. Limits of detection (LOD) were found within the range from 11.8 to 72.5 nM depending on the type of compound. The intraday and interday repeatability tests demonstrate relative standard deviations (RSDs) of peak areas between 0.7%-2.1% and 3.8%-6.4% correspondingly. Finally, we applied the developed method to the analysis of human cerebrospinal fluid (CSF) samples to check the potential of this new analytical combination for metabolic profiling.

Accurate quantitation of standard peptides used for quantitative proteomics

MS-based proteomics has become an indispensable tool in system biology generating a need for accurate and precise quantitation of peptide standards. The presented method utilizes ultra performance LC-MS/MS (UPLC-MS/MS) to accurately quantify peptide standards at concentrations of 0.1-10 microM. The ability for accurate quantitation of micro-molar concentrations has the advantages that quantitation can be performed routinely with high precision and the high sensitivity of the method minimizes the amounts required.

Gas chromatography-mass spectrometry analysis of pheomelanin degradation products

Melanoma is most rapidly increasing in the white population and people with pheomelanin skin type are at high risk to develop melanoma. However, little is known about the pheomelanin structure and function, and further elucidation of this melanin is therefore an important task. A GC/MS method was developed based on hydriodic acid hydrolysis of pheomelanin in the urine. Derivatization was performed with ethyl chloroformate and ethanol:pyridine (4:1, v/v). N,O-Ethoxycarbonyl-ethyl esters were extracted with chloroform and analyzed by GC/MS. 4-Amino-3-hydroxyphenylalanine and 3-amino-4-hydroxyphenylalanine together with one benzothiazinone and two benzothiazole compounds were detected and identified in hydrolyzed samples of synthetic pheomelanin and melanin from the urine of a patient with melanoma. These findings strongly suggest that heterocyclic pheomelanin-type units are incorporated in the pigment structures.

Automated GC-MS analysis of free amino acids in biological fluids

A gas chromatography-mass spectrometry (GC-MS) method was developed for the quantitative analysis of free amino acids as their propyl chloroformate derivatives in biological fluids. Derivatization with propyl chloroformate is carried out directly in the biological samples without prior protein precipitation or solid-phase extraction of the amino acids, thereby allowing automation of the entire procedure, including addition of reagents, extraction and injection into the GC-MS. The total analysis time was 30 min and 30 amino acids could be reliably quantified using 19 stable isotope-labeled amino acids as internal standards. Limits of detection (LOD) and lower limits of quantification (LLOQ) were in the range of 0.03-12 microM and 0.3-30 microM, respectively. The method was validated using a certified amino acid standard and reference plasma, and its applicability to different biological fluids was shown. Intra-day precision for the analysis of human urine, blood plasma, and cell culture medium was 2.0-8.8%, 0.9-8.3%, and 2.0-14.3%, respectively, while the inter-day precision for human urine was 1.5-14.1%.

Analysis of urinary metabolites for metabolomic study by pressurized CEC

A new approach for the metabolomic study of urinary samples using pressurized CEC (pCEC) with gradient elution is proposed as an alternative chromatographic separation tool with higher degree of resolution, selectivity, sensitivity, and efficiency. The pCEC separation of urinary samples was performed on a RP column packed with C(18), 5 microm particles with an ACN/water mobile phase containing TFA. The effects of the acid modifiers, applied voltage, mobile phase, and detection wavelength were systematically evaluated using eight spiked standards, as well as urine samples. A typical analytical trial of urine samples from Sprague Dawley (S.D.) rats exposed to high-energy diet was carried out following sample pretreatment. Significant differences in urinary metabolic profiles were observed between the high energy diet-induced obesity rats and the healthy control rats at the 6th wk postdose. Multivariate statistical analysis revealed the differential metabolites in response to the diet, which were partially validated with the putative standards. This work suggests that such a pCEC-based separation and analysis method may provide a new and cost-effective platform for metabolomic study uniquely positioned between the conventional chromatographic tools such as HPLC, and hyphenated analytical techniques such as LC-MS.

Determination of 13C isotopic enrichment of valine and threonine by GC–C–IRMS after formation of the N(O,S)-ethoxycarbonyl ethyl ester derivatives of the amino acids

We describe a new method of assessing, in a single run, (13)C isotopic enrichment of both Val and Thr by gas chromatography-combustion-isotope-ratio mass spectrometry (GC-C-IRMS). This method characterised by a rapid one-step derivatisation procedure performed at room temperature to form the N(O,S)-ethoxycarbonyl ethyl ester derivatives, and a polar column for GC. The suitability of this method for Val and Thr in in-vivo samples (mucosal hydrolysate) was demonstrated by studying protein metabolism with two tracers ((13)C-valine or (13)C-threonine). The intra-day and inter-day repeatability were both assessed either with standards or with in-vivo samples at natural abundance and at low (13)C isotopic enrichment. For inter-day repeatability CVs were between 0.8 and 1.5% at natural abundance and lower than 5.5% at 0.112 and 0.190 atom% enrichment for Val and Thr, respectively. Overall isotopic precision was studied for eleven standard amino acid derivatives (those of Val, Ala, Leu, Iso, Gly, Pro, Asp, Thr, Ser, Met, and Phe) and was assessed at 0.32 per thousand. The (13)C isotopic measurement was then extended to the other amino acids (Ala, Val, Leu, Iso, Gly, Pro, Thr, and Phe) at natural abundance for in-vivo samples. The isotopic precision was better than 0.002 atom% per amino acid (for n = 4 rats). This analytical method was finally applied to an animal study to measure Thr utilization in protein synthesis.

Analysis of dencichine in Panax notoginseng by gas chromatography-mass spectrometry with ethyl chloroformate derivatization

Dencichine (beta-N-oxalyl-l-alpha,beta-diaminopropionic acid) is a haemostatic agent present in well-known traditional Chinese medicinal herbs such as Panax notoginseng, as well as other Panax species. It is also a reported neurotoxic agent found in Lathyrus sativus (grass pea seed) and cycad seeds. A method was developed for quantitative determination of the non-protein amino acid, dencichine, in plant samples of P. notoginseng and the adventitious roots directly from the explants of P. notoginseng after derivatization with ethyl chloroformate (ECF) by gas chromatography-mass spectrometry (GC-MS). l-2-chlorophenylalanine was used as an internal standard. Calibration curves were linear (r(2)=0.9988, n=6) in the range of 10-800 microg/ml for dencichine. Limit of detection and quantification for dencichine were 0.5 microg/ml and 2 microg/ml, respectively. This rapid and specific method may be applied to the quantification of dencichine in complex medicinal plants and their products.

Analysis of 25 underivatized amino acids in human plasma using ion-pairing reversed-phase liquid chromatography/time-of-flight mass spectrometry

Amino acids in biological fluids have previously been shown to be detectable using liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS) with perfluorinated acids as ion-pairing agents. To date, these studies have used precursor mass, retention time and tandem mass spectrometry (MS/MS) to identify and quantify amino acids. While this is a potentially powerful technique, we sought to adapt the method to time-of-flight (TOF)MS. A new application of a recently described liquid chromatographic separation method was coupled with TOFMS to employ accurate mass for qualitative identification; resulting in additional qualitative data not available with standard single quadrupole data. In the current study, we evaluated 25 physiological amino acids and one dipeptide that are routinely quantified in human plasma. Accuracy and precision of the method was evaluated by spiking human plasma with a mix of the 25 amino acids; in addition, the inclusion of a cation-exchange cleanup step was evaluated. The calibration curves were linear over a range from 1.56 to 400 microM. The dynamic range was found to be within physiological levels for all amino acids analyzed. Accuracy and precision for most of the amino acids was between 80-120% spike recovery and <10% relative standard deviation (RSD). The LC/MS technique described in this study relies on mass accuracy and is suitable for the quantitation of free amino acids in plasma.

A simple and selective method for the measurement of leucine and isoleucine from plasma using electrospray ionization tandem mass spectrometry

An analytical method was developed for the rapid and accurate quantification of leucine (LEU) and isoleucine (ILE) from plasma using electrospray ionization tandem mass spectrometry (ESI-MS/MS). The two isomeric amino acids were selectively detected using fragment ions unique to each compound. As a result, the need for chromatographic separation was avoided allowing for faster analysis (3 min). The possibility of any considerable interference between the two transitions was closely monitored, with no significant interference being observed. The presence of interfering compounds in plasma was also evaluated and found to minimal. The method was evaluated based upon linearity, with r2>or=0.995 for both compounds, and accuracy, with no more than 8% deviation from the theoretical value.

Application of ethyl chloroformate derivatization for gas chromatography-mass spectrometry based metabonomic profiling

A new combined gas chromatography and mass spectrometry (GC-MS) method has been developed suitable for the urine sample treatment in aqueous phase with ethyl chloroformate (ECF) derivatization agents. The method has been extensively optimized and validated over a broad range of different compounds and urine samples. Analysis of test metabolite derivatives, containing spiked standards, or rat urine exhibited acceptable linearity, satisfactory intra-batch precision (repeatability) and stability, relative standard deviations (R.S.D.) less than 10 and 15% within 48 h, respectively. The quantification limits were 150-300 pg on column for most metabolites. Recovery of several representative compounds, at different concentrations, ranged from 70 to 120%, with R.S.D. better than 10% for rat urine. We were able to generally eliminate potentially confounding variables such as medium complexity, different urea concentrations, and/or derivatization procedure variability. Metabonomic profiling of 1,2-dimethylhydrazine (DMH)-induced precancerous colon rat urine using GC-MS with ECF derivatization was performed to evaluate the proposed method. The analytical variation of the method was smaller than the biological variation in the rat urine samples, proving the suitability of the method to analyze differences in the metabonome of a living system with perturbed metabolic network. Thus, the proposed GC-MS analytical method is reliable to analyze a large variety of metabolites and can be used to investigate human pathology including disease onset, progression, and mortality.

Gas chromatographic determination of amino acids via one-step phase-transfer catalytic pentafluorobenzylation–preconcentration

The gas chromatographic determination of amino acids via their simultaneous extraction, preconcentration and pentafluorobenzylation is reported. Using phase-transfer catalysis (PTC), the amino acids under study were transformed to their pentafluorobenzyl adducts. The method was tested for different catalysts and tetrabutylammonium bromide provided favorable features in comparison to the other PTCs. The derivatization procedure was optimized and the best reaction conditions are given. With the exception of arginine, 19 amino acids were converted to volatile derivatives and analyzed with GC/MS and GC/FID at low concentration levels with acceptable sensitivity and good reproducibility. The LODs were found to range from 0.7 to 2.3microM for the GC/MS analyses and from 1.7 to 6.9microM for GC/FID analyses. The method practicability and applicability were confirmed by the analysis of urine, fruit juice and wheat flour for the determination of the amino acids under study. Protein-bound amino acids were analyzed after an alkaline hydrolysis step with 5M NaOH applying this method to wheat flour with an overall procedure duration less than 12h. The optimized protocol was applied to these samples without any pretreatment and their amino acid concentrations were calculated from the appropriate calibration plots.

Simultaneous Determination of Essential Basic Amino Acids in Pharmaceuticals by Capillary Isotachophoresis

Capillary isotachophoresis (ITP) in cationic regime of the separation with conductometric detection has been used for the separation and determination of basic amino acids (arginine, histidine, and lysine) in pharmaceutical preparations. Several electrolyte systems of different compositions and pH were examined. The optimized ITP electrolyte system consisted of 10 mmol/L potassium acetate adjusted to pH 4.0 with acetic acid as the leading electrolyte with the electroosmotic-flow (EOF) suppressing additive, 0.2% (w/v) methylhydroxyethylcellulose (m-HEC), and 10 mmol/L beta-alanine as the terminating electrolyte. The proposed electrophoretic method was successfully validated. It was convenient for the sensitive, simple, rapid and highly reproducible assay of these amino acids. Good quantitation was obtained in short analysis times (a single analysis took about 10 min). The minimal sample pretreatment and low running costs make the proposed ITP method a good alternative to commonly used analytical methods. The obtained results suggest that the proposed method is suitable for routine assay of basic amino acids in pharmaceuticals.

Amino acid analysis by using comprehensive two-dimensional gas chromatography

The separation characteristics of alkylchloroformate-derivatised amino acids (AAs) by using comprehensive two-dimensional gas chromatography (GCxGC) is reported. The use of a low-polarity/polar column set did not provide as good a separation performance as that achieved with a polar/non-polar column set, where the latter appeared to provide less correlation over the separation space. The degree of component correlation in each column set was estimated by using the correlation coefficient (r(2); for (1)t(R) and (2)t(R) data) with the low-polarity/polar and polar/low-polarity sets returning correlation coefficients of 0.86, and 0.00 respectively, under the respective conditions employed for the experiments. The 1.5-m non-polar (2)D column (0.1-mm ID; 0.1-mum film thickness) gave peak halfwidths of the order of 50-80 ms. Linearity of detection was good, over a three order of magnitude concentration range, with typical lower detection limit of ca. 0.01 mg L(-1), compared with 0.5 mg L(-1) for normal GC operation with splitless injection. The method was demonstrated for analysis of AAs in a range of food and beverage products, including wine, beer and honey. The major AA in these samples was proline. The Heineken beer sample had a relatively more complex and more abundant AA content compared with the other beer sample. The wine and honey samples also gave a range of AA compounds. Repetition of the sample preparation/analysis procedure for the honey sample gave acceptable reproducibility for individual AAs.