Comparison of different chloroformates for the derivatisation of seleno amino acids for gas chromatographic analysis

An easy and sensitive assay for acetohydroxyacid synthases based on the simultaneous detection of substrates and products in a single step

Acetohydroxyacid synthase (AHAS, EC 2.2.1.6) catalyzes the first step in the synthesis of the branched-chain amino acids valine, leucine, and isoleucine, pathways being present in plants and microorganisms, but not in animals. Thus, AHAS is an important target for numerous herbicides and, more recently, for the development of antimicrobial agents. The need to develop new and optimized herbicides and pharmaceuticals requires a detailed understanding of the biochemistry of AHAS. AHAS transfers an activated two-carbon moiety derived from pyruvate to either pyruvate or 2-oxobutyrate as acceptor substrates, forming 2-acetolactate or 2-acetohydroxy-2-butyrate, respectively. Various methods have been described in the literature to biochemically characterize AHAS with respect to substrate preferences, substrate specificity, or kinetic parameters. However, the simultaneous detection and quantification of substrates and unstable products of the AHAS-catalyzed reaction have always been a challenge. Using AHAS isoform II from Escherichia coli, we have developed a sensitive assay for AHAS-catalyzed reactions that uses derivatization with ethyl chloroformate to stabilize and volatilize all reactants in the aqueous solution and detect them by gas chromatography coupled to flame ionization detection or mass spectrometry. This assay allows us to characterize the product formation in reactions in single and dual substrate reactions and the substrate specificity of AHAS, and to reinterpret previous biochemical observations. This assay is not limited to the AHAS-catalyzed reactions, but should be applicable to studies of many metabolic pathways.

Differentiation between Ripening Stages of Iberian Dry-Cured Ham According to the Free Amino Acids Content

In this paper, the differentiation of three ripening stages, postsalting, drying, and cellar, of Iberian dry-cured ham has been carried out according to their free amino acids contents. Eighteen L-amino acids, alanine, 2-aminobutanoic acid, aspartic acid, cysteine, glutamine, glycine, histidine, hydroxyproline, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tyrosine, and valine have been determined by gas chromatography with derivatization with N,O-bis(trimethylsilyl)-trifluoroacetamide. Gas chromatography-mass spectrometry was used to confirm the presence of the eighteen amino acids in the ham samples, and gas chromatography using a DB-17HT column and flame ionization detector was used for quantitative determination. Extraction with a mixture methanol-acetonitrile has been carried out, achieving recoveries in the range 52-164%. Methimazole was used as internal standard. Limits of detection ranged between 7.0 and 611.7 mg·kg-1. Free amino acids have been used as chemical descriptors to differentiate between the ripening stages. Principal component analysis and linear discriminant analysis have been used as chemometric techniques, achieving complete differentiation between the ripening stages. Alanine, tyrosine, glutamine, proline, 2-aminobutanoic acid, cysteine, and valine were the most differentiating amino acids.

Applying gas chromatography to monitor extracellular free amino acids content in cultivation medium during lactic acid fermentation

The aim of this work was the adaptation of a Gas Chromatographic-Flame Ionization Detector (GC-FID) method for detection and quantification of extracellular free amino acids in demineralized water, De Mann Rogosa Sharpe (MRS) medium and corn grits (CG) withdrawn during lactic acid fermentation. In order to analyze free amino acids by the GC-FID method it was necessary to convert free amino acids to volatile compounds. This was accomplished by derivatization of free amino acids with ethylchlor formate in aqueous medium followed by extraction of volatile free amino acid esters with chloroform. It was proven that the combination of derivatization and extraction procedure with developed GC-FID method gave accurate, reproducible and sensitive analytical results. Quantification of 15 (Ala, Gly, Val, Leu, Ile, Phe, Tyr, Trp, Asn, Met, Pro, Lys, His, Asp and Glu) out of 20 ethoxycarbonyl-ethyl esters of free amino acids in demineralized water and MRS medium was achieved by established methods. In corn grits medium all of the above mentioned 15 amino acids, except His, were quantified with this GC-FID method. The established method was efficiently verified in monitoring of extracellular free amino acid concentration during lactic acid production with Lactobacillus rhamnosus DSM 20021T in MRS medium and Lactobacillus amylovorus DSM 20531T in corn grits medium.

Transformation of microcystins to 2-methyl-3-methoxy-4-phenylbutyric acid by room temperature ozone oxidation for rapid quantification of total microcystins

Microcystins (MCs) are cyanobacterial hepatotoxins capable of accumulation into animal tissues. To determine the total microcystins in water, a novel analytical method, including ozonolysis, methylation of 2-methyl-3-methoxy-4-phenylbutyric acid (MMPB) with methylchloroformate (MCF) and gas chromatography mass spectrometry (GC-MS) detection was developed. The results show that MCs can be oxidized by ozone to produce MMPB at ambient temperature, proving ozonation is an effective, rapid and green method for the transformation of MCs to MMPB without secondary pollution. The oxidation conditions as well as the esterification process were optimized and, subsequently applied to analysis of environmental samples. The method shows wide linear range and high sensitivity with a detection limit of 0.34 μg L(-1). The established method was successfully applied to the analysis of microcystins in water samples.

Bringing GC-MS profiling of steroids into clinical applications

Abnormalities of steroid biosynthesis and excretion are responsible for the development and prevention of endocrine disorders, such as metabolic syndromes, cancers, and neurodegenerative diseases. Due to their biochemical roles in endocrine system, qualitative and quantitative analysis of steroid hormones in various biological specimens is needed to elucidate their altered expression. Mass spectrometry (MS)-based steroid profiling can reveal the states of metabolites in biological systems and provide comprehensive insights by allowing comparisons between metabolites present in cells, tissues, or organisms. In addition, the activities of many enzymes related to steroid metabolism often lead to hormonal imbalances that have serious consequences, and which are responsible for the progress of hormone-dependent diseases. In contrast to immunoaffinity-based enzyme assays, MS-based methods are more reproducible in quantification. In particular, high-resolution gas chromatographic (GC) separation of steroids with similar chemical structures can be achieved to provide rapid and reproducible results with excellent purification. GC-MS profiling therefore has been widely used for steroid analysis, and offers the basis for techniques that can be applied to large-scale clinical studies. Recent advances in analytical technologies combined with inter-disciplinary strategies, such as physiology and bioinformatics, will help in understanding the biochemical roles of steroid hormones. Therefore, comprehensive analytical protocols in steroid analysis for different research purposes may contribute to the elucidation of complex metabolic processes relevant to steroid function in many endocrine disorders, and in the identification of diagnostic biomarkers.

A reliable solid phase microextraction-gas chromatography-triple quadrupole mass spectrometry method for the assay of selenomethionine and selenomethylselenocysteine in aqueous extracts: difference between selenized and not-enriched selenium potatoes

A new analytical approach is exploited in the assay of selenium speciation in selenized and not selenium enriched potatoes based on the widely available solid-phase microextraction (SPME) coupled to-GC-triple quadrupole mass spectrometry (SPME-GC-QqQ MS) method. The assay of selenomethionine (SeMet) and selenomethylselenocysteine (SeMeSeCys) in potatoes here reported provides clues to the effectiveness of SPME technique combined with gas chromatography-tandem mass spectrometry, which could be of general use. For the exploitation of the GC method, the selected analytes were converted into their N(O,S)-alkoxycarbonyl alkyl esters derivatives by direct treatment with alkyl chloroformate in aqueous extracts. The performance of five SPME fibers and three chloroformates were tested in univariate mode and the best results were obtained using the divinylbenzene/carboxen/polydimethylsiloxane fiber and propylchloroformate. The variables affecting the efficiency of SPME analysis were optimized by the multivariate approach of design of experiment (DoE) and, in particular, a central composite design (CCD) was applied. Tandem mass spectrometry in selected reaction monitoring (SRM) has allowed the elimination of matrix interferences, providing reconstructed chromatograms with well-resolved peaks and the achievement of very satisfactory detection and quantification limits. Both precision and recovery of the proposed protocol tested at concentration of 8 and 40 μg kg(-1) (dry matter), offered values ranging from 82.3 to 116.3% and from 8.5 to 13.1% for recovery and precision, respectively. The application of the method to commercial samples of selenized and not selenium enriched potatoes proved that the Se fertilization increases significantly the concentration of these bioavailable selenoamino acids.

PHYTOPLANKTON SELENIUM REQUIREMENTS: THE CASE FOR SPECIES ISOLATED FROM TEMPERATE AND POLAR REGIONS OF THE SOUTHERN HEMISPHERE(1)

A series of laboratory culture experiments was used to investigate the effect of selenium (Se, 0-10 nM) on the growth, cellular volume, photophysiology, and pigments of two temperate and four polar oceanic phytoplankton species [coccolithophore Emiliania huxleyi (Lohmann) W. W. Hay et H. P. Mohler, cyanobacterium Synechococcus sp., prymnesiophyte Phaeocystis sp., and three diatoms-Fragilariopsis cylindrus (Grunow) Kriegar, Chaetoceros sp., and Thalassiosira antarctica G. Karst.]. Only Synechoccocus sp. and Phaeocystis sp. did not show any requirement for Se. Under Se-deficient conditions, the growth rate of E. huxleyi was decreased by 1.6-fold, whereas cellular volume was increased by 1.9-fold. Se limitation also decreased chl a (2.5-fold), maximum relative electron transport rate (1.9-fold), and saturating light intensity (2.8-fold), suggesting that Se plays a role in photosynthesis or high-light acclimation. Pigment analysis for Antarctic taxa provided an interesting counterpoint to the physiology of E. huxleyi. For all Se-dependent Antarctic diatoms, Se limitation decreased growth rate and chl a content, whereas cellular volume was not affected. Pigment analysis revealed that other pigments were affected under Se deficiency. Photoprotective pigments increased by 1.4-fold, while diadinoxanthin:diatoxanthin ratios decreased by 1.5- to 4.9-fold under Se limitation, supporting a role for Se in photoprotection. Our results demonstrate an Se growth requirement for polar diatoms and indicate that Se could play a role in the biogeochemical cycles of other nutrients, such as silicic acid in the Southern Ocean. Se measurements made during the austral summer in the Southern Ocean and Se biological requirement were used to discuss possible Se limitation in phytoplankton from contrasting oceanographic regions.

A novel GC-MS method in urinary estrogen analysis from postmenopausal women with osteoporosis

Estrogen metabolites play important roles in the development of female-related disorders and homeostasis of the bone. To improve detectability, a validated gas chromatography-mass spectrometry (GC-MS) method was conducted with two-phase extractive ethoxycarbonlyation (EOC) and subsequent pentafluoropropionyl (PFP) derivatization was introduced. The resulting samples were separated through a high-temperature MXT-1 column within an 8 min run and were detected in the selected ion monitoring (SIM) mode. The optimized analytical conditions led to good separation with a symmetric peak shape for 19 estrogens as their EOC-PFP derivatives. The limit of quantification (LOQ) was from 0.02 to ∼0.1 ng/ml for most estrogens analyzed, except for 2-hydroxyestriol (0.5 ng/ml). The devised method was found to be linear (r² > 0.995) in the range from the LOQ to 40 ng/ml, whereas the precision (% CV) and accuracy (% bias) ranged from 1.4 to 10.5% and from 91.4 to 108.5%, respectively. The good sensitivity and selectivity of this method even allowed quantification of the estrogen metabolites in urine samples obtained from the postmenopausal female patients with osteoporosis. The present technique can be useful for clinical diagnosis as well as to better understand the pathogenesis of estrogen-related disorders in low-level quantification.

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.

Separation and determination of seleno amino acids using gas chromatography hyphenated with inductively coupled plasma mass spectrometry after hollow fiber liquid phase microextraction

A new derivatization-extraction method for preconcentration of seleno amino acids using hollow fiber liquid phase microextraction (HF-LPME) was developed for the separation and determination of seleno amino acids in biological samples by gas chromatography-inductively coupled plasma mass spectrometry (GC-ICP-MS). Derivatization was performed with ethyl chloroformate (ECF) to improve the volatility of seleno amino acids. Parameters influencing microextraction, including extraction solvent, pH of sample solution, extraction time, stirring speed, and inorganic salt concentration have been investigated. Under the optimal conditions, the limits of detection (LODs) obtained for Se-methyl-selenocysteine (SeMeCys), selenomethionine (SeMet), and selenoethionine (SeEth) were 23, 15, and 11 ng Se l(-1), respectively. The relative standard deviations (RSDs) were 14.6%, 16.4%, and 19.4% for SeMeCys, SeMet, and SeEth (c = 1.0 ng ml(-1), n = 7), respectively, and the RSDs for SeMeCys, SeMet could be improved obviously if SeEth was utilized as the internal standard. The proposed method was applied for the determination of seleno amino acids in extracts of garlic, cabbage, and mushroom samples, and the recoveries for the spiked samples were in the range of 96.8-108% and 93.4-115% with and without the use of SeEth as internal standard. The developed method was also applied to the analysis of SeMet in a certified reference material of SELM-1 yeast and the determined value is in good agreement with the certified value.

Production and characterization of fully selenomethionine-labeled Saccharomyces cerevisiae

This paper reports, for the first time, a quantitative replacement of methionine (Met) by selenomethionine (SeMet) at >98% substitution, with up to 4940 microg of SeMet/g of yeast obtained for the entire protein pool of a wild-type yeast grown on a SeMet-containing medium. The incorporation of selenium in yeast proteins, in the form of selenomethionine, and the influence of various organic and inorganic Se and S sources present in the media were monitored during the growth of a wild-type Saccharomyces cerevisiae , which allowed the optimization of the composition of a fully defined synthetic growth medium that ensured maximum SeMet incorporation. Quantitation of SeMet and Met was performed by species-specific isotope dilution GC-MS. The use of ascorbic acid and a minimum concentration of cysteine (5 microg/L) was found to be beneficial to achieve incorporation by limiting the oxidative stress due to the presence of selenium. Except for small amounts of cysteine, no other sources of sulfur were necessary to achieve yeast growth. In a medium containing Se(VI), the maximum replacement of Met with SeMet was 50%, which is considerably higher than that obtained with the current commercial Se yeast formulations. For yeast grown in a Met-free defined medium, which was supplemented with SeMet, nearly total replacement of Met with SeMet could be achieved. The fully Se-labeled yeast could be an important tool for the study of eukaryotic protein structures both by mass spectrometry and by X-ray crystallography through selenomethionine single- and multiple-wavelength anomalous dispersion (SAD and MAD) phasing. In addition, a particular yeast strain, BY4741, that cannot synthesize Met using inorganic sulfur (met15Delta0) was shown to produce SeMet in the presence of inorganic selenium. This might indicate that the incorporation of inorganic selenium salts [Se(VI) and Se(IV)] is obviously not occurring exclusively through the same biological pathways as for sulfur. The reduction of inorganic Se to hydrogen selenide (H(2)Se), its reactions with organic compounds present in the yeast or in the media, and the possible metabolization through unspecific enzymatic pathways (such as transsulfuration) could also be of considerable importance in the production of selenoamino acids during yeast growth.

GC-MS with ethyl chloroformate derivatization for comprehensive analysis of metabolites in serum and its application to human uremia

An optimized method based on GC-MS with ethyl chloroformate derivatization has been developed for the comprehensive analysis of endogenous metabolites in serum. Twenty-two reference standards and serum samples were used to validate the proposed method. The correlation coefficient was higher than 0.9900 for each of the standards, and the LOD varied from 125 to 300 pg on-column. The analytical equipment exhibited good repeatability (RSD<10%) for all of the standards. Both the repeatability and the within-48-h stability of the analytical method were satisfactory (RSD<10%) for the 18 metabolites identified in the serum samples. Mean recovery was acceptable for the 18 metabolites, ranging from 70% to 120% with RSDs of less than 10%. Using the optimized protocol and a subsequent multivariate statistical technique, complete differentiation was achieved between the metabolic profile of uremic patients and that of age- and sex-matched normal subjects. Significantly decreased levels of valine, leucine, and isoleucine and increased levels of myristic acid and linoleic acid were observed in the patient group. This work demonstrated that this method is suitable for serum-based metabolic profiling studies.

Analysis of phenolic acids as chloroformate derivatives using solid phase microextraction–gas chromatography

In the presented study, a simple and original procedure of phenolic acids derivatization treated by ethyl and methyl chloroformate performed in an aqueous media consisting of acetonitrile, water, methanol/ethanol and pyridine has been modified and optimized. Seven phenolic acid standards-caffeic, ferulic, gallic, p-coumaric, protocatechuic, syringic and vanillic were derivatized into corresponding methyl/ethyl esters and subsequently determined by the means of gas chromatography connected to the flame-ionisation detector (FID). Some selected validation parameters as linearity, detection and quantitation limits and peak area repeatability were valued. The total time of gas chromatography (GC) analysis was 24 min for methyl chloroformate and 30 min for ethyl chloroformate derivatization. The more suitable methyl chloroformate derivatization was used for further experiments on the possibility of multiple pre-concentration by the direct solid phase microextraction technique (SPME). For this purpose, polyacrylate (PA), polydimethylsiloxane (PDMS), carboxen/polydimethylsiloxane (CAR/PDMS) and polydimethylsiloxane/divinylbenzene (PDMS/DVB) fibres were tested and the extraction conditions concerning time of extraction, temperature and time of desorption were optimized. The most polar PA fibre gave the best results under optimal extraction conditions (50 min extraction time, 25 degrees C extraction temperature and 10 min desorption time). As a result, the total time of SPME-GC analysis was 74 min and an increase in method sensitivity was reached. The limits of quantitation (LOQ) of p-coumaric, ferulic, syringic and vanillic acid esters after SPME pre-concentration were 0.02, 0.17, 0.2 and 0.2 microg mL(-1), respectively, showing approximately 10 times higher sensitivity in comparison with the original GC method.

Certification of a new selenized yeast reference material (SELM-1) for methionine, selenomethinone and total selenium content and its use in an intercomparison exercise for quantifying these analytes

A new selenized yeast reference material (SELM-1) produced by the Institute for National Measurement Standards, National Research Council of Canada (INMS, NRC) certified for total selenium (2,059+/-64 mg kg(-1)), methionine (Met, 5,758+/-277 mg kg(-1)) and selenomethionine (SeMet, 3,431+/-157 mg kg(-1)) content is described. The +/-value represents an expanded uncertainty with a coverage factor of 2. SeMet and Met amount contents were established following a methanesulfonic acid digestion of the yeast using GC-MS and LC-MS quantitation. Isotope dilution (ID) calibration was used for both compounds, using 13C-labelled SeMet and Met. Total Se was determined after complete microwave acid digestion based on ID ICP-MS using a 82Se spike or ICP-OES spectrometry using external calibration. An international intercomparison exercise was piloted by NRC to assess the state-of-the-art of measurement of selenomethione in SELM-1. Determination of total Se and methionine was also attempted. Seven laboratories submitted results (2 National Metrology Institutes (NMIs) and 5 university/government laboratories). For SeMet, ten independent mean values were generated. Various acid digestion and enzymatic procedures followed by LC ICP-MS, LC AFS or GC-MS quantitation were used. Four values were based on species-specific ID calibration, one on non-species-specific ID with the remainder using standard addition (SA) or external calibration (EC). For total selenium, laboratories employed various acid digestion procedures followed by ICP-MS, AFS or GC-MS quantitation. Four laboratories employed ID calibration, the remaining used SA or EC. A total of seven independent results were submitted. Results for methionine were reported by only three laboratories, all of which used various acid digestion protocols combined with determination by GC-MS and LC UV. The majority of participants submitted values within the certified range for SeMet and total Se, whereas the intercomparison was judged unsuccessful for Met because only two external laboratories provided values, both of which were outside the certified range.

Mass spectrometry in bioinorganic analytical chemistry

A considerable momentum has recently been gained by in vitro and in vivo studies of interactions of trace elements in biomolecules due to advances in inductively coupled plasma mass spectrometry (ICP MS) used as a detector in chromatography and capillary and planar electrophoresis. The multi-isotopic (including non-metals such as S, P, or Se) detection capability, high sensitivity, tolerance to matrix, and large linearity range regardless of the chemical environment of an analyte make ICP MS a valuable complementary technique to electrospray MS and MALDI MS. This review covers different facets of the recent progress in metal speciation in biochemistry, including probing in vitro interactions between metals and biomolecules, detection, determination, and structural characterization of heteroatom-containing molecules in biological tissues, and protein monitoring and quantification via a heteroelement (S, Se, or P) signal. The application areas include environmental chemistry, plant and animal biochemistry, nutrition, and medicine.

Effect of selenium fertilizer on free amino acid composition of broccoli (Brassica oleracea Cv. Majestic) determined by gas chromatography with flame ionization and mass selective detection

Selenium-enriched broccoli florets, harvested from plants grown on soil fertilized with four levels of sodium selenate, were evaluated for their free amino acid composition using alkylchlorformate derivatization, solid-phase extraction, and GC-FID or GC-MS. The selenium-enriched florets contained 0.4 (control), 5.7 (treatment A), 98.6 (treatment B), and 879.2 (treatment C) microg/g Se (dry weight). Twenty-one free amino acids were identified in the control and all three treatments. The total free amino acid content of the broccoli florets ranged from 178 mmol/kg (dry weight), for the control, to 479 mmol/kg (dry weight), for treatment C. Broccoli from treatment C contained the highest level of Se, had the most total free amino acids, and had an extremely high level of glutamine (Gln) when compared to the control and the other two treatments. In general, the smallest addition of Se to the soil (treatment A) induced increased levels of all detectable amino acids when compared to the control, whereas increased additions of Se (treatments B and C) produced mixed responses. Florets from treatment A contained the highest essential amino acid content.

Advances in analytical methodology for bioinorganic speciation analysis: metallomics, metalloproteomics and heteroatom-tagged proteomics and metabolomics

The recent developments in analytical techniques capable of providing information on the identity and quantity of heteroatom-containing biomolecules are critically discussed. Particular attention is paid to the emerging areas of bioinorganic analysis including: (i) a comprehensive analysis of the entirety of metal and metalloid species within a cell or tissue type (metallomics), (ii) the study of the part of the metallome involving the protein ligands (metalloproteomics), and (iii) the use of a heteroelement, naturally present in a protein or introduced in a tag added by means of derivatisation, for the spotting and quantification of proteins (heteroatom-tagged proteomics). Inductively coupled plasma mass spectrometry (ICP MS), used as detector in chromatography and electrophoresis, and supported by electrospray and MALDI MS, appears as the linchpin analytical technique for these emerging areas. This review focuses on the recent advances in ICP MS in biological speciation analysis including sensitive detection of non-metals, especially of sulfur and phosphorus, couplings to capillary and nanoflow HPLC and capillary electrophoresis, laser ablation ICP MS detection of proteins in gel electrophoresis, and isotope dilution quantification of biomolecules. The paper can be considered as a followup of a previous review by the author on a similar topic (J. Szpunar, Analyst, 2000, 125, 963).

Review: derivatization in mass spectrometry-6. Formation of mixed derivatives of polyfunctional compounds

The review describes chemical transformations of multifunctional compounds (amino acids and peptides, amino alcohols, amino thiols, hydroxy acids, oxo acids, oxo alcohols, compounds containing simultaneously three or more different groups etc.) by using step-wise or one-step modification or protection of functional groups. Some chemical aspects of mixed derivatization performed for improving the physical-chemical properties and mass spectral characteristics are discussed. Application of mixed derivatization to qualitative and quantitative analysis of various multifunctional compounds mainly in biological fluids and other matrices by gas chromatography/mass spectrometry in electron ionization, chemical ionization, negative-ion chemical ionization and selected ion monitoring modes is considered.

Comparison of extraction methods for quantitation of methionine and selenomethionine in yeast by species specific isotope dilution gas chromatography–mass spectrometry

Fourteen extraction methods commonly cited in the literature were evaluated for the quantitation of methionine (Met) and selenomethionine (SeMet) in a yeast candidate certified reference material (CRM). Species specific isotope dilution (ID) gas chromatography-mass spectrometry (GC-MS) was utilized to effectively compensate for potential errors, such as losses during derivatization and clean up steps. Despite different extraction methods, the same derivatization procedure using methyl chloroformate was applied with a single exception, which was based on digestion with cyanogen bromide with 2% SnCl2 in 0.1 M HCl. Significant differences in measured Met and SeMet concentrations were obtained when different extraction methods were used. A 4 M methanesulfonic acid reflux digestion was found to be the most efficient for both analytes. Digestion with CNBr with 2% SnCl2 in 0.1 M HCl for the determination of SeMet showed the second highest extraction efficiency. Despite frequent use of enzymatic hydrolysis for the extraction of SeMet from yeast, very low extraction efficiencies for both analytes were obtained for four of eight tested methods. Among these, the highest extraction efficiencies for both analytes were obtained using 20mg pronase and 10mg lipase with incubation at 37 degrees C for 24 h. However, recoveries remained nearly 30 and 50% lower for Met and SeMet, respectively, compared to extraction with methanesulfonic acid. Lowest extraction efficiencies for both analytes were obtained when HCl or tetramethylammonium hydroxide (TMAH) digestions were used. Efficient extraction was also achieved using 200 mg (or 400 mg) of protease XIV with incubation at 37 degrees C for 72 h (or 24 h). Concentrations of 3331+/-45 and 3334+/-39 microg g(-1) (mean and one standard deviation, n = 4) for SeMet were obtained using 200 mg (72 h incubation) and 400 mg (24 h incubation) of protease XIV, respectively, in agreement with a value of 3404+/-38 microg g(-1) obtained using a methanesulfonic acid reflux.

Rapid and sensitive method for determining free amino acids in honey by gas chromatography with flame ionization or mass spectrometric detection

This paper describes a rapid, sensitive and specific method for determination of free amino acids in honey involving a new reaction of derivatization and gas chromatography (GC) with flame ionization (FID) and mass spectrometric (MS) detection. The method allows the determination of 22 free amino acids in honey samples in a short time: 8 and 5 min for GC-FID and GC-MS, respectively. Quantitation was performed using Norvaline as internal standard, with detection limits ranging between 0.112 and 1.795 mg/L by GC-FID and between 0.001 and 0.291 mg/L by GC-MS in the selected-ion monitoring mode. The method was validated and applied to a set of 74 honey samples belonging to four different botanical origins: eucaliptus, rosemary, orange and heather. The statistical treatment of data shows a correct classification of different origins over 90%.

Rapid determination of amino acids in neonatal blood samples based on derivatization with isobutyl chloroformate followed by solid-phase microextraction and gas chromatography/mass spectrometry

The purpose of this study was to develop a simple, rapid and sensitive analytical method for determination of amino acids in neonatal blood samples. The developed method involves the employment of derivatization and a solid-phase microextraction (SPME) technique together with gas chromatography/mass spectrometry (GC/MS). Amino acids in blood samples were derivatized by a mixture of isobutyl chloroformate, methanol and pyridine, and the N(O,S)-alkoxycarbonyl alkyl esters thus formed were headspace extracted by a SPME fiber. Finally, the extracted analytes on the fiber were desorbed and detected by GC/MS in electron impact (EI) mode. L-Valine, L-leucine, L-isoleucine, L-phenylanaline and L-tyrosine in blood samples were quantitatively analyzed by measurement of the corresponding N(O,S)-alkoxycarbonyl alkyl esters using an external standard method. SPME conditions were optimized, and the method was validated. The method was applied to diagnosis of neonatal phenylkenuria (PKU) and maple syrup urine disease (MSUD) by the analyses of five amino acids in blood samples. The results showed that the proposed method is a potentially powerful tool for simultaneous screening for neonatal PKU and MSUD.