Enantiomeric separation of amino acids derivatized with 7-fluoro-4-nitrobenzoxadiazole by capillary liquid chromatography/tandem mass spectrometry

Enantiomeric separation of free L- and D-amino acids in hydrolyzed protein fertilizers by capillary electrophoresis tandem mass spectrometry

Two capillary electrophoresis-tandem mass spectrometry (CE-MS(2)) methods were optimized in this work using cyclodextrins (CDs) as chiral selectors in order to determine the degree of racemization of the free amino acids contained in different hydrolyzed protein fertilizers used as plant biostimulants. The methodologies developed were characterized by the specificity of MS(2) experiments enabling the identification of all protein amino acids, except for cysteine. The enantiomeric separation of up to 14 amino acids was achieved with resolutions above 1.0 and limits of detection between 0.02 and 0.8 μM. The methods were applied to the analysis of complex samples such as hydrolyzed protein fertilizers to evaluate the presence of d-amino acids after different kinds of hydrolysis treatments. The results corroborated the absence or almost negligible presence of enantiomeric conversions of the L-amino acids into D-amino acids in the case of fertilizers obtained by enzymatic hydrolysis, as well as the high racemization rate for those obtained through a chemical hydrolysis.

A sensitive fluorescence reagent, 2-[2-(7H-dibenzo[a,g]carbazol-7-yl)-ethoxy]ethyl chloroformate, for amino acids determination in Saussurea involucrate and Artemisia capillaris Thunb using high-performance liquid chromatography with fluorescence detection and identification with mass spectroscopy/electrospray ionization source

Recent researches shows that amino acids (AA) are not only cell signaling molecules but are also regulators of gene expression and the protein phosphorylation cascade. More precise analysis of AA composition is reckoned to be one of the most important applications in the biomedical and pharmaceutical fields. In this paper, we develop a sample, sensitive and mild method using 2-[2-(7H-dibenzo[a,g]carbazol-7-yl)-ethoxy]ethyl chloroformate (DBCEC) as A labeling reagent for AA determination by high-performance liquid chromatography (HPLC) with fluorescence detection (FLD) and identification with mass spectroscopy. The maximum excitation and emission wavelengths for DBCEC-AA derivatives were 300 and 395 nm, respectively. This method, in conjunction with a gradient elution, offered a baseline resolution of 20 AA on a reversed-phase Hypersil BDS C(18) column. LC separation for the derivatized AA showed good reproducibility, and all AA were found to give excellent linear responses with correlation coefficients > 0.9993. The calculated detection limits with a 25.0 fmol injection of each AA (at a signal-to-noise ratio of 3:1) ranged from 2.62 to 22.6 fmol. This method was applied to determine the AA composition in Saussurea involucrate and Artemisia capillaris Thunb. Meanwhile, this method exhibits a powerful potential for trace analysis of AA from biomedicine, foodstuff and other complex samples.

Review of recent advances in analytical techniques for the determination of neurotransmitters

Methods and advances for monitoring neurotransmitters in vivo or for tissue analysis of neurotransmitters over the last five years are reviewed. The review is organized primarily by neurotransmitter type. Transmitter and related compounds may be monitored by either in vivo sampling coupled to analytical methods or implanted sensors. Sampling is primarily performed using microdialysis, but low-flow push-pull perfusion may offer advantages of spatial resolution while minimizing the tissue disruption associated with higher flow rates. Analytical techniques coupled to these sampling methods include liquid chromatography, capillary electrophoresis, enzyme assays, sensors, and mass spectrometry. Methods for the detection of amino acid, monoamine, neuropeptide, acetylcholine, nucleoside, and soluble gas neurotransmitters have been developed and improved upon. Advances in the speed and sensitivity of these methods have enabled improvements in temporal resolution and increased the number of compounds detectable. Similar advances have enabled improved detection at tissue samples, with a substantial emphasis on single cell and other small samples. Sensors provide excellent temporal and spatial resolution for in vivo monitoring. Advances in application to catecholamines, indoleamines, and amino acids have been prominent. Improvements in stability, sensitivity, and selectivity of the sensors have been of paramount interest.

D-Amino acids in rat brain measured by liquid chromatography/tandem mass spectrometry

Previous work has established that D-amino acids including D-serine (D-Ser) and D-aspartic acid (D-Asp) fulfill specific biological functions in the brain. In this work, the levels and anatomical distribution of d-amino acids in rat brain were determined by using an advantageous liquid chromatography/tandem mass spectrometric analytical method. The study was focused on D-Ser, D-Asp, and D-glutamic acid (D-Glu) because of the significance of L-Asp, L-Glu, and D-Ser in the nervous system. Prenatal, postnatal pups, and 90-day old rats were studied. Results indicated that D-Asp and D-Ser occurred in rat brain at the microg/g tissue level. However, D-Glu was not detected (< 110 ng/g tissue). Throughout the developmental stages d-Asp content in rat brain decreased rapidly from 9.42% of total Asp in 5-day prenatal rats to an undetectable level (< 150 ng/g tissue) in 90-day old rats. In contrast, D-Ser level increased gradually throughout the developmental stages. D-Ser percentage (D-Ser/(D-Ser + L-Ser)) changed from 4.94% in 5-day prenatal rats to 13.7% in 90-day old rats. Regional levels of D-Ser were found to be significantly higher in cortex, striatum, and hippocampus than in thalamus. D-Ser was not detected in cerebellum (< 172ng/g tissue).

Development and validation of a liquid chromatographic method for the determination of branched-chain amino acids in new dosage forms

A reversed-phase liquid chromatographic method (RP-LC) is proposed and validated for the analysis of branched-chain amino acids (l-leucine, l-isoleucine and l-valine) in new pharmaceutical formulations. The pre-column derivatization reaction of these amino acids with 2,4-dinitrofluorobenzene (DNFB) has been investigated considering the matrix effect. The compound reacts at 60 degrees C for 10 min at pH 9 with the amino function, in presence of cetyltrimethylammonium bromide (CTAB), to give adducts that have been separated on a RP amide C16 column and detected at lambda=360 nm. Linear responses were observed for each derivative. The intra-day precision (R.S.D.) was <or=2.22% and there was no significant difference between intra- and inter-day data. Recovery studies showed good results for all amino acids (98.9-100.9%) with R.S.D. ranging from 0.1% to 0.8%. The limit of quantitation was about 20 nmol/mL.

Capillary high-performance liquid chromatography with mass spectrometry for simultaneous determination of major flavonoids, iridoid glucosides and saponins in Flos Lonicerae

Flos Lonicerae, a traditional herbal medicine, has been used in China to treat some inflammatory disease. Several different classes of compounds have been separated from the herb to assess their pharmacological activities. Among these classes, flavonoids, iridoid glycosides and saponins have been well studied and may be responsible for its clinical application. Therefore, quality control of Flos Lonicerae is an important issue for drug safety and validity evaluations. A quantitative method consisting of solid phase extraction followed by capillary high-performance liquid chromatography-diode array detection/electrospray ionization mass spectrometry (capillary HPLC-DAD/ESI-MS) was developed for simultaneously assay of 24 compounds in Flos Lonicerae. Under optimized capillary HPLC-DAD/ESI-MS conditions, these compounds, including nine flavonoids, eight iridoid glucosides and seven saponins, were separated with high efficiency in the selected-ion monitoring (SIM) mode. Linearity of the method was good with correlation coefficients (r(2)) in the range of 0.9935-0.9998 and detection limits were lower than 2.57 ng/mL for most of analytes. The obtained recoveries varied between 91.0 and 108.7% with the relative standard deviations (RSDs) within 8.74% (n=3). The capillary HPLC-DAD/ESI-MS method was also successfully applied to the analysis of these compounds in five species of Flos Lonicerae. It was demonstrated to be a powerful tool for comprehensive analysis of herbal medicines, owing to its exclusive selectivity and excellent sensitivity.

Comprehensive analysis of branched aliphatic d-amino acids in mammals using an integrated multi-loop two-dimensional column-switching high-performance liquid chromatographic system combining reversed-phase and enantioselective columns

A validated two-dimensional HPLC method for the comprehensive analysis of small quantities of branched aliphatic D-amino acids in the presence of large amounts of their L-congeners in mammalian tissues and physiological fluids is described. The quantitative analysis of these aliphatic amino acids (Val, allo-Ile, Ile, and Leu) is important for the diagnosis of various inherent metabolic disorders of amino acids, and the D-enantiomers are expected to be of particular interest from a pharmacological point of view. Target analytes were determined as their fluorescent derivatives, pre-column labeled with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F), using an automated two-dimensional column-switching high-performance liquid chromatographic system combining a narrow bore reversed-phase column and an enantioselective column connected with an integrated multi-loop peak fraction storage device. The described two-dimensional analysis concept proved to be successful for the given task in biological samples taken from mammals. Total analysis time for the reversed-phase separation of the four target NBD-amino acids is 60 min, and the integrated enantiomer separation of each of the four analytes is completed in approximately 5 min. In the rat, significant amounts of D-Leu were found in all tissues and physiological fluids tested (trace-1.3 nmol/g tissue), and in the urine, the presence of high amounts of D-allo-Ile (D-isomer of a non-proteinogenic amino acid, 22.2 nmol/ml) was demonstrated. D-allo-Ile was also found in the urine of dog and mouse, which indicates the ubiquitous presence of this unusual D-amino acid and the potential need to clarify its unique metabolism in mammals.

Study of a new derivatizing reagent that improves the analysis of amino acids by HPLC with fluorescence detection: application to hydrolyzed rape bee pollen

A simple and sensitive method for evaluating the chemical compositions of protein amino acids, including cystine (Cys)(2) and tryptophane (Try) has been developed, based on the use of a sensitive labeling reagent 2-(11H-benzo[alpha]-carbazol-11-yl) ethyl chloroformate (BCEC-Cl) along with fluorescence detection. The chromophore of the 1,2-benzo-3,4-dihydrocarbazole-ethyl chloroformate (BCEOC-Cl) molecule was replaced with the 2-(11H-benzo[alpha]-carbazol-11-yl) ethyl functional group, yielding the sensitive fluorescence molecule BCEC-Cl. The new reagent BCEC-Cl could then be substituted for labeling reagents commonly used in amino acid derivatization. The BCEC-amino acid derivatives exhibited very high detection sensitivities, particularly in the cases of (Cys)(2) and Try, which cannot be determined using traditional labeling reagents such as 9-fluorenyl methylchloroformate (FMOC-Cl) and ortho-phthaldialdehyde (OPA). The fluorescence detection intensities for the BCEC derivatives were compared to those obtained when using FMOC-Cl and BCEOC-Cl as labeling reagents. The ratios I (BCEC)/I (BCEOC) = 1.17-3.57, I (BCEC)/I (FMOC) = 1.13-8.21, and UV(BCEC)/UV(BCEOC) = 1.67-4.90 (where I is the fluorescence intensity and UV is the ultraviolet absorbance). Derivative separation was optimized on a Hypersil BDS C(18) column. The detection limits calculated from 1.0 pmol injections, at a signal-to-noise ratio of 3, ranged from 7.2 fmol for Try to 8.4 fmol for (Cys)(2). Excellent linear responses were observed, with coefficients of >0.9994. When coupled with high-performance liquid chromatography, the method established here allowed the development of a highly sensitive and specific method for the quantitative analysis of trace levels of amino acids including (Cys)(2) and Try from bee-collected pollen (bee pollen) samples.

Quantification of D-amino acids in the central nervous system of Aplysia californica by liquid chromatography/tandem mass spectrometry

A sensitive, specific and reliable liquid chromatography/tandem mass spectrometry (LC/MS/MS) method has been developed for simultaneous determination of D-amino acids in the central nervous system (CNS) of Aplysia californica. In order to correct for any potential matrix effects on measured signals, deuterium-labeled L-Asp-d3 was used as an internal standard. Pre-column derivatization of the sample with 7-fluoro-4-nitrobenzoxadiazole (NBD-F) allowed both effective in-line pre-concentration and sensitive MS/MS detection of the analytes. An extraction column (50x0.25 mm, 5 microm C18 silica particles) was used to pre-concentrate/stack samples. Enantiomeric separation of amino acid enantiomers was achieved on a chiral column packed with teicoplanin aglycone bonded silica particles (170x0.25 mm, 5 microm) with an MS-friendly mobile phase. The characteristic precursor to product ion transitions, m/z 297-->279 (for NBD-Asp), m/z 269-->223 (For NBD-Ser), m/z 311-->293 (for NBD-Glu) and m/z 300-->282 (for NBD-L-Asp-d3) were monitored for the quantification. Samples from the CNS of A. californica and heart tissues were analyzed. D-Asp was detected at high levels in all the ganglia and nerve tissues, but not in the heart tissue. Further, neither D-Ser nor D-Glu was detected in Aplysia, a widely used neuronal model.

Assay of Trace d-Amino Acids in Neural Tissue Samples by Capillary Liquid Chromatography/Tandem Mass Spectrometry

A sensitive chiral capillary HPLC-MS/MS method well suited for the determination of amino acid enantiomers in biological samples was developed. The method involved precolumn derivatization of the sample with 7-fluoro-4-nitrobenzoxadiazole (NBD-F). After derivatization, NBD-amino acids were stacked on a C18 reversed-phase extraction microcolumn, thus enriching and cleaning up the analytes. Various chiral stationary phases (CSPs) including cyclodextrin-bonded silica, Pirkle-type, vancomycin, and teicoplanin-bonded silica particles were evaluated for resolving NBD-F tagged amino acid enantiomers with mobile phases compatible with MS detection. It was found that only teicoplanin aglycon CSP provided sufficient resolution of NBD-Asp and NBD-Ser enantiomers to quantify trace levels of D-Asp and D-Ser in tissue samples. MS/MS detection of NBD-amino acid derivatives was very sensitive and selective. The high selectivity allowed the use of a stable isotope-labeled analyte analogue (i.e., L-aspartic acid-2,3,3-d3) as internal standard for the quantitation to improve assay reproducibility and reliability. Neural tissue samples dissected from rat brain and the central nervous system (CNS) of Aplysia californica, a widely used neuronal model, were analyzed to determine the chirality of glutamic acid (Glu), aspartic acid (Asp), and serine (Ser). The former two are major excitatory amino acids in the brain, and the last one has been recently identified as a neuromodulator. Both D-Ser and D-Asp were detected in rat brain. While the D-Asp level decreased rapidly through the developmental stages of the rat, the D-Ser level increased steadily from 82.3 microg/g of wet tissue in 3-day prenatal rats to 241.3 microg/g of wet tissue in 90-day-old rats. Interestingly, no D-Ser was detected in the CNS of Aplysia, a "primitive" invertebrate. However, the D-Asp level in this animal was found to be high. In a particular connective nerve sample, D-Asp was at 323.2 microg/g of wet tissue and constituted 60.2% of total Asp. D-Glu was not detected either in rat brain or in Aplysia's CNS.

Derivatization in mass spectrometry--8. Soft ionization mass spectrometry of small molecules

This is the first of two reviews devoted to derivatization approaches for "soft" ionization mass spectrometry (FAB, MALDI, ESI, APCI) and deals, in particular, with small molecules. The principles of the main "soft" ionization mass spectrometric methods as well as the reasons for derivatizing small molecules are briefly described. Derivatization methods for modification of amines, carboxylic acids, amino acids, alcohols, carbonyl compounds, monosaccharides, thiols, unsaturated and aromatic compounds etc. to improve their ionizability and to enhance structure information content are discussed. The use of "fixed"-charge bearing derivatization reagents is especially emphasized. Chemical aspects of derivatization and "soft" ionization mass spectrometric properties of derivatives are considered.