Determination Of Sulfur-containing Amino Acids Research Articles

Selective Voltammetric Determination of Sulfur-Containing Amino Acids in Drugs and Vitamin Complexes on an Electrode Modified by a Ruthenium-Hexachloroplatinate Film

An inorganic film of ruthenium hexachloroplatinate (RuPtCl6) deposited on the surface of a glassy-carbon electrode exhibited catalytic activity for oxidation of S-containing amino acids. Catalytic electrochemical oxidation of cysteine, cystine, and methionine occurred at various potentials. The optimum conditions for producing a RuPtCl6 film that gave the greatest catalytic effect were found. A method for selective voltammetric determination of cysteine, methionine, and cystine at an RuPtCl6-film electrode was developed. The lower limit of quantitation of cysteine and cystine was 5 × 10–6 M; of methionine, 5 × 10–7 M. The proposed voltammetric method was used to determine cysteine, cystine, and methionine in drugs and vitamin complexes.

Селективное вольтамперометрическое определение серусодержащих аминокислот в лекарственных средствах и витаминных комплексах на электроде, модифицированном пленкой из гексахлороплатината рутения

Неорганическая пленка из гексахлороплатината рутения (III) (RuPtCl6), осажденная на поверхности электрода из стеклоуглерода, проявляет каталитическую активность при окислении серусодержащих аминокислот. Каталитическое электроокисление цистеина, цистина и метионина происходит при различных потенциалах. Выявлены оптимальные условия получения пленки RuPtCl6, при которых регистрируется наибольший каталитический эффект. Разработан способ селективного вольтамперометрического определения цистеина, метионина и цистина на электроде с пленкой RuPtCl6. Нижняя граница определяемых содержаний цистеина и цистина составляет 5 · 10–6 М, а метионина – 5 · 10–7 М. Предложенный способ вольтамперометрического определения использован для определения цистеина, цистина и метионина в лекарственных средствах и витаминных комплексах.

Electrochemical oxidation of sulfur-containing amino acids on an electrode modified with multi-walled carbon nanotubes

MWNT-modified electrodes are introduced for the voltammetric determination of sulfur-containing amino acids. The morphology of the electrode surface has been characterized by atomic force microscopy. The MWNT layer consists of deeply intertwined vermicular structures with the average diameter of 25 nm. Cysteine, glutathione and methionine are oxidized on the electrode while only cysteine gives signals on the glassy carbon (GC) electrode. The application of such electrodes leads to a decreased overpotential and increase of oxidation currents for cysteine in comparison with a bare GC electrode. The schemes of oxidation are proposed. A decrease of the lower limit of determination and an enlargement of the analytical range for antioxidants were obtained. A simple, fast and accurate procedure for the voltammetric determination of methionine in pharmaceuticals has been developed and can be recommended for quality control purposes.

Electrocatalytic Oxidation and Flow-Injection Determination of Sulfur-Containing Amino Acids at Graphite Electrodes Modified with a Ruthenium Hexacyanoferrate Film

The electrochemical behavior of sulfur-containing amino acids (cysteine, cystine, and methionine) at graphite electrodes modified with a ruthenium(III) hexacyanoferrate(II) film was studied. Glassy carbon and carbon paste were used as graphite materials. The electrocatalytic oxidation of amino acids at a modified electrode resulted in a decrease in the oxidation potentials of amino acids and an increase in the currents of their oxidation peaks as compared to those observed at an unmodified electrode. The voltammetric characteristics and hydrodynamic conditions for detecting the maximum catalytic current were found. A procedure is proposed for the electrocatalytic determination of cysteine, cystine, and methionine at a carbon-paste electrode modified with an inorganic film of ruthenium(III) hexacyanoferrate(II) under the conditions of flow-injection analysis.

Determination of sulfur-containing amino acids by capillary electrophoresis dynamic reaction cell inductively coupled plasma mass spectrometry

Capillary electrophoresis dynamic reaction cell™ inductively coupled plasma mass spectrometry (CE-DRC-ICP-MS) for the determination of sulfur-containing amino acids is described. The sulfur-containing amino acids studied include l-cysteine, l-cystine, dl-homocystine and l-methionine. The species studied were well separated using a 70 cm length×75 μm i.d. fused silica capillary while the applied voltage was set at +22 kV and a 10 mmol l −1 disodium tetraborate buffer (pH 9.8) containing 0.1 mmol l −1 EDTA and 0.5 mmol l −1 Triton X-100 was used as the electrophoretic buffer. The sulfur-selective electropherogram was determined at m/ z 48 as 32 S 16 O + by using its reaction with O 2 in the reaction cell. The method avoided the effect of polyatomic isobaric interferences at m/ z 32 caused by 16 O 16 O + and 14 N 18 O + on 32 S + by detecting 32 S + as the oxide ion 32 S 16 O + at m/ z 48, which is less interfered. The detection limit of various species studied was in the range of 0.047–0.058 μg S ml −1, which corresponded to the absolute detection limit of 1.3–1.6 pg S based on the injection volume of 27 nl. We determined the concentrations of selected sulfur-containing amino acids in urine and nutritive complement samples. The recovery was in the range of 92–128% for various species.

Selective flow-injection biamperometric determination of sulfur-containing amino acids and structurally related compounds

A simple and selective flow-injection method for the determination of cysteine and methionine is proposed. The method is based on the reaction of the amino acid with chloramine-T and the subsequent reaction of the excess of chloramine-T with an acidic solution of iodide producing a stoichiometric amount of tri-iodide (diminution of the flow-injection analysis (FIA) peak) which is determined biamperometrically using two platinum electrodes polarized at 100 mV. The calibration graph is linear up to 10 μg ml −1 of cysteine and 30 μg ml −1 of methionine; the limit of detection is 0.06 and 0.1 μg ml −1; the repeatability (also as percent of a series of 70 continuous FIA peaks of 5 μg ml −1 of cysteine or 15 μg ml −1 of methionine) is 1.1 and 0.7 for cysteine and methionine, respectively. The sample throughput is 220 h −1 in both cases. A large study on the influence of foreign substances is performed especially focused on the rest of l-amino acids. The method is applied to the determination of cysteine, methionine and N-acetyl-cysteine, penicillamine and cystine as structurally related compounds in pharmaceutical and veterinary samples. Finally, the proteins methionine enkephalin and oxytocin are determined on the basis of their contents in both amino acids.

Determining sulfur-containing amino acids by capillary electrophoresis: a fast novel method for total homocyst(e)ine human plasma.

A high-performance capillary electrophoresis (HPCE) method based on laser-induced fluorescence detection is presented here. It enables the determination of sulfur-containing amino acids within 15 min. Fluorescence of sulfur-containing amino acids in plasma is linear over a range of 50-150 micromol/L for L-methionine, 5-100 micromol/L for L-homocysteine, and 50-200 micromol/L for L-cysteine. For homocysteine, we were able to detect 1 fmol injected, equivalent to a plasma concentration of 10 nmol/L. A similar sensitivity is present for cysteine, an even lower one being found for methionine. The intra- and interassay relative standard deviations are < 1%. High-performance liquid chromatography (HPLC) methods are commonly employed for quantifying blood concentrations of sulfur-containing amino acids. A comparative analysis of HPCE and HPLC quantitation of homocysteine has been carried out in 61 blood samples. Plasma concentrations measured by HPCE were in good agreement with those obtained employing an HPLC-based method, a satisfactory correlation being observed between the concentrations obtained by the two methods (r= 0.9972). Thus, the HPCE-based procedure presented here for the measurement of sulfur-containing amino acids in plasma is a simple, fast, accurate, and very sensitive method, suitable for routine determinations in clinical studies.

Determining sulfur-containing amino acids by capillary electrophoresis: A fast novel method for total homocyst(e)ine human plasma

A high-performance capillary electrophoresis (HPCE) method based on laser-induced fluorescence detection is presented here. It enables the determination of sulfur-containing amino acids within 15 min. Fluorescence of sulfur-containing amino acids in plasma is linear over a range of 50—150 μmol/L for L-methionine, 5—100 μmol/L for L-homocysteine, and 50—200 μmol/L for L-cysteine. For homocysteine, we were able to detect 1 fmol injected, equivalent to a plasma concentration of 10 nmol/L. A similar sensitivity is present for cysteine, an even lower one being found for methionine. The intra- and interassay relative standard deviations are < 1%. High-performance liquid chromatography (HPLC) methods are commonly employed for quantifying blood concentrations of sulfur-containing amino acids. A comparative analysis of HPCE and HPLC quantitation of homocysteine has been carried out in 61 blood samples. Plasma concentrations measured by HPCE were in good agreement with those obtained employing an HPLC-based method, a satisfactory correlation being observed between the concentrations obtained by the two methods (r = 0.9972). Thus, the HPCE-based procedure presented here for the measurement of sulfur-containing amino acids in plasma is a simple, fast, accurate, and very sensitive method, suitable for routine determinations in clinical studies.

Simultaneous determination of urinary cystathionine, lanthionine, [formula omitted] and their cyclic compounds using liquid chromatography-mass spectrometry with atmospheric pressure chemical ionization

A measurement system for cystathionine (Cysta) lanthionine (LT), and S-(2- aminoethyl)- l - cysteine (AEC), and reduced products of their ketimines, perhydro-1,4-thiazapine-3,5-dicarboxylic acid (PHTZDC), 1,4-thiomorpholine-3,5-dicarboxylic acid (TMDA) and 1,4-thiomorpholine-3-carboxylic acid (TMA) in the urine samples of a patient with cystathioninuria and normal human subjects has been developed, using column liquid chromatography-mass spectrometry. The recoveries were about 90–105% for Cysta, LT and AEC, and about 77–87% for PHTZDC, TMDA and TMA after ion-exchange treatment. The concentrations of Cysta and PHTZDC in the urine of a patient with cystathioninuria were much higher compared with those in the urine of normal human subjects. The concentrations of AEC and TMDA were almost the same. LT and TMA could not be detected in the urine samples by this method. This method proved useful for the determination of sulfur-containing amino acids and their cyclic compounds in biological samples.

Amino Acid Analysis of Feeds in The Netherlands: Four-Year Proficiency Study

To improve accuracy and precision of amino acid analysis in 12 Dutch feed laboratories, a proficiency study was organized twice annually over a 4-year period. The method used included reflux acid hydrolysis for 22 h followed by evaporation, separation on a cation-exchange resin in an amino acid analyzer, and photometric detection after post-column derivatization with ninhydrin. For the determination of sulfur-containing amino acids, samples were oxidized prior to hydrolysis. For the determination of tryptophan, samples underwent an alkaline hydrolysis excluding oxygen, were separated by liquid chromatography on a Hypersil ODS analytical column, and were assayed by UV or fluorescence detection. The average relative standard deviations within (CVr) and between (CVR) laboratories were 3 and 7%, respectively. For some mixed feed samples, the results from the proficiency study were compared with those obtained by the International Analytical Group. For those samples, the relative standard deviation of the difference between IAG and Dutch groups was only 1.9%. For samples that were analyzed twice during this 4-year period, relative standard deviation of between-series differences was only 2.1%.