反相高效液相色谱法测定饲料添加剂阿散酸中的阿散酸及掺假物质对氨基苯磺酸

建立了用于饲料添加剂阿散酸质量控制的反相高效液相色谱法。采用的色谱条件: Waters Bondapak C18柱(150 mm×4 mm, 5 μm)分离,以甲醇-水(用稀磷酸调节pH至2.9) (1:4, v/v)作流动相,流速1.0 mL/min,紫外检测波长为244 nm。在优化的色谱条件下,阿散酸和掺假物质对氨基苯磺酸在3 min内实现了基线分离。阿散酸和对氨基苯磺酸的线性范围均为5～200 mg/L,检出限(S/N=3)分别为0.20 mg/L和0.15 mg/L。该方法简便快速,适合饲料添加剂阿散酸的分析以及监测对氨基苯磺酸掺假。     

甲酸作直接甲醇燃料电池替代燃料

甲酸作直接甲醇燃料电池替代燃料;甲醇;甲酸;直接甲醇燃料电池;Pt-Ru/C催化剂     

离子色谱法同时分析董酒中的有机酸与无机阴离子

研究了用离子色谱法同时分析董酒中可离解性有机酸和无机阴离子。首次采用邻苯二甲酸氢钾和邻苯二甲酸的混合水溶液作淋洗剂,改善了分离效果,提高了检测灵敏度。所建立的方法无需进行样品前处理,无干扰,有一定的实用价值。     

Determination of citric acid in fermentation media by pyrolysis mass spectrometry

Rapid and sensitive determination of citric acid in fermentation media by pyrolysis mass spectrometry (Py–MS) is proposed. Owing to high specificity of this method, distinguishing the citric acid from the matrix and by-products formed in the Krebs cycle is possible. Selected ion monitoring (SIM) mode is used for quantitative measurements, in which mass to charge (m/z) values of 175 of citric acid and 138 of 3-nitroaniline as internal standard are chosen. Limit of detection (LOD) for this method has been found to be 1 ng ml⁻¹ and the linear working range was 10 ng ml⁻¹–100 mg ml⁻¹. Relative standard deviation (R.S.D.) of the method for five replicates was 0.84%. Results of Py–MS are compared with those obtained by UV–vis spectrophotometric method. Also, factor analysis is used for evaluating the influence of pH, molasses concentration, time and shaker intensity on the production of citric acid by Aspergillus niger.     

Determination of tungsten in silicates and natural waters

Coprecipitation with hydrous manganese dioxide is used for the concentration of tungsten from natural waters (including sea water) and from solutions prepared from silicate rocks and sediments by hydrofluoric acid attack. After dissolution of the hydrous manganese dioxide precipitate in acidified sulphur dioxide solution, cation excliange is used to separate tungsten and molybdenum from other coprecipitated elements, hydrogen peroxide being used as eluant. Molybdenum is separated from tungsten by extraction of its dithiol complex from 24 N hydrochloric acid medium containing citric acid and can be determined photometrically. After destruction of citric acid, tungsten is determined photometrically with dithiol. The overall cliemical yield of th analytical process is 94±1%. The standard deviation of the method is ±0.010 μg for sea water (0.116 μg W/l) and ca 0.05 μg/g for siliceous sediments containing 0.5–1.0 μg W/g.     

Specific Differential Spectrophotdmetric Determination of Ascorbic Acid in Plants Using Ascorbate Oxidase

Abstract

A specific enzymic-differential spectrophatometric method is described and evaluated for the determination of ascorbic acid in vegetables and medicinal plants. It is based on the absorbance measurement at 593 nm of the complex of ferrous ion with 2,4,6-tris (pyridyl)-S-triazine, which is produced by reduction of ferric ion by ascorbic acid, versus a blank sample treated with ascorbate oxidase. The absorbance difference is linearly related to ascorbic acid from 10 to 100 ug/ml. A standard deviation of ±0.5 ug/ml (n=5) and a mean recovery of 101.47. (98.3–103.3%.) from spiked plant extracts, were found. The method was used to determine ascorbic acid in various plants of the Greek flora. Acacia cvanophvlla was found to be the richest source tested for ascorbic acid (89.6 mq/100 q of leaves). The method is very simple and can be used in routine analysis.     

Simple reversed-phase high-performance liquid chromatographic method for 13-cis-retinoic acid in serum.

An isocratic reversed-phase high-performance liquid chromatographic method for the analysis of 13-cis-retinoic acid in serum is developed. Sample preparation includes deproteination with acetonitrile-perchloric acid-acetic acid followed by centrifugation. 9-Methylanthracene is used as the internal standard. Chromatographic separation is achieved on a C18 column (Zorbax) using an acetonitrile-aqueous 0.5% acetic acid (85:15, v/v) eluent containing 0.05% (w/v) sodium hexanesulfonate. The limit of detection is 12 ng/ml in serum, using 0.5 ml samples. Quantitative recoveries and excellent intra-day and inter-day precision are reported.     

The use of stabilizers in the UV assay of ascorbic acid

Sodium thiosulphate (0.04%w/v) has been used to stabilize ascorbic acid in aqueous medium. The method has been used to assay ascorbic acid in commercial tablet preparations. It is very accurate, precise and reproducible. It compares favourably with official titrimetric method. The method is simple and can be adopted for the routine assay of ascorbic acid in single component tablet formulations.     

Simultaneous analysis of oxidized and reduced glutathione in cell extracts by capillary zone electrophoresis

Glutathione (GSH) and glutathione disulfide (GSSG) levels in cells constitute a thiol redox system. They can be used as an indicator of oxidative stress of the cell. In this study, a capillary zone electrophoresis (CZE) method is described that enables quantitation of GSH and GSSG from cellular extracts. The CZE buffer used was 20 mM ammonium acetate containing 5% (v/v) acetic acid at pH 3.1 in conjunction with a polybrene coated capillary operated in reverse polarity mode. Effects of different acids used to prepare cell samples were investigated on CZE performance. The acids include meta phosphoric acid (MPA), trichloroacetic acid (TCA), phosphoric acid (PA) and sulfosalicylic acid (SSA) and are used to stabilize GSH and GSSG before performing CZE analysis. The method features a limit of detection of 4 microM and a limit of quantitation of 12 microM for both GSSG and GSH and recoveries of 94% for GSH and 100% for GSSG. Quantitative analysis of GSSG and GSH in HaCaT cell extracts (5% SSA, w/v) was performed with this method and changes in the ratio of GSH to GSSG in N-ethylmaleimide treated cell sample was observed by comparing with control cell samples.     

高效液相色谱法测定铬超富集植物李氏禾根系分泌物中的有机酸

建立了高效液相色谱（HPLC）测定Cr超富集植物李氏禾根系分泌物中低相对分子质量有机酸的分析方法。采用XSelect HSS T3色谱柱（250 mm×4.6 mm,5 μm,Waters）,以40 mmol/L磷酸二氢钾-磷酸缓冲溶液（pH=2.40）作流动相,流速1.0 mL/min,柱温25℃,在波长205 nm处检测。该方法在13 min内简便快速地分离出8种有机酸（草酸、酒石酸、苹果酸、乳酸、甲酸、乙酸、马来酸和柠檬酸）,且峰形良好。有机酸的检出限（LOD）为0.12~12.32 mg/L;草酸的加标回收率为73.15%,其他有机酸的加标回收率为94.54%~109.98%。李氏禾的根系分泌物中各有机酸含量分别为酒石酸（130.90±1.44）μg/g（根干重）、苹果酸（1031.34±4.38）μg/g（根干重）、乳酸（65.54±1.01）μg/g（根干重）、马来酸（0.96000±0.00367）μg/g（根干重）和柠檬酸（201.50±1.13）μg/g（根干重）。该方法简便快速,灵敏可靠,适用于植物根系分泌物样品中有机酸的测定。     

Elimination of amino acid interferences in the chiral ligand-exchange chromatographic analysis of lactic acid enantiomers in wine

Chiral ligand-exchange liquid chromatography is used to identify and quantitate lactic acid enantiomers in wines that have or have not undergone malolactic fermentation. The stationary phase is (R)-penicillamine, which is bound lipophilically to a C18 bonded silica matrix. The mobile phase is 1mM copper sulfate, and the detection mode is ultraviolet. Serious interference from (S)-aspartic acid and other amino acids is eliminated by the use of propanesulfonic acid-type cation exchange solid-phase extraction cartridges prior to chromatographic analysis. Lactic acid enantiomers in wine are quantitated in the range of 10 to 500 mg/L. The detection limit is 3 mg/L. The method is also successful in the determination of lactic acid enantiomers in certain beers (e.g., lambic beers), kim-chi, sauerkraut, and various yogurts.     

Role of the Hydroxyl Radical-Generating System in the Estimation of the Antioxidant Activity of Plant Extracts by Electron Paramagnetic Resonance (EPR)

The scavenging activity of hydroxyl radicals, produced by the Fenton reaction, is commonly used to quantify the antioxidant capacity of plant extracts. In this study, three Fenton systems (Fe/phosphate buffer, Fe/quinolinic acid and Fe/phosphate buffer/quinolinic acid) and the thermal degradation of peroxydisulfate were used to produce hydroxyl radicals; the hydroxyl radical scavenging activity of plant extracts (ginger, blueberry juices and green tea infusion) and chemical compounds (EGCG and GA) was estimated by spin trapping with DMPO (5,5-dimethyl-1-pyrroline N-oxide) and EPR (Electron Paramagnetic Resonance) spectroscopy. Phosphate buffer was used to mimic the physiological pH of cellular systems, while quinolinic acid (pyridine-2,3-dicarboxylic acid) facilitates the experimental procedure by hindering the spontaneous oxidation of Fe(II). The EC₅₀ (the concentration of chemical compounds or plant extracts which halves the intensity of the DMPO–OH adduct) values were determined in all the systems. The results show that, for both the chemical compounds and the plant extracts, there is not a well-defined order for the EC₅₀ values determined in the four hydroxyl radical generating systems. The interactions of phosphate buffer and quinolinic acid with the antioxidants and with potential iron-coordinating ligands present in the plant extracts can justify the observed differences.     

Rapid high-performance liquid chromatography-electrospray ionization tandem mass spectrometry method for qualitative and quantitative analysis of virgin olive oil phenolic metabolites in human low-density lipoproteins

A rapid method for detection and quantification of metabolites of specific olive oil phenolic compounds (hydroxytyrosol monoglucuronide, hydroxytyrosol monosulfate, tyrosol glucuronide, tyrosol sulfate and homovanillic acid sulfate) in low-density lipoprotein (LDL) fractions by solid-phase extraction (SPE) and high-performance liquid chromatography coupled to electrospray ionization tandem mass spectrometry (HPLC/ESI-MS/MS) is described. A 3 microm particle size fast C18 Luna column, 5 cm x 2.0 mm I.D., was used at a flow rate of 0.6 mL/min with a mobile phase consisting of 0.1% (v/v) formic acid (A) and acetonitrile (B). A linear gradient profile was used for separation at column temperature 40 degrees C. The proposed chromatographic procedure is rapid without loosing its separation efficiency and sensitivity. Validation proofs were carried out for the method described, showing a linear system (r>0.99) and a recovery of 81.9 and 101.3% for hydroxytyrosol and homovanillic acid, respectively. The results show that this method is effective and can be used in routine analysis.     

高效液相色谱法测定毛樱桃中维生素C含量

建立了高效液相色谱(HPLC)测定毛樱桃中维生素C的主要成分L-抗坏血酸和D-异抗坏血酸的方法. 以0.05 mol/L磷酸溶液∶甲醇(体积比为98∶2)作为流动相,紫外检测波长245 nm,柱温25 ℃,流速0.70 mL/min. 获得L-抗坏血酸、D-异抗坏血酸标准曲线线性较好(r为1.0),精密度(RSD)为0.6%. L-抗坏血酸加标回收率为90.83%~92.52%,D-异抗坏血酸加标回收率为91.93%~92.99%. 试验结果表明,方法测定维生素C操作简单、提取速度快、灵敏度高、回收率好,测得L-抗坏血酸的含量为8.24 mg/100 g,D-异抗坏血酸未检测出. 方法可适用于检测其他与毛樱桃相似的果蔬中L-抗坏血酸、D-异抗坏血酸的含量.     

毛细管电泳法同时分析水、乳、膏类化妆品中5种有机酸

建立了毛细管电泳同时分析5种有机酸的间接紫外检测法。优化了背景电解质溶液中表面活性剂十四烷基三甲基溴化铵（TTAB）的浓度和溶液pH。优化后的电泳分析条件如下：含0.4 mmol/L TTAB的15 mmol/L邻苯二甲酸氢钾溶液为背景电解质（pH 5.6）；分离电压-15 kV；检测波长254 nm；分离温度25℃；进样压力5 kPa；进样时间5 s。在此条件下，可在6 min内完成5种有机酸的同时分离检测，线性范围为甲酸15~600 mg/L、苹果酸30~800 mg/L、柠檬酸20~700 mg/L、乙醇酸40~500 mg/L和乳酸30~5000 mg/L，线性相关系数为0.9983~0.9998；检出限为0.1~2.0 μg/g。该方法可用于检测水状、乳状、膏状3类化妆品中的5种有机酸。在3个加标水平下，有机酸分析的回收率为95.0%~101.6%，RSD在2.0%以内。该方法操作简单，分析快速，安全环保，灵敏度高，重现性好，有望用于化妆品生产和保存过程中有机酸的监测。     

聚天冬氨酸的合成研究

以L-天冬氨酸为原料,磷酸为催化剂,在不同溶剂中进行缩聚反应,合成中间体聚丁二酰亚胺(PSI),当混合溶剂为m三甲苯／m环丁砜=7／3时,可得到较高分子量的PSI。当催化剂与单体的质量比为0．14时,分子量达到最大值。将PSI碱解得到聚天冬氨酸。     

Plutonium(III) oxidation under α-irradiation in nitric acid solutions

Plutonium(III) oxidation under high energy α-irradiation in nitric acid solutions has been studied relative to concentrations of both nitric acid (0.12–2.9 mol/l) and plutonium (1.4–10 mmol/l) using spectrophotometric techniques. Curium-244 has been used as the basic alpha-irradiation source. It has been stated that in solutions with nitric acid concentrations lower than 0.5 mol/l plutonium(III) does not oxidize completely. In the course of the process the formation of a plutonium(IV) peroxide complex is observed. Increase in the nitric acid concentration results in that in both the rate and degree of plutonium(III) oxidation. When c_{HNO 3} is higher than 0.5 mol/l the peroxide complex does not form and the process assumes an autocatalytic character. It has also been shown that plutonium(III) oxidation kinetics is significantly affected by nitrous acid, one of the nitrate ion radiolysis products. To describe plutonium chemical transformations under irradiation in nitric acid solutions, a kinetic scheme is proposed. The calculations have been carried out on a BESM-6 computer; a satisfactory agreement between the calculated and experimental data has been obtained.     

The determination of silver in sulphide minerals by atomic absorption spectrophotometry

Silver can be determined in sulphide minerals by atomic absorption spectrophotometry after decomposition with nitric and/or sulphuric acid with addition of tartaric acid to prevent precipitation of antimonic acid. The amount of silver retained in the residue is negligible if the acids used are completely chloride-free or if mercury(II) nitrate is added.     

直接甲酸燃料电池用碳载铁卟啉-Au复合阴极催化剂的性能

研究了用于直接甲酸燃料电池(DFAFC)的碳载铁卟啉(FeTPP/C)、金复合阴极催化剂(FeTPP-Au/C)对氧还原的电催化性能和抗甲酸能力。结果表明,FeTPP-Au/C催化剂对氧气还原反应的电催化活性要远优于碳载铁卟啉(FeTPP/C)和碳载Au(Au/C)催化剂。而且,FeTPP-Au/C催化剂对甲酸氧化没有催化活性,因此,FeTPP-Au/C催化剂也有很好的抗甲酸能力。所以,FeTPP-Au/C催化剂适合作为DFAFC的阴极催化剂。