Catalytic kinetic spectrophotometry for the determination of trace amount of oxalic acid in biological samples with oxalic acid-rhodamine B-potassium dichromate system

A new catalytic kinetic spectrophotometric method was proposed for determining trace oxalic acid based on the catalytic effect of oxalate on the oxidation of potassium dichromate with rhodamin B in 0.10 M of sulfuric acid. Good linearity is obtained over the concentration range 0.40-6.0 microg/mL of oxalic acid. After the reactions of the catalytic and non-catalytic systems were terminated by using 2.00 mL of 4 M sodium hydroxide solution, they can be stable for 3 h at room temperature. The apparent activation energy of the catalytic reaction is 12.44 kJ/mol. The effect of 50 coexisting substances was observed. The method was used to determine trace oxalic acid in tea, spinach and urine samples with satisfactory results.     

Catalytic Kinetic Determination of Micro Amounts of Oxalic Acid by Second-Order Derivative Oscillopolarography

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A new chemically amplified electrochemical system for the detection of biological affinity reactions: direct and competitive biotin assay

Quantitation of biological affinity reactions by a newly developed chemically amplified electrochemical detection method was demonstrated with the biotin-avidin binding pair. In the method, ruthenium tris(2,2'-bipyridine)(Ru-bipy) was used as an electrochemical signal-generating tag. Its oxidation current on an indium tin oxide (ITO) electrode was amplified with a sacrificial electron donor, oxalate. Because oxalate itself produced negligible current on the electrode, the signal-to-background ratio was greatly enhanced in comparison with other chemical amplification systems. Although the Ru-bipy/oxalate redox couple has been employed previously in electrochemiluminescent and photoelectrochemical detection, its use in a catalytic amperometric detection of biological binding assays has not been reported. To implement the method in the detection of biotin-avidin recognition, avidin was immobilized on an ITO electrode, and was reacted with biotin in solution. Immobilization of avidin by passive adsorption was found to be relatively stable under the condition of the affinity reaction. In the direct assay, biotin labelled with Ru-bipy was recognized by avidin and accumulated on the electrode surface, which was then detected electrochemically in the presence of oxalate. A linear relationship between electrochemical current and biotin concentration was obtained in the range of 1-300 ng mL(-1). In the competitive assay, a mixed solution of unlabelled biotin (the analyte) of various concentrations and 100 ng mL(-1) labelled biotin was reacted with avidin on the surface. As the concentration of the unlabelled biotin increased, less labelled biotin bound to avidin, leading to a reduction in the electro-catalytical response of Ru-bipy. A detection limit of 1 ng mL(-1) biotin was obtained in the competitive assay, which is close to the sensitivity of some enzyme-labelled amperometric assays.     

The role of direct oxalate oxidation in electrogenerated chemiluminescence of poly(4-vinylpyridine)-bound Ru(bpy)2Cl/oxalate system on indium tin oxide electrodes

The electrochemical and electrogenerated chemiluminescence (ECL) properties of indium tin oxide (ITO) electrodes modified with poly(4-vinylpyridine) (PVP)-bound Ru(bpy)₂Cl⁺ (where bpy = 2,2′-bipyridine) have been studied. In a sodium oxalate solution, two irreversible oxidation waves as well as two ECL emission waves were observed during the potential scan in the range 0.4-1.4 V (versus Ag/AgCl/saturated KCl reference). The first ECL wave appeared at ca. 0.8 V, which was caused by the excited-state Ru^2+* generated through a bimolecular redox reaction between electrogenerated Ru³⁺ and the strong reducing agent, C⁻O₂. The latter was formed via a Ru³⁺-mediated oxidation of oxalate. Direct oxidation of oxalate was not involved in the first ECL process. The second ECL wave started at ca. 1.1 V, which was also from the excited-state Ru^2+* generated via the redox reaction between Ru³⁺ and C⁻O₂. However, both direct and Ru³⁺-mediated oxidation of oxalate contributed to the formation of C⁻O₂. The important role of the direct oxidation of oxalate in the ECL mechanism of PVP-bound Ru(bpy)₂Cl⁺/oxalate system was demonstrated. The relative contribution of direct oxidation of oxalate to the observed ECL depended upon the surface concentration of PVP-bound Ru²⁺, the concentration of oxalate and the electrode potential applied.     

Kinetic spectrophotometric method for the determination of trace amounts of oxalate by an activation effect.

A new, simple and inexpensive kinetic catalytic spectrophotometric method for the determination of oxalate is described. The method is based on an activation effect of oxalate on a catalytic effect of iron(II) on the oxidation of iodide by bromate. The reaction is monitored by measuring the absorbance of triiodide ion at lambda max = 352 nm. A calibration graph was obtained from 0.10 - 7.0 microg cm(-3) of oxalate with a detection limit of 0.080 microg cm(-3). The standard deviations for ten replicate determinations of 0.50, 1.0 and 5.0 microg cm(-3) of oxalate were 4.0, 2.6 and 1.8%, respectively. The applicability of the method was demonstrated by the determination of oxalate ion in real samples.     

Determination of oxalate and citrate in urine by capillary electrophoresis using solid‐phase extraction and capacitively coupled contactless conductivity based on an improved mini‐cell

A new method for the rapid determination of the metabolites oxalate and citrate in urine samples was based on capillary electrophoresis and capacitively coupled contactless conductivity detection coupled with solid‐phase extraction. The detection cell for capacitively coupled contactless conductivity detection was improved with a smaller inner volume (1.5 nL), reduced noise (0.2∼0.5 mV) and better reproducibility and durability. Under optimal conditions, oxalate and citrate can achieve baseline separation within 4 min and the detection limits (S/N = 3) for oxalate and citrate are about 44 and 244 ng/mL, respectively. The overall recovery is between 80.0 and 89.2%. This method offers a better choice for quantitative analysis of strong anions such as oxalate and citrate in diagnostic testing associated with human diseases.     

催化动力学光度法测定井水中痕量锰

研究了在 NH3· H2 O- NH4 Cl介质中锰催化过氧化氢氧化苋菜红的褪色反应及其动力学条件 ,测定了反应级数和表观活化能 ,建立了测定痕量锰的新方法。该方法的检出限为 2 .7× 1 0 -4 μg/m L Mn,线性范围为 0～ 2 .4μg/2 5m LMn。用于测定井水中痕量 Mn,与原子吸收法的测定结果一致。     

Determination of oxalate based on its enhancing effect on the oxidation of Mn(II) by periodate

A new kinetic spectrophotometric method for the determination of oxalate has been described, based on its enhancing effect on the oxidation of Mn(II) to MnO(4)(-), which is measured at 525 nm, by potassium periodate. Under the optimum conditions of 20 mugml(-1) Mn(II) in MnSO(4).H(2)O/0.015 moll(-1) H(3)PO(4)/0.013 moll(-1) sodium acetate and 3x10(-3) moll(-1) KIO(4) at 35 degrees C, calibration graphs in the range of 0.05-1.25 and 0.05-1.75 mugml(-1) oxalate concentration were obtained with detection limits of 27 and 5 ngml(-1) by the fixed time and the induction period methods, respectively. No serious interference was identified. The proposed method is simple, inexpensive, sensitive and accurate. The applicability of the method was demonstrated by the determination of the oxalate in spinach and urine samples.     

海藻异枝麒麟菜多糖抑制尿石盐草酸钙晶体生长的研究

采用扫描电子显微镜(SEM)、 红外光谱(FTIR)和X射线衍射(XRD)方法研究了从海藻异枝麒麟菜中提取的硫酸多糖(ESPS)对草酸钙(CaOxa)晶体生长的影响. 结果表明, 添加ESPS能抑制一水草酸钙(COM)的生长, 同时诱导二水草酸钙(COD)晶体的形成. 随着ESPS的质量浓度从0增加到0.03和0.50 mg/mL, COD的质量分数从0分别增加到10%和55%; COM的(1 01)晶面加强, (020)晶面减弱直至消失, 并从三维晶体转变为棱角圆顿的四角形片状晶体; COM和COD的尺寸均明显变小. 这些结果表明, ESPS是抑制CaOxa结石形成的一种潜在药物.     

钴(Ⅱ)-过氧化氢-DCF 偶氮胂体系催化动力学光度法测定中草药中痕量钴

在邻苯二甲酸氢钾-氢氧化钠介质中,以钴(Ⅱ)催化过氧化氢氧化 DCF 偶氮胂的褪色反应为指示反应,建立了测定痕量钴(Ⅱ)的新方法。测定了反应级数和表面活化能。方法的检出限为 2.6×10-12 g/mL,线性范围为 0～23 ng/10mL。用于测定几种中草药样品中的钴,相对标准偏差为 2.8%～3.0%。     

铬兰黑R-H_2O_2催化光度法测定痕量锌

研究了在稀硫酸介质中,Zn催化过氧化氢氧化铬兰黑R褪色反应,建立了测量痕量锌的新方法,Zn2+ 的检测限为1.5×10-10g/mL,线性范围为 0 ~ 3.1×10-2 mg / mL,该法用于测定头发中的痕量锌,结果满意。     

过硫酸钾氧化偶氮荧光桃红催化光度法测定痕量银

以过硫酸盐氧化偶氮类试剂催化动力学法测定银,多数线性范围较窄、选择性欠佳。本文建立了以偶氮荧光桃红作指示物质、α,α′-联吡啶作活化剂的催化光度法,测定痕量银检出限为1.0×10^-4μg/mL,线性范围2.0×10^-4～4.0×10^-2μg/mL,灵敏度高,选择性好。用于测定鄂铜矿中银,结果满意。采用自装的微机动力学数据处理系统,测试简便、准确。     

溴酸钾氧化亮绿SF催化光度法测定痕量亚硝酸根

本文基于亚硝酸根对溴酸钾氧化亮绿ＳＦ而使其褪色所起的催化作用，建立了高灵敏度催化吸光光度法测定痕量亚硝酸根的新方法，测定范围为０．０５－２０ｎｇ／ｍｌ，用于不同水样中亚硝酸根的测定，获得了满意结果。     

Quantitative Determination of Oxalic Acid Using Victoria Blue B Based on a Catalytic Kinetic Spectrophotometric Method

A sensitive catalytic method is developed for the spectrophotometric determination of oxalic acid. The procedure is based on the effect of oxalate on the oxidation of Victoria blue B by dichromate in dilute sulfuric acid medium. The reaction is quantitatively estimated by measuring the decrease in absorbance of Victoria blue B at the maximum wavelength of 610nm after quenching the reaction with tap water. The factors effecting the sensitivity and reproducibility of the reaction were studied. The method is not interfered with by foreign species generally associated with oxalate and oxalic acid. The described method is simple, specific, inexpensive and suitable for oxalic acid concentrations of between 0.06 and 9.0µgmL^–1. It was validated with satisfactory results by determining oxalic acid content in water extracts from plant materials such as spinach and Lathyrus sativus.     

Flow injection spectrophotometric determination of ultra trace amounts of oxalic acid

A new simple, sensitive and rapid catalytic-spectrophotometric method for the determination of oxalic acid has been described based on its catalytic effect on the redox reaction between dichromate and Brilliant cresyl blue in acidic media by means of a flow injection analysis method. The color change of Brilliant cresyl blue due to its oxidation was monitored spectrophotometrically at 625 nm. The calibration graph was linear in the range of 0.020-4.70 microg/mL oxalic acid with a limit of detection 0.005 microg/mL of oxalic acid. The relative standard deviation for ten replicate measurements of 0.020 microg/mL and 0.900 microg/mL was 2.2% and 1.7%, respectively. No serious interference was identified. Oxalic acid was determined in wastewater and in spinach by the proposed method with satisfactory results.     

Fractionation and redox speciation of antimony in agricultural soils by hydride generation--atomic fluorescence spectrometry and stability of Sb(III) and Sb(V) during extraction with different extractant solutions

This stability of Sb(III) and Sb(V) species was studied during single extraction from soils by water. EDTA, diluted H2SO4 and H3PO4, and oxalic acid/oxalate solutions, with and without ascorbic acid, were used as stabilizing reagent of both Sb species. Antimony redox speciation in soil extracts was performed by selective hydride generation-atomic fluorescence spectrometry. Simulated extraction procedures (without soil) showed that, except in oxalate medium, Sb(III) was oxidized to Sb(V), and this reaction was avoided with ascorbic acid. Recovery studies from a spiked agricultural soil showed that no oxidation but sorption of Sb(III) occurred during the extraction process in water and H2SO4 medium, and quantitative oxidation in EDTA and oxalate medium. With ascorbic acid, this oxidation was totally avoided in EDTA and partially avoided in oxalate solution. A new sequential extraction procedure was proposed and applied to the fractionation and redox speciation of antimony in agricultural soils, using EDTA + ascorbic acid, pH 7 (available under complexing and moderately reducible conditions); oxalic acid/oxalate + ascorbic acid (extractable in reducible conditions) and HNO3 + HCl + HF (residual fraction). The proposed extraction scheme can provide information about the availability and mobility of antimony redox species in agricultural soils.     

镧镍体系(LaNi5-xMx)吸氢化合物的研究(Ⅰ)——LaNi5的化学合成及吸氢性能

过渡金属氢化物因与氢能源的利用紧密有关,近年来在国际上引起极大注意。本文提出了吸氢化合物LaNi₅的一种新的合成方法--共沉淀还原法,并详细研究了反应过程。     

硫胺素-亚硝酸根体系的荧光性质研究及应用

研究了在碱性溶液中硫胺素（VB1）与亚硝酸根的荧光反应,建立了荧光光度法测定硫胺素的新方法。方法线性范围为1．28－324ng/mL,检出限0．52ng/mL,对15个浓度为100ng/mL的硫胺素溶液进行测定,相对标准偏差为1．4％。应用于药物中硫胺素的测定,回收率在96．5％－101．8％之间。     

土家族药物天葵化石汤提取液抑制草酸钙结石形成的化学模拟

采用扫描电子显微镜(SEM)和X射线衍射法(XRD)研究了土家族药物天葵化石汤(Tiankui)的提取液对尿石晶体草酸钙(CaOxa)成核、生长的抑制作用及其对二水草酸钙(COD)的稳定作用. 当Tiankui浓度小于30 mg/mL时, 主要生成一水草酸钙(COM), 但可使COM晶体棱角圆钝. 随着Tiankui浓度增加至45和75 mg/mL, 可分别诱导95%和100%的COD晶体生成. Tiankui还可以稳定COD在水溶液中的存在, 没有Tiankui存在时, COD在48 h内全部转化为COM晶体, 而在12 mg/mL Tiankui存在下, COD仅有20%转化. 从Tiankui提取液的活性组分、与草酸钙不同晶相间的吸附差异、化学配位等角度讨论了其抑制CaOxa生长和诱导稳定COD的化学基础.     

Analysis of hydroxide, inorganic sulphur species and organic anions in kraft pulping liquors by capillary electrophoresis

A new method has been developed for the determination of hydroxide, sulphide, thiosulphate, sulphate, sulphite, chloride, oxalate and formate in kraft green, white and black liquors by capillary electrophoresis. The method provides baseline resolution of all analytes of interest using an electrolyte composed of 10 mM sodium chromate and 2 mM tetradecyltrimethylammonium hydroxide. Separations are conducted under constant current conditions at 25 degrees C and analytes are quantified by indirect UV-detection at 275 nm. A brief, post run wash of the capillary with 0.5 M NaOH and water gave improved inter- and intra-run repeatability of both migration times and peak areas. Sulphide and other oxysulphur species were relatively stable in white and green liquors diluted in helium-sparged water. However, sulphide present in black liquor samples diluted in the same solvent underwent rapid oxidation to form sulphite and thiosulphate. thereby precluding the measurement of all three anions. We discovered that quinone-type compounds present in black liquor catalyze the oxidation of sulphide and that the addition of reduced glutathione at a concentration of I mg/mL during black liquor dilution completely stabilized sulphide, sulphite and thiosulphate for at least one hour, thus allowing for quantitative analysis of the analytes. A mechanism is proposed to explain the action of both quinones and that of glutathione. Results obtained by the new method compared well with those obtained by ion chromatography, titrimetry, and from spike-recovery experiments.