Kinetic-spectrophotometric determination of ascorbic acid by inhibition of the hydrochloric acid-bromate reaction

A new analytical method was developed for the determination of ascorbic acid in fruit juice and pharmaceuticals. The method is based on its inhibition effect on the reaction between hydrochloric acid and bromate. The decolourisation of Methyl Orange by the reaction products was used to monitor the reaction spectrophotometrically at 510 nm. The linearity range of the calibration graph depends on bromate concentration. The variable affecting the rate of the reaction was investigated. The method is simple, rapid, relatively sensitive and precise. The limit of detection is 7.6 x 10(-6) M and calibration rang is 8 x 10(-6)-1.2 x 10(-3) M ascorbic acid. The relative standard deviation of seven replication determinations of 8 x 10(-6) and 2 x 10(-5) M ascorbic acid was 2.8 and 1.7%, respectively. The influence of potential interfering substance was studied. The method was successfully applied for the determination of ascorbic acid in pharmaceuticals.     

Spectrophotometric determination of copper with hydrochloric acid

A procedure is proposed whereby copper may be determined spectrophotometrically by means of the very near infrared absorption of its complex ion with hydrochloric acid. Only stannous and ferrous ions are serious interferences and they may be oxidized with nitric acid or with ammonium persulfate to avoid such interference. The method is simple and rapid and is capable of reasonably good precision and accuracy.     

Spectrophotometric determination of tryptophan by reaction with nitrous acid

The heterocyclic nucleus in tryptophan is oxidised by nitrous acid at elevated temperature to produce a phenolic intermediate which further reacts with nitrous acid to form a nitro compound that has a golden yellow colour in alkaline medium. The maximum absorbance is obtained at 400 nm with maximum molar absorptivity of 9.44 x 10(3) l.mole(-1). cm(-1). Derivatives of tryptophan such as indole-3-acetic acid, tryptamine and tryptophanamide, as well as indole, produce the same colour, but some others, e.g., 5-hydroxytryptamine and 5-hydroxyindole-3-acetic acid do not give the colour reaction. A plausible mechanism is proposed to explain this behaviour.     

Spectrophotometric reaction rate method for the determination of osmium by its catalytic effect on the oxidation of gallocyanine by bromate

A simple kinetic spectrophotometric method was developed for the determination of osmium. The method is based on the catalytic effect of osmium as osmium tetroxide on the oxidation of gallocyanine by bromate at pH 7. The reaction is monitored spectrophotometrically by measuring the decreasing absorbance of gallocyanine at 620 nm by the fixed-time method. A detection limit of 0.01 ng/ml and linear calibration curve from 0.1 to 100 and from 100 to 1200 ng/ml Os(VIII) is reported. The relative standard deviation for 0.0100 microg/ml Os(VIII) is 0.8% (N = 10). The method is free from most interferences. Osmium in synthetic samples is determined by this method, with satisfactory results.     

Highly sensitive spectrophotometric kinetic determination of vanadium by catalysis of the gallic acid-bromate reaction

Conditions are described for improving the speed and sensitivity of this catalytic determination of vanadium. The reaction of 0.018 M gallic acid with 0.96 M sodium bromate at pH 3.8 and double-beam spectrophotometric measurement at 380 nm are recommended. The calibration curves are obtained by the tangent (2-point) and fixed-time (single-point) method. The highest practical sensitivity at 22–30°C was ca. 40 pg for an absorbance change of 0.0005, 50 times better than previously. The detection limit was ca. 0.5 ng of vanadium. Reaction at 50°C gave even better sensitivity.     

Catalytic determination of trace amounts of vanadium by means of the chromotropic acid-bromate reaction

A catalytic reaction-rate method is described for the determination of trace amounts of vanadium; the method is based on the vanadium-catalysed oxidation of chromotropic acid by bromate. The reaction was followed spectrophotometrically by measuring the rate of change in absorbance of chromotropic acid at 430 nm. The method is sensitive, rapid and simple, and allows determination of as little as 5 ng of vanadium. Of the many ions examined, iron(III), copper and tungsten(VI) interfered seriously at 100-fold concentrations. The relative standard deviation for 20 ng of vanadium (10 determinations) was 2.5%.     

Spectrophotometric reaction rate method for the determination of molybdenum by its catalytic effect on the oxidation of pyrogallol red with hydrogen peroxide

A kinetic spectrophotometric method for the determination of molybdenum is based on its catalytic effect on the oxidation of pyrogallol red with hydrogen peroxide. The decrease of the absorbance of pyrogallol red in the presence of hydrogen peroxide with time from 0.5 to 4.5 min is proportional to the concentration of Mo(VI) over the range 0.010–0.500 μg/mL. The limit of detection is 0.008 μg Mo/mL. The precision and the effect of the presence of more than forty ions on the molybdenum determination are reported. Probable interferences are completely removed by a cation exchange resin. The procedure was successfully applied to the determination of molybdenum in plant materials and steels. Received: 28 April 1997 / Revised: 16 June 1997 / Accepted: 18 June 1997     

Spectrophotometric reaction rate method for the determination of molybdenum by its catalytic effect on the oxidation of pyrogallol red with hydrogen peroxide

A kinetic spectrophotometric method for the determination of molybdenum is based on its catalytic effect on the oxidation of pyrogallol red with hydrogen peroxide. The decrease of the absorbance of pyrogallol red in the presence of hydrogen peroxide with time from 0.5 to 4.5 min is proportional to the concentration of Mo(VI) over the range 0.010–0.500 μg/mL. The limit of detection is 0.008 μg Mo/mL. The precision and the effect of the presence of more than forty ions on the molybdenum determination are reported. Probable interferences are completely removed by a cation exchange resin. The procedure was successfully applied to the determination of molybdenum in plant materials and steels. Received: 28 April 1997 / Revised: 16 June 1997 / Accepted: 18 June 1997     

氧化苯胺蓝褪色光度法测微量锰

研究了在H2SO4介质中,锰(VII)能氧化苯胺蓝使其褪色,且褪色的程度随锰量变化呈线性关系,据此建立了测定锰的光度分析方法。实验测定波长为602nm,表观摩尔吸光系数为 2.72?104 L?mol-1?cm-1,锰的量在0 ~100?g/25mL范围内服从朗伯-比尔定律,茶叶中常见金属元素不干扰测定,方法在用于测定茶叶中微量锰时,其相对标准偏差在1.7%～2.9%之间,回收率为100.8%～103.2%     

The effect of barbituric acid concentration in the spectrophotometric determination of cyanide and thiocyanate by the pyridine-barbituric acid method

Summary The König reaction forms the basis of many analytical methods including those for the determination of chlorine, nicotinic acid, thiocyanate and cyanide. The colorimetric methods have, however, been plagued with various problems such as the use of hazardous, often carcinogenic compounds, and the instability of the final color formed as well as of the color reagent itself.Using a mixture of pyridine, hydrochloric acid and barbituric acid as the color reagent, the present study shows the effect of barbituric acid concentration on the intensity and stability of the color complex. The problems associated with the use of barbituric acid can be attributed mainly to the high concentration used by previous workers. A color reagent containing about 0.1% (w/v) barbituric acid shows marked improvements in color intensity and stability as well as reagent stability.     

Spectrophotometric determination of trace amounts of selenium with catalytic reduction of bromate by hydrazine in hydrochloric acid media

A method is presented for the determination of selenium, based on the catalytic effect of selenium(IV) on the reduction reaction of BrO(-)(3) by N(2)H(4).2HCl. The decolourization of Methyl Orange by the reaction products was used to monitor the reaction spectrophotometrically at 525 nm. This method is precise, highly sensitive, simple, rapid, widely applicable and selective for the determination of selenium(IV) and total selenium. The variables which affected the reaction rate were fully investigated and the optimum conditions were established. Selenium, as low as 1 ng/ml, can be determined by this method. The relative standard deviation of 20 ng of selenium was 0.94% (N = 10). The method was applied to the determination of Se(IV) in a health-care product.     

利用荷移反应分光光度法测定注射液中的盐酸利多卡因

采用分光光度法研究了电子受体2,3-二氯-5,6-二氰基-1,4-对苯醌(DDBQ)与电子供体利多卡因(LD)的荷移反应,发现DDBQ与LD在乙腈中生成稳定的离子缔合物,并通过Job's plot确定DDBQ和LD的摩尔比为1:1.LD与DDBQ在587nm处形成强特征吸收峰.据此建立了一种测定注射液中LD含量的荷移分...     

Spectrophotometric determination of papaverine hydrochloride by reaction with phloxin

A new withasteroid — vamonolide — has been isolated from the epigeal part ofPhysalis angulata L. (Solanaceae). On the basis of spectral characteristics, its structure has been established as 5,14-dihydroxyl-l-oxo-6,7-epoxy-20R,22R-with-2-enolide.Institute of the Chemistry of Plant Substances, Uzbek SSR Academy of Sciences, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 856–858, November–December, 1987.     

Spectrophotometric determination of papaverine hydrochloride by reaction with phloxin

The optimum conditions for the formation of a complex of papaverine hydrochloride with phloxin have been determined: pH 2.5–3.2. A procedure has been developed for the spectrophotometric determination of papaverine hydrochloride. The sensitivity of the determination is 0.4 µg/ml.Vitebsk Medical Institute. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 836–838, November–December, 1988.     

Spectrophotometric determination of uranium(vi) by the azide reaction

Azide has been investigated as a spectrophotometric reagent for uranium(VI). The system is more sensitive than the thiocyanate reaction. It obeys Beer's law in the range 2–180 p.p.m. of uranium. The colour is sensitive to hydrogen ion concentration ; maximum absorbance and stability are attained at pH 5–5.5. Iron(III) interferes seriously, but can be masked by EDTA. Fe⁺², Cr⁺³, Ni⁺², Th⁺⁴, Cr₂O₇^-2, WO₄^-2, VO₃^- and F^- interfere. The deep yellow colour cannot be extracted with organic solvents. A mono-azido-uranium(Vl) ion is present in dilute solutions; its dissociation constant is 2.3 ±20.27·10^-3.