Spectrophotometric determination of trimethoprim by oxidation in drug formulations

A spectrophotometric determination of trimethoprim is described based on the reaction of its amine group with persulfate which acts as a strong oxidizing agent in alkaline media. The reaction produces a stable yellow colored compound after heating in a boiling water bath for 30 min. At λ_max 355 nm, Beer’s law is obeyed in the concentration range 10–60 μg ml^–1 with a molar absorptivity of 2.7 × 10³ l mol^–1cm^–1. The method is applied to formulations with sulfamethoxazole. Received: 30 July 1996 / Revised: 16 October 1996 / Accepted: 22 October 1996     

The determination of some aliphatic alcohols and aldehydes by oxidation with acid potassium dichromate

The oxidation of n-propanol and n-butanol and the corresponding aldehydes by dilute acid potassium dichromate has been investigated. Some carbon -carbon bond fission occurs, and it has been shown that this takes place via the enol form of the aldehyde formed in the first stage of the oxidation. However, the proportion of this degradation is constant over a wide range of conditions and the method is capable of being used for the quantitative determination of simple aliphatic alcohols and aldehydes.     

铁氰化钾氧化分光光度法测定左旋多巴含量

研究了铁氰化钾与左旋多巴之间的氧化反应所引起的吸收光谱的变化.实验发现,碱性溶液中铁氰化钾氧化左旋多巴生成红色化合物,其最大吸收波长为475nm,铁氰化钾与左旋多巴的物质的量之比为2∶1.体系的吸光度与左旋多巴的浓度在3.2~54.4mg/L范围内呈良好的线性关系,线性回归方程A=-0.038 88+0.020 8c(mg/L),相关系数r=0.999 2,表观摩尔吸光系数ε=5.1×103 L·mol-1cm-1.该方法的检出限为2.32mg/L,对浓度为16.0mg/L的左旋多巴进行平行11次测定,其相对标准偏差为0.3%.据此建立了测定左旋多巴的新方法,能够直接用于市售的左旋多巴片中左旋多巴含量的测定,回收率为96.7%~104.4%.     

Spectrophotometric determination of paracetamol with iodylbenzene

Paracetamol (N-acetyl-4-aminophenol) has been determined spectrophotometrically by its oxidation with iodylbenzene in acetone to produce the yellow-orange N-acetyl-1,4-benzoquinoneimine, which attains maximum colour intensity within 1 min and absorbs maximally at 430 nm. The maximum molar absorptivity is 1.58 x 10(3) l.mole(-1).cm(-1). The method is simple and rapid and has been found to be unaffected by the presence of salicylamide, oxyphenbutazone, acetylsalicylic acid, dipyrone and a number of other excipients.     

Spectrophotometric determination of verapamil hydrochloride in drug formulations with chloramine-T as oxidant

A new spectrophotometric method is described for the determination of verapamil hydrochloride, based on its oxidation with chloramine-T in hydrochloric acid medium. It produces a yellow colored compound with maximum absorbance at 425 nm. Beer's law was obeyed in the concentration range 0-340 micro g mL(-1) with molar absorptivity 2 x 10(3) L mol(-1) cm(-1) and RSD 0.3-0.82%. All variables were studied to optimize the reaction conditions. No interferences were observed from the common excipients present in the formulations. The method has been applied successfully to the determination of the drug in pharmaceutical preparations. Statistical comparison of the results with those from the reference method reveals excellent agreement and confirms that accuracy and precision are not significantly different.     

重铬酸钾氧化法合成2-吡啶甲酸的研究

研究了以2-甲基吡啶为原料,以重铬酸钾为氧化剂,利用化学氧化法合成2-吡啶甲酸的反应条件.考察了反应温度、反应物2-甲基吡啶的浓度和与重铬酸钾的浓度比例、硫酸浓度和反应时间对产率、转化率及选择性的影响,其产物用红外、元素分析和熔点分析表征.实验表明,最佳反应条件:反应温度105℃,2-甲基吡啶摩尔浓度为0.075mol/L,重铬酸钾与2-甲基吡啶浓度比为2∶1,硫酸浓度为9 mol/L,反应时间为2 h,其转化率可达97.6%,2-吡啶甲酸的色谱产率可达87.7%,选择性为89.8%.     

Spectrophotometric determination of paracetamol with microwave assisted alkaline hydrolysis

A novel and rapid spectrophotometric method for the determination of paracetamol is proposed in this paper. The proposed method is based on the microwave assisted alkaline hydrolysis of paracetamol to p-aminophenol that reacts with S2- in the presence of Fe3+ as oxidant to produce a methylene blue-like dye having an absorptivity maximum at 540 nm. The experiment showed that paracetamol could be hydrolysed quantitatively to p-aminophenol in only 1.5 min under radiation power 640 W using a microwave in NaOH medium. The system obeys Beer's law in the range of 0-3.0 x 10(-4) mol l(-1) paracetamol. The molar absorptivity and Sandell's sensitivity were found to be 3.2 x 10(-3) l mol(-1) cm(-1) and 0.047 microg cm(-2), respectively. The relative standard deviation (n=11) was 1.7% for 8.0 x 10(-5) mol l(-1) paracetamol. The method has been applied successfully to analysis of paracetamol in pharmaceutical preparation.     

Spectrophotometric determination of trace nitrite based on catalytic oxidation of thionine by potassium bromate

A kinetic method for the determination of trace nitrite (7 × 10^?9–1.2 × 10^?6 M) based on its catalytic effect on the reaction between potassium bromate and thionine in strongly acidic media is reported. The reaction is monitored spectrophotometrically by measuring the decreasing colour of thionine at 602 nm by the fixed-time method. At a given time of 5 min at 30°C, the detection limit is 2 × 10^?9 M (0.001 absorbance ratio, b = 1 cm) and the relative standard deviation for 1 × 10^?6 M nitrite is 2.6% (n = 6). The method is free from most interferences, especially from large amounts of nitrate. The procedure was successfully applied to the determination of trace nitrite in natural water and sausage samples without preconcentration and separation.     

Spectrophotometric determination of dopamine in pharmaceutical formulations

A new spectrophotometric method was developed for the estimation of dopamine. The method is based on the bromination of the dopamine with a solution of excess brominating mixture. After bromination, the excess brominating mixture is treated with potassium iodide to produce a yellow solution. The absorbance of yellow solution was measured at 350 nm on a Spectronic 1001 spectrophotometer against distilled water as a blank.From Zhurnal Analiticheskoi Khimii, Vol. 60, No. 3, 2005, pp. 2842285.Original English Text Copyright © 2005 by Rami Reddy, Sreedevi, Prabhavathi, Chakravarthy.This article was submitted by the authors in English.     

铁氰化钾分光光度法测定头孢他啶

建立了K3[Fe(CN)6]光度法测定头孢他啶的方法。研究表明:控制溶液pH 4.0左右,头孢他啶可以将Fe(III)还原为Fe(II),还原生成的Fe(II)与K3[Fe(CN)6]反应生成可溶性的普鲁士蓝,其最大吸收波长为735 nm。头孢他啶在0.05～7.2μg/mL范围内与吸光度呈良好的线性关系,线性回归方程A=0.03414+0.07334c(μg/mL),线性相关系数R=0.9992,表观摩尔吸光系数ε=4.0×104 L/(mol.cm),检出限为0.026μg/mL。本法能直接用于注射用头孢他啶的含量的测定,结果满意。     

Spectrophotometric determination of azathioprine in pharmaceutical formulations

Four simple and sensitive visible spectrophotometric methods (A–D) have been described for the assay of azathioprine (ATP) either in pure form or in pharmaceutical formulations. Methods A and B are based on the oxidation of ATP with excess N-bromosuccinimide (NBS) or chloramine-T (CAT) and determining the consumed NBS or CAT with a decrease in colour intensity of celestine blue (CB) (method A) or gallocyanine (GC) (method B), respectively. Methods C and D are based on the diazotisation of reduced azathioprine (RATP) with excess nitrous acid and estimating either the consumed nitrous acid (HNO₂) with cresyl fast violet acetate (CFVA) (method C) or by coupling reaction of the diazonium salt formed with N-1-naphthyl ethylene diamine dihydrochloride (NED) (method D). All of the variables have been optimized and the reactions presented. The concentration measurements are reproducible within a relative standard deviation of 1.0%. Recoveries are 99.2–100.3%.     

Spectrophotometric methods for determination of enalapril and timolol in bulk and in drug formulations

Two simple and accurate spectrophotometric methods for determination of timolol and enalapril maleate are described. The first method is based on chelate formation with palladium(II) chloride in buffered medium. The second method is based on the formation of the colored complex between palladium(II), eosin, and the two cited drugs using methylcellulose as surfactant to increase the solubility and intensity of the formed complexes. Under optimum conditions the complexes showed maximum absorption at 369.4 nm and 362.8 nm for timolol and enalapril maleate, respectively, in the first method and 552.2 and 550.6 nm for the second method. Apparent molar absorptivities were 1.8 x 10(3) and 1.3 x 10(3) and Sandell's sensitivities were 5.9 x 10(-4) and 2.7 x 10(-4) for timolol and enalapril maleate in the first method; in the second method molar absorptivities were 2.8 x 10(4) and 1.1 x 10(4) while Sandell's constants were 9.1 x 10(-3) and 2.3 x 10(-3) for timolol and enalapril maleate. The solutions of the complexes obeyed Beer's law in the concentration ranges 20-200 micro g mL(-1) and 50-300 micro g mL(-1) for timolol and enalapril maleate, respectively. In the second method, because the reaction was more sensitive the ranges were reduced to 1.6-16 micro g mL(-1) for timolol 8-56 micro g mL(-1) for enalapril maleate. The proposed methods were applied to the determination of the two drugs in their pharmaceutical formulation.     

The determination of cobalt by oxidation with potassium molybdicyanide

Cobalt has been determined titrimetrieally and coulometrically by oxidation of the bivalent ion with potassium molybdicyanide, K₃Mo(CN)₈, in ammoniacal medium. The break in potential at the equivalence-point is approximately 0.6 volt. Manganese is not oxidized stoichiometrically in citrate media, but the total of cobalt and manganese may be obtained in the presence of fluoride. Iron interferes when fluoride, but not when citrate is used as the complexing agent. The method, therefore, is not directly applicable to steels where both iron and manganese are present.     

FIA-fluorimetric determination of adrenaline in pharmaceutical formulations by oxidation with molecular oxygen

The fluorimetric determination of adrenaline is carried out in a continuous-flow assembly and by means of the molecular dissolved oxygen. The sample solution merges with an NaOH stream, then the resulting mixture is heated at 73 °C and led to the flow-cell of the fluorimeter. The flow-assembly is very simple and the procedure is quick (107 samples h^–1) reproducible (R.S.D. 0.6%), selective and suitable to be applied to determination of adrenaline in formulations. Calibrations graph are linear over the ranges 0.05–15 and 20–40 mgl^–1.     

Use of urea for eliminating chlorine formed in the determination of chromium by ammonium peroxodisulfate oxidation and potassium dichromate back titration

In the determination of Cr by (NH₄)₂S₂O₈ oxidation and K₂Cr₂O₇ back titration, urea was used instead of boiling to eliminate Cl₂ formed.     

Simultaneous determination of ascorbic acid, caffeine and paracetamol in drug formulations by differential-pulse voltammetry using a glassy carbon electrode

A simple, rapid and accurate method for the simultaneous determination of ascorbic acid, caffeine and paracetamol in drug formulations has been developed. Peak currents were measured with a glassy carbon electrode at +0.350, +0.618 and +1.425 V versus a saturated calomel electrode for ascorbic acid, paracetamol and caffeine, respectively. Perchloric acid (0.1 M) - methanol (1 + 1) was used both as a solvent and supporting electrolyte. The optimum modulation amplitude, pulse repeat time and scan rate of the polarographic analyser were found to be 50 mV, 0.5 s and 5 mV s-1, respectively and the linear calibration ranges for ascorbic acid, caffeine and paracetamol were 0-35, 0-50, and 0-55 micrograms ml-1, respectively. The relative standard deviations for 9.30 micrograms ml-1 of ascorbic acid, 8.50 micrograms ml-1 of caffeine and 7.30 micrograms ml-1 of paracetamol were 1.3, 2.5 and 0.7%, respectively. Results are reported for several commercially available drugs.     

Spectrophotometric determination of urea in dermatologic formulations and cosmetics

A rapid, relatively sensitive, and low-cost method for the determination of water-soluble urea content in dermatological therapy products and cosmetics is proposed using a new spectrophotometric assay with water as the only extraction solvent. Spectrophotometric methods involve addition of a known excess of bromate to urea in an acid medium, followed by the determination of residual bromine and chlorine reacting with methyl orange and measurement of absorbance at 505 nm. The absorbance increases linearly with urea concentration (r = 0.9998). The systems obey Beer's law for 6 - 90 microg ml(-1). The calculated apparent molar absorbance values are found to be 4.537 x 10(3) dm(3) mol(-1) cm(-1) and the Sandell's sensitivity is 0.013 microg cm(-2). The variables affecting the rate of the reaction were investigated. The relative standard deviation for five-replication determination of 60 microg ml(-1) urea was 2.1% and the detection limit of the method is 0.34 ng ml(-1).