Indirect spectrophotometric method for determination of captopril using Cr(VI) and diphenylcarbazide

A spectrophotometric method for the indirect determination of captopril (CP) in pharmaceutical formulations is proposed. The proposed procedure is based on the oxidation of captopril by potassium dichromate and the determination excess oxidant on the basis of its reaction with diphenylcarbazide (DPC). Under the optimum conditions, a good linear relationship (r = 0.9997) was obtained in the range of 0.08-3.5 µg mL-1. The assay limits of detection and quantitation were 0.024 and 0.08 µg mL-1, respectively. The results obtained for captopril determination in pharmaceuticals using the proposed method and those obtained with the US Pharmacopoeia method were in good agreement at the 95% confidence level.

Estudo comparativo da eficiência da difenilcarbazida e do óleo de coco saponificado microemulsionados na inibição da corrosão de aço carbono

The effectiveness of microemulsions (ME) of saponified coconut oil (OCS-ME) and diphenylcarbazide (DC-ME) on a carbon steel corrosion inhibition process was evaluated using an electrochemical method of polarization resistance. The ME was prepared with OCS, butanol, kerosene and saline solutions. OCS-ME and DC-ME showed highest inhibitions effects (77% and 92%, respectively) at lower concentrations (0.5% and 0.48 - 0.50%, respectively). The surfactant OCS (in H2O) showed lower efficiency (63% at 0.20 - 0.25% concentration). The greatest inhibitory effect of DC-ME could be correlated with the chemical structure and the rich O/W ME system, which are very important for adsorption phenomena in interfacial ME systems.

Especiação redox de cromo em solo acidentalmente contaminado com solução sulfocrômica

Determination of Cr(VI) and Cr(III) was studied in soil samples accidentally contaminated with sulphochromic solution. Molecular absorption spectrophotometry based on the diphenylcarbazide method was used for the determination of Cr(VI) after its alkaline extraction. The total chromium concentration was determined using ICP OES. The quantification of Cr(III) was accomplished by subtracting the Cr(VI) concentration from the total chromium concentration. Regardless of the known contamination of the soil samples by sulphochromic solution, concentrations of Cr(VI) were below the detection limit. Addition and recovery experiments for Cr(VI) in soil samples with and without organic matter indicated its influence on the reduction of Cr(VI) to Cr(III).

Especiação de cromo em cimentos e derivados de cimento brasileiros

A method for determination of Cr(III) and Cr(VI) in cement and cement-related materials was studied. Molecular absorption spectrophotometry based on 1,5-diphenylcarbazide as chromogenic reagent was used for determination of Cr(VI) after alkaline extraction. The total chromium concentration was determined using flame atomic absorption spectrometry (FAAS) after complete sample decomposition by fusion. The quantification of Cr(III) was accomplished by subtracting the Cr(VI) concentration from the total chromium concentration. The concentration of Cr(III) in the samples ranged from 10.9 to 88.0 mg kg-1, whereas only in few samples the Cr(VI) concentration was higher than the value established by the European Community to this type of sample [2 mg kg-1 Cr(VI)].

Ácido myrsinoico a e derivado: inibidores da fotossíntese in vitro

Myrsinoic A acid, isolated from Myrsine cuneifolia and its hydrogenated derivative had their effect on photosynthesis tested. The compounds inhibited the electron flow (basal, phosphorylating and uncoupled) from water to methylviologen; therefore, they act as Hill reaction inhibitors in spinach thylakoids. They inhibited partial reactions of PSII electron flow from water to 2,5-dichloro-1,4-benzoquinone, from water to sodium silicomolybdate, and partially electron flow from diphenylcarbazide to 2,6-dichloroindophenol. Their inhibition sites were at the donor and acceptor sides of PSII, between P680 and Q A. Chlorophyll a fluorescence measurements confirmed the behavior of the compounds (pool of quinones).