Determination of optimum wavelength and derivative order in spectrophotometry for quantitation of hydroquinone in creams

UV derivative spectrophotometry was used for quantitative determination of hydroquinone in creams. The aim of this work was to investigate optimum wavelength and order of derivative, and to validate the proposed spectrophotometric method. The results of standard curves were calculated and statistically analyzed through the least squares method in the interval from 10.0 to 26.0 µg/mL, in the first, second, third and fourth order derivatives. The quantitative determination was carried out by using the zero-crossing (Z-C) and zero-peak (Z-P) methods. The proposed method is simple, of low cost and provides reliable results in order to be used in quality control of creams containing hydroquinone as active substance.

A espectrofotometria derivada no UV foi usada para a determinação quantitativa de hidroquinona em cremes. O objetivo desta pesquisa foi investigar o melhor comprimento de onda e a ordem da derivada, bem como validar o método proposto. Os resultados das curvas analíticas foram analisados estatisticamente pelo método dos mínimos quadrados no intervalo de 10,0 a 26,0 µg/mL, na primeira, segunda, terceira e quarta ordens da derivada. As determinações quantitativas foram realizadas utilizando os métodos "zero-crossing (Z-C)" e zero-pico (Z-P). O método proposto é simples, de baixo custo e fornece resultados confiáveis podendo ser usado no controle de qualidade de cremes contendo hidroquinona como substância ativa.

Determination of promethazine and its metabolite in urine by solid——phase extraction with celite and UV derivative spectrophotometry / 中国法医学杂志

Objective To establish a simple and rapid method for extraction and determination promethazine and its metabolite in urine.Methods The urine was added to celite column and the elutions was effected with dichloromethane.The eluat was evaporated on a water bath at 50℃.The dry residue was redissolved with 3.0ml H2SO4 solution of 0.05mol/L,and then zinc dust was added,in order to make it reaction on the water bath of 100℃ for 3min.The promethazine and its metabolite concentration were determined with the second derivative UV spectrum.Resvlts The extraction rate was 90% for both promethazine and its metabolite.The linear range of determination was 0.5～5.0?g/ml.Conclusion The method for determinating promethazine and its metabolite in urine is simple,convenience,and with high extraction rate.