A flow-injection conductimetric system procedure is proposed for the determination of paraoxon. The method is based on the inhibition of immobilized acetylcholinesterase in controlled porous glass beads (CPG) with acetylcholine as substrate. The enzymatic reaction is inhibited by a diethyl p-nitrophenylphosphate (paraoxon) solution. A 1,1'-trimethylene-bis(4-formylpyridinium bromide)dioxime solution was used to reactivate the enzyme. The correlation between the peak height, for a given acetylcholine concentration, is linear from 1.0X107 to 5.0X105 mol 1-' of paraoxon; therefore, the quantitative limit of detection was about I.OX 10-' mol 1-' of paraoxon. For semi-quantitative purposes, the limit can be considered to be about 1.0X10.8 moll'.The relative estimated standard deviation obtained using a l .OX 10.3 moll' acetylcholine solution and a 5.0X106 moll' paraoxon solution was 2.2% (n=8).
A possibilidade do uso do sistema de Análise por Injeção em Batelada (BIA) para a determinação potencimétrica de ácido acetilsalicílico em comprimidos, com eletrodo íon seletivo de membrana, foi investigado. Não há uma diferença significativa entre os resultados obtidos pelo método do proposto e pelo método padrão da Farmacopéia Britânica, ao nível de confiaça de 95%. Valores de 4% e 2.5% para o desvio padrão relativo foram obtidos pela aplicação do método BIA-potenciométrico e para as injeções respectivamente. Cerca de 90 determinações por hora podem ser realizadas pela aplicação do método descrito.The feasibility of the use of a Batch Injection Analysis (BIA) system for potentiometric determination of acetylsalicylic acid in tablets, with a membrane ion selective electrode, was investigated. There is no significant difference between the results obtained by the proposed method and those obtained by the Standard British Pharmacopaeia method 12 at the 95% confidence level. Values of 4% and 2.5% for R.S.D. were obtained by the application of the BIA-potentiometric method and for the injections respectively. About 90 determinations per hour can be performed with the proposed BIA potentiometric method.
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