A Direct Titrimetric Method for the Determination of Some Organic Bases in Pharmaceutical Preparations

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Abstract
A rapid titrimetric method using an extractive end-point has been developed for the determination of atropine, codeine, methadone and pethidine in pharmaceutical preparations. Chloroform is added to the organic base dissolved in pH 2·8 buffer solution so that the ratio of chloroform to aqueous phase lies between 2 to 1 and 4 to 1. Titration is carried out with sodium dioctylsulphosuccinate using Dimethyl Yellow screened with Oracet Blue B as indicator; at the end-point the chloroform phase changes colour from green to pink. The method is accurate to ± 1 per cent and has been applied to a number of injection, eye-drop, syrup and tablet preparations. Since little sample-preparation is required, most preparations may be assayed within 10 min., whilst the codeine content of complex compound tablets can be determined in 20 min.