The colorimetric estimation of 3-chlorpromazine in biological fluids.

With the increasing clinical use of chlorpromazine (" largactil ") it was found desirable to obtain a satisfactory method for its determination in biological fluids. Procedures have been described for this substance or for closely related phenothiazine compounds using plant peroxidases (Solsona and Mora, 1951), ferric chloride (Fossoul, 1950), sodium persulphate (Fossoul, 1951), picric acid (Uyeo and Oishi, 1952), sodium nitrate in concentrated hydrochloric acid (Berti and Cima, 1954), and concentrated sulphuric acid (Dubost and Pascal, 1953). Many of these depend on the red colours produced by the controlled oxidation of phenothiazine derivatives. Some of the methods examined proved insensitive to the small amounts of chlorpromazine likely to be found in biological material or they employed unstable reagents. The sulphuric acid method was both sensitive and employed a stable reagent. but difficulties have been encountered (Dubost and Pascal, 1955) with some batches of sulphuric acid due to fading of the colour. This can be overcome by the addition of traces of reducing agents to the sulphuric acid, but this