Photometric extraction method for determination of cefalotin

A selective, accurate and precise photometric method for the determination of cefalotin (1) is proposed. The method is based on a preliminary hydrolysis of the antibiotic in a strong sulphuric acid medium at 100 degrees C for 15 min. The 2-thienylacetic acid (2) formed as degradation product is determined photometrically with ninhydrin in strongly acidic solution. In these conditions 2 forms a yellow reaction product, which is extracted with chloroform and the absorbance measured at 423 nm. The reaction is practically specific as none of the initial substances used in the preparation of cefalotin or of its degradation products (except 2) reacts with ninhydrin under these conditions. The only other antibiotic which also gives a coloured product with ninhydrin in this strongly acidic medium is cefalexin. The latter however does not interfere at its coloured product absorbs at 520 nm. The method is simple, fast and with sufficient accuracy and precision (coefficient of variation 0,57--0,88% and relative error 0,41--0,64%).