A method for the routine determination of chlorpropamide in plasma.

THE METHOD suggested here was developed to provide a rapid and simple yet reliable routine procedure for the determination of plasma concentrations of chiorpropamide (1-propyl-3-p-chlorobenzene sulfonylurea). It is based on the principle that sulfonyl ureas are degraded to an amine and presumably the corresponding sulfonamide when heated in an inert solvent under controlled conditions. The resulting amine reacts with added b-fluoro-2,4-dinitrobenzene to form a yellowish colored derivative which can be analyzed colorimetrically. The coupling of these two reactions in a single step was suggested by Spingler (1) in his report of a possible method for the colorimetric determination of tolbutamide (1-butyl-3-p-tolylsulfonylurea) in serum. Isoamyl acetate serves as an excellent extraction solvent for the removal of chlorpropamide from acidified plasma or serum. It appears to extract completely the compound under the conditions described in the procedure. In addition, it serves as a reaction solvent for the decomposition of the sulfonyl urea and the subsequent formation of the 2,4-dinitrophenyl derivative. n-Propyl amine is produced quantitatively from the breakdown of the chlorpropamide-at least, a proportionate amount is always produced at various concentrations as measured by this technique. The absorption spectra of the 2,4-dinitrophenyl derivative has a maximum at 346 m and a plateau at approximately 395 to 400 mp.. The extension value at 346 m is almost three times the value at 400 m ; how-