Photoinduced chemiluminescence of pharmaceuticals

A screening test for the forward development of chemiluminescence systems able to determine pharmaceutical compounds is reported. The test is based on the on-line photodegradation of the drugs by using a photoreactor consisting of 697 cmx0.5 mm PTFE tubing helically coiled around an 8 W low-pressure mercury lamp. Photodegraded pharmaceuticals are detected by direct chemiluminescence of the resulting photofragments and their subsequent reaction with potassium permanganate in sulphuric acid medium as oxidant. The screening comprised 97 compounds with different molecular structures and relevant members of the most important families of pharmaceuticals are tested (amino acids, carboxylic acids, nitrocompounds, phenyl-alkyl and aromatic amines, sulphonic acid amides, polycarbocyclics, monocyclic N-containing heterocyclics, bicyclic N-containing heterocyclics, tricyclic N-containing heterocyclics, N-S containing heterocyclics...). Due to the relevant influence of the medium for the photodegradation a wide range of pH's and buffer solutions were studied. The proposed strategy (photoinduced chemiluminescence, Ph-CL) allows the development of systems for the determination of many pharmaceuticals which do not present "native" chemiluminescence (e.g. chloramphenicol, dextromethorpham, riboflavin, ephedrine, piperazinamide, chlotrimazole, theophylline...). Moreover, Ph-CL allows to increase the sensitivity of chemiluminescence procedures based on direct chemiluminescence detection (e.g. sulphonamides, thiazides, nicontinamide, nortryptiline, levamisole, phenylbarbituric acid...).