Direct injection of untreated serum using nonionic and ionic micellar liquid chromatography for determination of drugs.

The chromatographic behaviour of nonionic micelles used as the mobile phase in liquid chromatography is similar to that of anionic and cationic micellar mobile phases, with reversal of retention order as the micelle concentration is varied. This behaviour follows the prediction of the model developed for anionic surfactants. Nonionic micelle chromatographic interactions are simplified by reducing the extent of electrostatic interactions with the solute and, as a result, their retention dependencies more closely follow the mathematical predictions. Drugs in blood serum samples are quantitatively determined by direct injection of the serum onto the chromatographic column, with no column clogging or pressure build-up. The results are similar to those found with anionic micellar mobile phases, but are in contrast to the protein precipitation observed with cationic micelles. Solute-micelle equilibrium constants and the critical micelle concentration of Brij-35, determined chromatographically, are reported. The potential usefulness of nonionic micelles for the determination of theophylline, paracetamol, phenobarbital, carbamazepine, quinine, quinidine, morphine, codeine and cocaine is demonstrated.