Determination of substituted purines in body fluids by micellar electrokinetic capillary chromatography with direct sample injection.

Many substituted purines (theobromine, caffeine, paraxanthine, theophylline and uric acid, as well as other methylated xanthines and uric acids) can easily be separated and analysed in one run using micellar electrokinetic capillary chromatography with a boratephosphate buffer containing 75 mM sodium dodecyl sulphate (pH approximately 9). Serum, saliva and urine samples collected after the self-administration of caffeine and serum samples from patients receiving theophylline or caffeine pharmacotherapy were screened for substituted purines. The data presented show the ease of using on-column multi-wavelength detection for investigating the feasibility of direct sample application, the characterization of sample pretreatment procedures and peak confirmation by comparing absorption spectra. It is shown that the determination of purines in serum and saliva samples, including therapeutic concentrations of caffeine and theophylline, can be accomplished without any sample pretreatment, whereas sample extraction is required for the determination of purines in urine. Quantitative data for the determination of micromolar amounts of theophylline (samples from adult patients) and caffeine (samples from infants born prematurely) in serum samples compared well with data obtained by non-isotopic immunoassays. Micellar electrokinetic capillary chromatography with the direct injection of serum or saliva samples requires only microlitre volumes of sample and several different compounds can be determined within a few minutes.