Thin-layer chromatographic determination of barbiturates and phenytoin in serum and blood

A method is described for the measurement of blood, serum and/or plasma levels of hexobarbital, phenobarbital, cyclobarbital and phenytoin by ultraviolet reflectance photometry on thin-layer chromatograms. The lowest concentrations measured were 0.3-0.7 mug/ml. The accuracy was similar to that of gas chromatographic procudures. For phenytoin determinations 5-(p-methylphenyl)-5-phenylhydantoin may be used as internal standard. The method has been applied to clinico-pharmacological assays, to the measurement of cyclobarbital elimination in man following a therapeutic dose, and to the study of phenobarbital kinetics in rats using serial blood samples.