Analysis of barbiturates in human serum and urine by high-performance capillary electrophoresis-micellar electrokinetic capillary chromatography with on-column multi-wavelength detection.

The analysis of barbiturates in human serum (or plasma) and urine by high-performance capillary electrophoresis-electrokinetic capillary chromatography with on-column fast-scanning multi-wavelength detection is discussed. The use of a buffer of ca. pH 8 and containing sodium dodecyl sulphate provides a medium suitable for fast and high-resolution separations of barbiturates. Seven barbiturates are characterized by their retention and absorption spectra between 195 and 320 nm. Comparison of these computer-stored data with those of unknown samples is shown to allow the identification of barbiturates in samples of patients undergoing pharmacotherapy and in toxicological urine and serum specimens. Three-dimensional electropherograms provide reliable information on the requirement and suitability of sample pretreatment procedures. With urine, extraction of barbiturates prior to analysis is necessary. With human serum several barbiturates, including phenobarbital, are shown to elute in an interference-free window in front of uric acid and the proteins, allowing these substances to be determined by direct sample injection. The need for multi-wavelength detection over a relatively wide wavelength range as a means of peak confirmation in electrokinetic capillary analyses is demonstrated and limitations of this technique for compounds with similar retention behaviour and absorption spectra are discussed.