Advances in chromatography for clinical drug analysis: supercritical fluid chromatography, capillary electrophoresis,...

Advances have been made in chromatography complement immunoassay for clinical drug analysis. Chromatographic theory shows that the minimum detectable mass is directly proportional to the square of column radius. Small internal diameter columns are capable of analyzing lower analyte concentrations, and high resolution is achievable in open capillary columns, concomitant with greatly reduced mobile phase consumption and waste. This review, based on the author's experience and literature, focuses on supercritical fluid chromatography (SFC), capillary electrophoresis (CE), and selected high-performance liquid chromatography (HPLC) methodologies--microbore and direct-sample analysis (DSA) using commercially available Restricted Access Media (RAM) and REMEDi. In investigating the feasibility of SFC, the "normal-phase-like" selectivity of carbon dioxide was established, affecting the design of the extraction protocol and the elution order of drugs and metabolites. For example, the "more polar" tautomer eluted after FK-506, opposite to the order in the reversed-phase HPLC analysis. CE was investigated by Shihabi et al. for the analysis of pentobarbital and iohexol, while Evenson and Wiktorowicz performed preliminary evaluation of several therapeutic drug monitoring (TDM) drug groups. Innovation in HPLC column technology and hardware have greatly enhanced clinical drug analysis. Microbore column, offering enhanced mass sensitivity and high resolution, utilizes small sample size of 5 microliters of serum for the analysis of chloramphenicol. Commercially available RAM include internal surface reversed phase, shielded hydrophobic phase, and dual zone media, readily applicable for serum drug analysis without any sample preparation. Recently, an automated HPLC REMEDi offers urine and serum drug screening for toxicology.