Review of Drug Analysis with Direct Serum Injection on the HPLC Column

Abstract

Contrary to the expectations of the past decade, routine therapeutic drug monitoring by HPLC failed to expand. Although more extensive to perform, immunoassays have dominated the market for drug analysis in the last few years. This is attributed to the lengthy sample preparation needed for HPLC. However, HPLC remains the main method for therapeutic drug monitoring of the uncommon drugs and their metabolites. The method of direct serum injection on the column simplifies HPLC as an analytical technique and enables full automation. Advantages and disadvantages of this method of analysis are discussed. This review tries to summarize the different approaches for direct serum injection on the HPLC column: 1) Guard columns, 2) Micellar chromatography, 3) Internal surface reversed-phase chromatography, 4) Column switching, and 5) Wide-pore (protein) columns. With direct serum injection, the pH of the mobile phase is very critical for separating the drug of choice from the endogenous substances found in serum and for attaining good recovery, especially for drugs which are tightly bound to proteins. The percentage of the organic solvent in the mobile phase is another important factor in reducing serum protein precipitation at the column inlet. Generally, direct serum injection decreases column life on one hand but saves labor time and cost on the other hand. Both the scientific literature and the commercial column supplies emphasize the protection of the column rather than the simplification of the procedure. However, declining column prices, especially for cartridge columns, might encourage direct serum injection. Further applied research in this area is needed.