Ultra-high flow rate capillary liquid chromatography with mass spectrometric detection for the direct analysis of pharmaceuticals in plasma at sub-nanogram per millilitre concentrations

Ultra‐high flow rate liquid chromatography on large particle size stationary phases coupled with mass spectrometric detection (particularly tandem mass spectrometry, MS/MS) is gaining increasing usage for the direct determination of pharmaceuticals in biological fluids. The lack of sample preparation required prior to chromatographic and MS/MS analysis, together with the extremely high throughput of the chromatography, make the technique extremely attractive to the modern pharmaceutical bioanalyst. However, this lack of sample preparation also means that there is no potential for concentration of the sample and, as a consequence, the sensitivity of the technique has been limited. Liquid chromatography on the capillary scale offers sensitivity benefits compared with conventional liquid chromatography as the volume in which the analyte peaks are eluted is greatly reduced. In this paper, we present the use of ultra‐high flow rate liquid chromatography on the capillary scale. This enables the quantification of drugs in plasma at sub‐nanogram per millilitre concentrations from a very small (2.5 µL) aliquot of plasma without sample preparation. We also compare the resolution obtained by ultra‐high flow rate liquid chromatography with that achieved on short columns packed with conventional size packing materials operated in an isocratic manner. Copyright © 1999 John Wiley & Sons, Ltd.