Midazolam in plasma from hospitalized patients as measured by gas-liquid chromatography with electron-capture detection.

The present assay was developed for quantifying midazolam in plasma of patients hospitalized in intensive-care units or undergoing anesthesia and receiving many other drugs as well. Plasma samples are alkalinized with NaOH and midazolam is extracted into n-hexane. The organic phase is evaporated and reconstituted in n-butyl acetate, and the midazolam is quantified by gas-liquid chromatography with electron-capture detection. The calibration graph for midazolam was linear in the ranges 5-200 and 200-800 micrograms/L. The CVs for precision and reproducibility of the assay were less than 8%. The method was very specific for midazolam; most of the drugs commonly used in anesthesia and in the intensive-care unit did not interfere with the assay. The lowest detectable concentration was 1 microgram/L. The method is adaptable for use with an automated chromatographic system.