Determination of methenamine in biological samples by gas-liquid chromatography

Methenamine (hexamethylenetetramine), a urinary disinfectant, was determined in human plasma and urine by gas-liquid chromatography with a short (10 m) open-bore glass capillary column (split ratio 1:20) and nitrogen-selective detector. An almost quantitative recovery (92.1%) was achieved by simple dilution of water-containing samples (0.5 ml) with acetone (4.5 ml). After centrifugation an aliquot (2 microliter) of the supernatant was injected into the gas chromatograph. Selectivity and sensitivity of the nitrogen detector allowed the quantitation of unchanged methenamine in plasma and urine up to 24 h after a single therapeutic dose of 1 g. Reproducibility of the method was 7.6 and 2.1% (C.V.) in serum and urine, respectively. The time required for the analysis of one sample was approx. 2 min. Due to the simple extraction and short analysis time it was possible to analyze the samples concurrently with sample taking. Absorption of standard tablets and an enterosoluble preparation of methenamine hippurate was compared.