Liquid chromatographic determination of 2-thioxothiazolidine-4-carboxylic acid isolated from urine by affinity chromatography on organomercurial agarose gel

Abstract

Urinary 2-thioxothiazolidine-4-carboxylic acid is a useful indicator to assess the degree of occupational exposure to carbon disulfide. A new procedure is described for the isolation of this compound from urine prior to reversed-phase high-performance liquid chromatography. It is based on liquid-liquid extraction with methyl tert-butyl ether, followed by affinity chromatography on organomercurial agarose gel. 5-Carboxythiouracil is used as internal standard. The superior selectivity of affinity chromatography for the isolation of 2-thioxothiazolidine-4-carboxylic acid from urine permits an isocratic high-performance liquid chromatographic analysis. The total recovery of 2.5 mg of 2-thioxothiazolidine-4-carboxylic acid/g of creatinine in spiked urine by liquid-liquid extraction combined with affinity chromatography was 48.0% (SD 2.0%, n = 8). Within-run and within-day relative standard deviations averaged 4.0% (means = 2.48 mg/g of urinary creatinine, n = 9) and 6.5% (means = 1.19 mg/g of urinary creatinine, n = 15), respectively. The detection limit of the method was estimated at 0.05 mg of 2-thioxothiazolidine-4-carboxylic acid/g of urinary creatinine. The identity and spectral purity of 2-thioxothiazolidine-4-carboxylic acid detected in the urine extracts were confirmed by diode-array UV-vis detection. Typical 2-thioxothiazolidine-4-carboxylic acid levels in individual workers exposed to carbon disulfide ranged from nondetectable to 11 mg/g of urinary creatinine, several of which exceeded the generally accepted biological exposure index of 5 mg/g of urinary creatinine.