Chromatography of ureas thioureas and related mammalian metabolites

The literature is abundant with examples of the remarkable versatility of chromatography for the detection and separation of a wide variety of ureas and thioureas. Thin-layer chromatography with its inherent simplicity of operation, rapidity, high degree of sensitivity and resolution (and utility for “pre-cleanup” prior to gas chromatographic analysis) is rapidly replacing paper chromatography. Gas chromatography is becoming more useful as a method for analyzing residues of compounds of pharmaceutical and agricultural interest in plants, soils and animal tissues and fluids. Its ability for the simultaneous determination of several components, such as isomers, homologs and metabolites during a single operation has been amply demonstrated. The utility of gas chromatography will increase with the possibility of decreasing the thermal instability of ureas by the preparation of suitable derivatives such as trimethylsilyl¹²¹, or possibly acetyl derivatives¹⁹³ (successfully utilized for pesticidal carbamates). The desirability of a satisfactory selective system for nitrogen as suggested by Coulson¹⁹⁴ as well as the use of pyrolytic techniques^195,196 (utilized in combination with gas chromatography for the analysis of barbiturates) appears to offer enhanced prospects for the greater utility of gas chromatography to urea and thiourea analysis.