Profiling of organic acids by capillary gas chromatography–mass spectrometry after direct methylation in urine using trimethyloxonium tetrafluoroborate

Abstract

Trimethyloxonium tetrafluoroborate (TMO) is applied as derivatising reagent to transform urinary organic acids into their methyl esters. The method is suggested as an alternative to the use of diazomethane which is carcinogenic and explosive. In contrast to other methods avoiding diazomethane, such as derivatizations with acetyl chloride–methanol and boron trifluoride–methanol, which require an organic reaction medium and therefore an extraction of the organic acids from the urine, TMO efficiently reacts with the acids in an aqueous solution and can therefore be directly applied to native urine. The use of TMO simplifies and improves the sample preparation in the profile analysis of urinary organic acids by capillary GC–MS and hereby increases the speed of analysis. The method gives reproducible results which are comparable with the data obtained using conventional solid-phase extraction with strong anion-exchange cartridges prior to derivatisation.