Published: Journal of Analytical Toxicology, ISSN 0146-4760, Volume 31, Number 6, July/August, pp.342-346

Quantitative Endogenous Formate Analysis in Plasma Using Headspace Gas Chromatography Without a Headspace Analyzer
AbdulRazaq Sokoro[1], Denis Lehotay[1], and Jeff Eichhorst[1], Ronald Treble[2]
[1] Toxicology, Saskatchewan Disease Control Laboratory, 3211 Albert Street, Regina, Saskatchewan, S4S 5W6, Canada
[2]Chemistry/Biochemistry, University of Regina, Regina, Saskatchewan, Canada

The objective was to develop a simple routine method for quantitative measurement of endogenous formic acid in plasma and whole blood using headspace gas chromatography–flame ionization detection. (GC–FID). Two-hundred microliters of sample was placed in a 1-mL glass vial. Fifty microliters of aqueous ethanol (10%) was added as an internal standard and a derivatizing agent. Ethylformate formation was enhanced by addition of 200 µL concentrated sulfuric acid as a catalyst. The vials were then sealed immediately and placed in a water bath for 15 min at 60°C. One milliliter of this headspace gas was siphoned using a gas-tight syringe and injected into a GC–FID fitted with a capillary column. Ethanol eluted at approximately 3.0 min, and ethylformate eluted around 4.7 min. The limit of quantitation for ethylformate was 0.026 mmol/L, and the limit of detection was 0.020 mmol/L. Imprecisions for spiked plasma samples at 0.25 and 1 mmol/L were 10% and 9%, respectively, and recoveries were at 100% and 108%, respectively. A simple, reliable, and highly specific headspace analysis method for quantifying endogenous formate without the use of a headspace analyzer was developed. This method enables the routine clinical analysis of formate in plasma and whole blood samples.

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