UC Davis

Forensic alcohol analysis of ante-mortem blood samples is a common service performed in many laboratories across the country. 1-Propanol is a commonly used internal standard for the detection and quantification of ethanol in these samples. Ethanol-d6 could potentially be a more reliable internal standard due to sharing a similar structure and vapor pressure to ethanol and because it would also be similarly affected by outside factors as ethanol. However, ethanol-d6 is more expensive and its use may require adjusting the parameters of a gas chromatograph to achieve adequate separation from ethanol for quantitation by flame ionization detection (FID). In this study, aqueous ethanol samples were individually spiked with either 1-propanol or ethanol-d6 and run through a headspace GC-MS to quantify the concentration of ethanol present and to compare the results between the two internal standards. Samples drawn from 0.080 g/dL ethanol solutions of various sodium fluoride and potassium oxalate salt concentrations were also spiked with the internal standards, run, and compared to test the salting-out effect on the internal standards. This study found that while 1-propanol was more accurate than ethanol-d6 in the salt-free samples, ethanol-d6 was more accurate when salts were present. It also found that 1-propanol was more precise at lower ethanol concentrations while ethanol-d6 was more precise at higher concentrations. However, ethanol-d6 is over 300 times more expensive than 1-propanol on a cost per run basis, so this may outweigh any potential improvements in assay performance.