A SPME-GC/MS Procedure for the Determination of Fatty Acid Ethyl Esters in Hair for Confirmation of Abstinence Test Results

Fatty acid ethyl esters (FAEE), direct metabolites of ethanol, are suitable alcohol markers that can be detected in different tissues. The determination of FAEE in hair can help to evaluate social and excessive alcohol consumption. Due to the presence of FAEE in the hair of tee-totalers, proving alcohol abstinence seems to be impossible. To verify these results, an solid phase micro extraction-gas chromatography/mass spectrometry procedure for the determination of the four FAEE: ethyl myristate, ethyl palmitate, ethyl oleate and ethyl stearate in hair was validated with special focus on low concentration levels. Besides very high sensitivity (limits of detection between 0.005 and 0.009 ng/mg), good results for linearity, precision and accuracy, recovery and stability were achieved. In addition, 73 hair samples with measured ethyl glucuronide (EtG) concentrations between 4 and 10 pg/mg were analyzed for FAEE. By using the following cut-offs: EtG: 7 pg/mg, FAEE: 0.2 ng/mg a satisfying matching rate of 72.6% was found. This shows that FAEE can be determined to verify borderline EtG concentrations even in the context of abstinence tests. However, the diversified influencing factors on analyte concentrations in hair, which may explain the large deviations between EtG and FAEE results observed in some cases, have to be mentioned when interpret ambiguous results.