Evaluation of the variation in relative response factors of GC-MS analysis with the internal standard methods: Application for the alcoholic products quality control

Abstract

This paper focuses on the evaluation of variation of relative response factors (RRFs) obtained by two internal standard (IS) methods that are used to control the quality of alcoholic products. A standard IS method using 1-pentanol was compared with an "Ethanol as IS" method. The variation of RRF values for both methods was determined using standard solutions based on 20, 40 and 96% ethanol-water matrices. For this purpose, solutions of the ten most abundant volatile compounds were analysed at four different concentrations (250, 500, 1000 and 5000 mg L^-1 absolute alcohol, AA) within these matrices. Each solution was measured four times by gas chromatography-mass spectrometry (GC-MS) in single ion monitoring (SIM) mode under repeatability conditions. Our results showed that for the 40% and 96% matrices, the ethanol and standard IS methods showed similar relative standard deviations (RSDs) variation of no more than 2% within the 250-1000 mg L^-1 AA volatile compounds concentration range. For the 20% matrix as well as for the 250-5000 mg L^-1 AA concentration range the resulting variation in calibration factors reaches 10% for both methods. As for the whole range of 20-96% alcohol by volume (ABV) and 250-5000 mg L^-1 AA volatile concentration range, the resultant RRFs for the standard IS method (8% RSD) were more stable than those for the ethanol IS method (almost 40% RSD). Nonlinearity of the signal-to-amount dependence was also assessed with respect to the injection and detection processes.

Keywords: Alcoholic products; Calibration; Ethanol as IS; GC-MS; Internal standard method; Quality control; Relative response factors.