An analytical method based on gas chromatography coupled to triple quadrupole tandem mass spectrometry (GC-MS/MS) was developed for the simultaneous determination of exogenous prohibited flavour compounds in coffee samples. In addition, gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) was developed to determine the origin of the founded prohibited flavour compound, N-methylpyrrole-2-carboxaldehyde (NMPCA). The good selectivity and sensitivity achieved in multiple reactions monitoring (MRM) mode allowed satisfactory confirmation and quantitation for the flavour compounds. The limits of detection (LODs) and limits of quantitation (LOQs) of these compounds were in the range of 0.0005-5.0 µg/kg and 0.002-16.0 µg/kg, respectively. The coffee samples were extracted with simultaneous distillation extraction (SDE) and NMPCA was analysed on a GC/C/IRMS system. The δ13C values of endogenous NMPCA in coffee beans were within a range of -35.0‰ to -31.1‰, whereas exogenous NMPCA was the range from -27.9‰ to -23.9‰. The validation results revealed that the GC-MS/MS method was sensitive and reliable, and the origin of NMPCA can be distinguished by GC/C/IRMS. Finally, this method was successfully applied to coffee samples analysis and NMPCA was found in coffee samples.
Keywords: Gas chromatography triple quadrupole tandem mass spectrometry; exogenous-prohibited flavour compounds; gas chromatography/combustion/isotope ratio mass spectrometry; multiple reactions monitoring.