Stable Isotope Dilution Assay Mass Spectrometry in Flavour Research: Internal Standard and Calibration Issues

Mass spectrometry is widely used in flavour research to quantify compounds by using isotopically labelled internal standards. However, equimolar amounts of different molecules do not give equal instrumental responses. Therefore, calibration of the mass spectrometer is needed prior to any sample quantification. If the mass of the internal standard differs from that of the analyte by more than 3 Da, the calibration curve is linear. If this mass difference is lower, a second-order curve is obtained that can be linearised by applying various mathematical treatments. We tested a number of linearisation techniques and recommend the method that uses isotopic enrichment calculation to control the quality of the mass spectrometer’s calibration.