PITFALLS IN SELECTED ION MONITORING IN GAS-CHROMATOGRAPHY MASS-SPECTROMETRY - A THEORETICAL EXAMPLE

For the routine determination of residues of growth promoters two important types of low-resolution gas chromatograph-mass spectrometer may be distinguished: the ultra-trace full-scan instrument [e.g., the ion trap mass spectrometer (ITS40)] and most other quadrupole apparatus using the selected ion monitoring (SIM) mode for detecting very small amounts ( < 1-10 ng). In analysing biological extracts interference between matrix components, present at high concentrations, and analytes, present at low concentrations, should be avoided. In this investigation theoretical examples of pitfalls in SIM due to isotope interference (C-13) from matrix components with the analyte were considered. These interferences may lead to false-positive and -negative results and false quantification.