The application of isotopically labeled analogues for the determination of small organic compounds by GC/MS with selected ion monitoring.

The study aimed to show the limitations and advantages of the use of stable isotope labeled internal standards (SILISs) for the quantification of small polar compounds (ibuprofen, diclofenac, metoprolol, bisphenol A, 17β-estradiol) in water samples by GC/MS with selected ion monitoring (SIM). The selection of SIM ions shows that for some of the analytes, in the form of trimethylsilylated derivatives, it is problematic to have a minimum of two qualifiers because of the poor mass spectra, high impact of the background or overlapping of the peaks from the analytes and SILISs. The "isotope effect" was observed on GC chromatograms. During the development of the SIM method, special attention was given to the qualifier/quantifier ratio, for which a variety of acceptance criteria can be found in the official guidelines. The values of the solid-phase extraction efficiency, as well as the matrix effect and absolute recovery were the same for the analytes and their corresponding SILISs. The developed method was used for the quantification of analytes in wastewaters.