Evaluation of trace analyte identification in complex matrices by low-resolution gas chromatography – Mass spectrometry through signal simulation

• The distribution of abundance ratio of mass spectrum fragments can be asymmetric.
• A spreadsheet for the definition of abundance ratio acceptance criterion is presented.
• A signal noise model is used to estimate the false positive results rate.
• Bayes' theorem is used to combine the uncertainty of independent evidences.
• The methodology was applied to the identification of pesticide residues in foodstuffs.

The identification of trace levels of compounds in complex matrices by conventional low-resolution gas chromatography hyphenated with mass spectrometry is based in the comparison of retention times and abundance ratios of characteristic mass spectrum fragments of analyte peaks from calibrators with sample peaks. Statistically sound criteria for the comparison of these parameters were developed based on the normal distribution of retention times and the simulation of possible non-normal distribution of correlated abundances ratios. The confidence level used to set the statistical maximum and minimum limits of parameters defines the true positive rates of identifications. The false positive rate of identification was estimated from worst-case signal noise models. The estimated true and false positive identifications rate from one retention time and two correlated ratios of three fragments abundances were combined using simple Bayes' statistics to estimate the probability of compound identification being correct designated examination uncertainty. Models of the variation of examination uncertainty with analyte quantity allowed the estimation of the Limit of Examination as the lowest quantity that produced “Extremely strong” evidences of compound presence. User friendly MS-Excel files are made available to allow the easy application of developed approach in routine and research laboratories. The developed approach was successfully applied to the identification of chlorpyrifos-methyl and malathion in QuEChERS method extracts of vegetables with high water content for which the estimated Limit of Examination is 0.14 mg kg−1 and 0.23 mg kg−1 respectively.

Figure optionsDownload as PowerPoint slide