Targeted mass spectral ratio analysis: A new tool for gas chromatography—mass spectrometry

An algorithm, referred to as targeted mass spectral ratio analysis (TMSRA) is presented whereby the ratios between intensities as a function of mass channel (m/z) of a target analyte mass spectrum are used to automatically determine which m/z are sufficiently pure to quantify the analyte in a sample gas chromatogram. The standard perfluorotributylamine (PFTBA) was used to evaluate the reproducibility of the collected mass spectra, which aided in selecting a mass spectral threshold for TMSRA application to a subsequent case study. Results with PFTBA suggested that a threshold of all m/z at or above 1% of the highest recorded m/z intensity should be included for targeted analysis. For the case study, 1-heptene was selected as the target analyte and n-heptane was selected as the interfering compound. These two compounds were chosen since their mass spectra are very similar. Chromatographic data containing a pure peak for these analytes were extracted, and mathematically added at various temporal offsets to generate various degrees of chromatographic resolution, Rs, for the purpose of evaluating algorithm performance, and indeed, TMSRA successfully quantified 1-heptene. At the higher Rs studied (0.6≤Rs≤1.5) a deviation within±1% and a RSD generally below 1% were achieved for 1-heptene quantification. As the Rs decreased, the deviation and RSD both increased. At a Rs=0, a deviation of ∼9% and a RSD of∼9% were achieved.