nIsoPair RCS
When a carbon-containing compound is analyzed using mass spectrometry, the instrument will detect both the 12C and 13C isotopologue signatures of the carbon-containing compounds. As a result, the number of scans with confirmed 12C/13C isotopologue pairs within a chromatography peak (nIsoPair) can be used to assess the peak quality and to ensure that the carbon-containing compounds are being analyzed.
nIsoPair is metric suggested by IDSL.IPA to assess the quality of chromatographic peaks in peak-picking analysis. The value of nIsoPair represents the number of detected scans within a peak with the expected isotopic ratio of a carbon-containing compound. Greater nIsoPair values indicate that there is greater confidence that the peak corresponds to a carbon-containing compound and that the chromatographic separation is of higher quality. Therefore, nIsoPair is an important factor in the IDSL.IPA workflow to distinguish "true" peaks from those that may be due to noise or other factors.
RCS (Ratio of Chromatogram Scan) is a metric that uses the nIsoPair value to further evaluate the quality of chromatographic peaks detected by IDSL.IPA. nIsoPair represents only the number of 12C/13C isotopologue pairs detected for a chromatographic peak which can be influenced by the size of the peak. To overcome this limitation, RCS normalizes the nIsoPair value by calculating the ratio of IsoPair scans above the top 80% of the peak height relative to the total number of chromatogram scans above the top 80% of the peak height. RCS can provide a quantitative measure of peak quality that takes into account the size of the peak. Overall, RCS provides a more robust metric to evaluate peak quality than nIsoPair alone.