Ion Pairing

The ion pairing approach embedded in the IDSL.IPA allows to significantly decrease the number of candidate m/z for chromatography analysis and accelerate the workflow. The noise level prior to ion pairing is only applied to the most abundant ions in individual chromatogram scans. By default, IDSL.IPA screens for carbon-related isotopologues (ΔC = ¹³C - ¹²C = 1.003354835336 Da) since carbon-containing compounds are targeted almost in the entire mass spectrometry analyses.

Noted key advantages of the ¹²C/¹³C isotopologue pairing are

1. To reduce false positive peaks
2. To obviate the postprocessing ¹³C deisotoping step
3. To measure peak quality by number of scans with confirmed ¹²C/¹³C isotopologue pairs within a chromatography peak (nIsoPair)
4. To predict of number of carbons for elemental composition using the R¹³C = 1.0816C_n equation, where C_n indicates number of possible carbons, C_n <= 92
5. To evaluate the accuracy and specificity of a peak for an organic compound across multiple samples since the ratio of ions for a true positive should remain steadily constant

Ion pairing with satellite ions

IDSL.IPA is also able to screen for ion pairs with negative mass differences as shown below. This option allows to only focus on the ion pairs of interest and exclude non-related ions. Ratio of Satellite Ion (RSI) is calculated similar to R¹³C and may be used and adjusted using PARAM0025.