Reducing False Positives from Isotopic Misidentification in AS-MS
Enabling automated X–1 and X–2 isotopic misidentification filters in affinity selection-mass spectrometry (AS-MS) reduces false positive compound hits by 5% by preventing misassignment of isotopic peaks (e.g., M+1 or M+2) as distinct compounds, thereby improving hit list accuracy.
Reducing False Positives from Isotopic Misidentification in AS-MS
In affinity selection-mass spectrometry (AS-MS), one of the more challenging-to-discern causes of false positives is compound misidentification due to isotopic pattern overlap. These errors occur when the X+1 of one compound is perceived as the C12 of another compound. This can also happen at the X+2 level. This error is particularly perilous because it can affect both the original hit as well as the background hit.
Experimental
Scientists used Analytical Studio’s automated X–1 and X–2 cross-hit filter check during isotopic pattern matching to determine its impact on reducing false positives.
Key Finding
Enabling the automated X–1 and X–2 cross-hit filter check during isotopic pattern matching resulted in a 5% reduction in confirmed hits. This implies that 5% of the initial reported hits were likely false positives caused by isotopic confusion.
Example:
- The peak at m/z 338 was falsely identified as the C12 of the (M+Na)+ peak of the possible hit when it is actually the M+1 peak from the compound at m/z 337.
Impact:
- Without the X–1 and X–2 isotopic misidentification check, 1385 hits were reported.
- With the check enabled, hits dropped to 1315, a 5% reduction due to filtering false positives.
Recommended Practice
Always enable X–1 and X–2 misidentification checks during compound assignment. If your AS-MS data processing software doesn’t have this capability, consider looking for alternative tools. This simple processing setting can eliminate a significant portion of false positives at the source, improving the quality of your final hit list.
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