Assessing analytical specificity in quantitative analysis using tandem mass spectrometry

Objectives: The necessity of confirmation of compound identity in quantitative analysis is well recognized for methods utilizing single mass spectrometry detection but is not commonly addressed for applications utilizing multiple-stage mass spectrometry (MSn). For MSn detection, no commonly accepted rules for assessment of analytical specificity in quantitative analyses have been established to date. Methods: To assure compound identity, we evaluated approaches based on monitoring multiple mass transitions of a target compound followed by comparison of the branching ratios of the mass transitions. Results: Monitoring multiple mass transitions along with evaluation of the ratio of their relative intensities allows the analyst to distinguish the target analyte from interferences in quantitative analysis. The strategy and the acceptance criteria are compound and method specific and should be established during the method development and validation. Conclusions: The certainty of analyte identity is very important in quantitative analysis using MSn detection; methods to verify analyte identity should be used in all critical applications.