A high-specificity aniline-based mass tag for aldehyde detection.

CAX-A can provide three levels of specificity for aldehyde detection. First is the known labeling specificity of the aniline functional group for aldehydes, which we confirmed here by observing a significant peak only from the aldehyde (S/N = 3388) when a mixture of an aldehyde, a ketone (no peak), and a quinone (S/N = 2.3) was tested. Second is the ease of formation of an analyte-characteristic first product ion (via anchimeric-assisted loss of triethylamine as a neutral) in MS2 from a CAX-labeled analyte. Third is the formation of a characteristic second product ion via loss of CO in MS3. CAX-A enables the specific, convenient detection of putative aldehydes in urine.