Structure elucidation of 2,4-dinitrophenylhydrazone derivatives of carbonyl compounds in ambient air by HPLC/MS and multiple MS/MS using atmospheric chemical ionization in the negative ion mode

Ion trap multiple fragmentation mass spectrometry (MSn) combined with high-performance liquid chromatography (HPLC) has been used for the structure elucidation and identification of 2,4-dinitrophenylhydrazone derivatives of carbonyl compounds' in ambient air samples, Atmospheric pressure chemical ionization in the negative ion mode was the most suitable detection method. Different measures are described to decrease the MS background originating from the HPLC system. Low-picogram quantities were detectable in extracted mass chromatograms generated from full-scan records. Fragment ions produced by MS/MS allowed identification of substructures of the carbonyls. Detailed fragmentation paths were studied by MS3 to MS4 using reference compounds. A fragmentation scheme was established which enabled a structure confirmation and identification with 1-10 ng by HPLC/MS/MS. The identification of a compound coeluting with n-pentanal-DNPH and of a dimerization byproduct are given as examples.