Effect of nitro groups and alkyl chain length on the negative ion tandem mass spectra of alkyl 3-hydroxy-5-(4 '-nitrophenoxy) and alkyl 3-hydroxy-5-(2 ', 4 '-dinitrophenoxy) benzoates

Tandem mass spectrometric behaviour was studied for a small combinatorial l ibrary of alkyl 3-hydroxy-5-(4'-nitrophenoxy) benzoates (A1-A5) and alkyl 3 -hydroxy-5-(2', 4-dinitrophenoxy) benzoates (B1-B5), The spectra were recor ded by negative ion electrospray low-energy collision induced dissociation (CID) tandem mass spectrometry, The product ion spectra of [M - H](-) of th e benzoates A1-A5 are similar, as are those of benzoates B1-B5, However, th e spectra of the B series compounds differ significantly from those of the A series owing to the second electron-withdrawing nitro substituent in the B compounds. In addition, the length of the alkyl chain has an effect on th e fragmentation. However, both series of compounds exhibit an abundant nitr ophenoxy ion formed by the loss of 3-hydroxybenzoate, This is at m/z 138 in A1-A5 and at m/z 183 in B1-B5, A precursor ion scan of the nitrophenoxy io n provides a rapid method to identify the synthesised compounds in this typ e of combinatorial mixture. Copyright (C) 1999 John Wiley & Sons, Ltd.