Charge-remote molecular hydrogen removal in protonated and alkali-cationized long-chain fatty acid esters upon cesium ion bombardment

The mass spectral behavior of cationized saturated fatty acid derivatives h as been studied in order to gain insight into the loss of molecular hydroge n during cesium ion bombardment. It is shown that molecular hydrogen and hy drogen radical loss occurs for protonated and alkali (Li+/Na+)-cationized f atty acid methyl esters as well as for protonated acylcarnitines and that m olecular hydrogen loss is dependent upon the acyl chain length. Investigati on of ion structures by collision-induced dissociation tandem mass spectrom etry indicates that in the case of alkali-cationization a hydrogen radical is lost from all positions of the saturated acyl chain, whereas in the case of protonated molecules a hydrogen radical is predominantly eliminated fro m the protonated ester group. For the primary reaction of the dehydrogenati on chemistry, an ion-beam-induced excitation of a cationized molecule is pr oposed, yielding a diradical species that gives rise to an intermolecular r eaction with a neutral analyte molecule. Subsequent cationization of the ne utral [M-H-2] species formed in this primary reaction leads to the formatio n of the satellite ion at mit values 2 u lower compared to the cationized m olecule. (Int J Mass Spectrom 188 (1999) 39-52) (C) 1999 Elsevier Science B .V.