Structural study of PLGA [copoly (DL-lactic/glycolic acid)], a biodegradable polymer for parenteral sustained release preparations, by tandem mass spectrometry.

A copoly (DL-lactic/glycolic acid) (PLGA), with a weight-average molecular weight of about 8400, has been characterized using fast atom bombardment (FAB)-tandem mass spectrometry in order to determine the sequence. Because of the large molecular size, PLGA was partially hydrolyzed and the terminal hydroxyl groups in the resulting oligomer mixture acetylated as the indicator. The FAB spectrum of this sample showed a complex ion signal pattern containing monomer to octamer. Diagnostic product ions containing useful information for sequence determination were observed in collision-induced dissociation-MS/MS and MS/MS/MS of these oligomer ions. The results of analysis for dimers through pentamers showed that they have random sequences of lactic and glycolic acid, suggesting that the whole structure of PLGA also has a random sequence.