Identification by headspace gas chromatography-mass spectrometry of in vitro degradation products of homo- and copolymers of l- and d, l-lactide and 1,5-dioxepan-2-one

Abstract

Poly( l-lactide) (PLLA), poly( d, l-lactide) (PDLLA), poly(1,5-dioxepan-2-one) (PDXO) and six different types of copolymers of l-LA-DXO and D,L-LA-DXO (80:20, 50:50 and 20:80) were hydrolysed in vitro in phosphate buffer (pH 7.4) at 37°C for periods of up to 20 months and the degradation products were identified by headspace gas chromatography-ion trap mass spectrometry. A suitable method to identify the decarboxylic acids and hydroxy acids formed was developed using derivatization with N- tert-butyldimethylsilyl-N-methyltrifluoroacetamide reagent. The derivatives gave a single Chromatographic peak with no tailing in the mass spectra. The main products identified in the in vitro buffers are lactic acid and 2-hydroxyethoxypropionic acid, which are the linear forms of the monomers d, l- or l-lactide and 1,5-dioxepan-2-one. The amount of degradation products formed depends on the copolymer composition and the degradation time.