Mass Spectrometry-Based Analytical Strategy for Comprehensive Molecular Characterization of Biodegradable Poly(lactic-co-glycolic Acid) Copolymers

Abstract

An analytical methodology with mass spectrometry as the core technique was developed for precise characterization of end groups, size, and comonomeric composition of poly(lactic-co-glycolic acid) (PLGA) copolymers, as a preliminary step to qualify their biodegradability. Four PLGA samples were studied, with GA molar content varying from 0 to 50% and M w ranging from 18 to 75 kg mol −1 according to the supplier. Size exclusion chromatography (SEC) and liquid state nuclear magnetic resonance (NMR) were used as either complementary or validation techniques. As confirmed by tandem mass spectrometry (MS/MS) experiments, macrocycles were most prominent in the low mass range. Nevertheless, elemental compositions derived from high resolution (HR) mass measurements of linear species were consistent with chain terminations revealed by NMR. Off-line coupling of SEC with matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) permitted calibration curves to be built based on absolute molecular weights and, although slightly overestimated, so-obtained M n and M w values compared well with SEC and NMR results. Homogeneity of the co-monomeric content of all chains within each PLGA sample was demonstrated using surface-assisted laser desorption/ionization in a reactive mode (reactive-SALDI), a newly developed technique that takes advantage of residual acid on desorption ionization using through-hole alumina membrane (DIUTHAME) chips to induce dissociation of highmolecular-weight polymers containing cleavable C−O bonds. All HRMS data were best handled with Kendrick analysis, which helped reveal minor species and allowed automated computation of congested mass spectra.

Reactive Desorption Electrospray Ionization Mass Spectrometry To Determine Intrinsic Degradability of Poly(lactic-co-glycolic acid) Chains

“…Most of soluble samples (with LA% of 50, 65, 75, or 100%) have been thoroughly characterized in a previous study. 9 Detailed analysis of the soluble PLAGA 85/15 as well as the low-solubility PLAGAs 5/95, 10/90, and 20/80 is reported in the Supporting Information (Figures S1−S6, and Tables S1 and S2). Methanol, water, and acetonitrile were HPLC-grade obtained from SDS (Peypin, France).…”

“…5 When performed on the whole sample, MALDI-MS determination of MWD was reported for PLA with M n below 20 kDa, 6−8 whereas the mass range could be extended up to M n 150 kDa for preparative fractions of PLAGA obtained after size exclusion chromatography (SEC). 9 The impact of end groups on the degradation process is minor because the hydrolysis of solid PLAGA in solution is known to occur via random scission of chains. 10 However, the presence of macrocycles in PLA or PLAGA samples may also modify crystalline properties and hence affect bulk degradability.…”

“…10 Surface-assisted laser/desorption ionization (SALDI) 21 performed in reactive mode was recently reported as an interesting alternative to the traditional 1 H NMR determination of comonomeric composition. 9 This method takes advantage of phosphoric acid present at trace levels in the membranes developed for desorption ionization using through-hole alumina membrane (DIUTHAME) 22 to promote, upon laser irradiation, proton-induced dissociation of high-molecular-weight polymers containing cleavable C−O bonds. 23 Reactive SALDI of PLAGA (with M n ranging from 10 to 25 kDa) was shown to generate a set of small co-oligomeric ions (with m/z < 350) that revealed the LA/GA composition of the original chains.…”

“…23 Reactive SALDI of PLAGA (with M n ranging from 10 to 25 kDa) was shown to generate a set of small co-oligomeric ions (with m/z < 350) that revealed the LA/GA composition of the original chains. 9 After degradation occurs, the decreasing size of hydrolysis products is measured as a function of time, so techniques favoring the detection of low mass species are preferred to (i) identify chain terminations that reveal solvolysis, (ii) determine their relative LA/GA content, and (iii) measure their average molecular weight. In this context, ESI is best suited for soft ionization of polar compounds expected after the degradation of PLA and PLAGA, as reported in studies that performed MS, 24−27 high-performance liquid chromatography−MS (HPLC−MS), 28,29 or MS/MS.…”

Mass Spectral Filtering by Mass-Remainder Analysis (MARA) at High Resolution and Its Application to Metabolite Profiling of Flavonoids

“…Besides the MDF process, the Kendrick Mass Defect (KMD) [19] and related methods [20][21][22] (Re-KMD) are applied for the analysis of complex mass spectra, however, it is not widespread in metabolomics.…”