Methyl methacrylate in poly(methyl methacrylate)--validation of direct injection gas chromatography

Gas chromatography (GC) was investigated for the determination of residual methyl methacrylate (MMA) in heat-processed poly(methyl methacrylate) (PMMA) denture base material emphasizing recovery and validation. Standard solutions of MMA and emulsion-polymerized PMMA in dichloromethane were analysed, before and after distillation by a room-temperature air stream into a liquid nitrogen trap, and in the presence of PMMA by direct injection. Quantitative NMR analysis using dimethyl sulphoxide as internal calibration standard in deuterated chloroform solutions provided validation. Good concordance was observed between results under all conditions; no problems arose from direct injection of PMMA solution for GC. Good straight line responses in log-log plots were generally observed. For GC and MMA: log-log calibration curve (slope: 0.9552 +/- 0.0051, r2: 0.9992, n = 32) indicated some non-linearity (t = 8.875, p approximately 4 x 10(-10)). Distillation gave slope: 0.9751 +/- 0.0213 (NS versus unity; t = 1.172, p > 0.25). For PMMA solutions, distillation (r2: 0.9301) gave greater scatter than direct injection (r2: 0.9704). For NMR: log-log plot of calculated versus actual MMA (slope: 0.9363 +/- 0.0157, r2: 0.9969, n = 13) again indicated non-linearity (t = 4.0682, p = 0.0019). PMMA solutions gave slope: 0.9477 +/- 0.0328, r2 = 0.9858 (NS versus unity; t = 1.5941, p = 0.13). Determination of MMA in PMMA by GC is recommended.