Characterization of (Methoxymethyl)melamine Resin by Combined Chromatographic/Mass Spectrometric Techniques

Three complementary techniques were applied to the characterization of a complex (methoxymethyl)melamine mixture: gradient reversed-phase liquid chromatography/mass spectrometry (LC/MS), size-exclusion chromatography/mass spectrometry (SEC/MS) and capillary zone electrophoresis/mass spectrometry (CZE/MS). The LC/MS system was used with an atmospheric-pressure chemical ionization interface and the spectra obtained showed characteristic fragmentation patterns and detailed structural information of the monomeric components: up to 18 individual monomeric and 7 dimeric components could be identified. The SEC/MS system was used with a (pneumatically-assisted) electrospray interface, thus providing soft ionization and molecular information about the trimers, the dimers, and the monomers, indicating that the total number of components exceeds one hundred. In addition, the applicability of CZE/MS and H/D-exchange CZE/MS was demonstrated using a tricoaxial sheath-flow electrospray interface. The CZE separation turned out to be governed by the number of unreacted melamine positions only. Detailed structural information could be deduced simply by combining the CZE migration behaviour, the mass spectrometry data and the total number of exchangeable hydrogen atoms as calculated from the H/D exchange experiments