Determination of free melamine content in uncured non-ionic and sulfonated melamine-based resins by reversed-phase and mixed-mode liquid chromatography

Melamine-formaldehyde resins are used in various industrial applications. As melamine is a toxic compound on the candidate list of Substances of Very High Concern, its content in melamine-based resins is important. Here we present two high-performance liquid chromatography methods suitable for the determination of free melamine content in uncured non-ionic and negatively charged melamine-based resins. A gradient reversed-phase liquid chromatography method using a C18 column was developed for the determination of free melamine content in non-ionic resins, while an isocratic mixed-mode liquid chromatography method using a Primesep 100 column was developed for the quantification of free melamine in sulfonated melamine-based resins. Both methods utilise ultraviolet detection, which allows the quantification of melamine in melamine-based resins with a limit of quantification of ∼10^-3% by weight and good repeatability and linearity over a wide range of melamine concentrations.