Analysis and Migration of Hydrolyzate of Melamine-Formaldehyde Products by Liquid Chromatography-Mass Spectrometry

Melamine-formaldehyde (MF) tableware is popular in Chinese fast food restaurant and baby feeding. MF product could be hydrolyzed in hot-acid condition and release harmful components. So far, the studies on the hydrolysate and migration of MF products were mainly focused on formaldehyde, melamine and its hydroxy-derivatives. This study presented a deeper analysis for hydrolyzate of 17 MF samples using ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-QTOF MS). The samples were drilled to powder, then washed and hydrolyzed by diluted hydrochloric acid. An amide column was used for chromatographic separation with amino acetate solution-acetonitrile as mobile phase. Gradient elution was applied with aqueous phase varied from 10% to 30%. The detection was performed by electrospray ion source positive ion (ESI⁺) and information dependent acquisition (IDA) modes. SCIEX OS software was used for instrument control, data acquisition and processing, in which the “Analytical” module was used to complete the discovery of non-target peaks, and the “Explorer” module was used to achieve manual peak picking and rationality verifying of the deduced chemical structures. 61 components including melamine and 5 MF derivatives, 33 melamine-formaldehyde oligomers and their derivatives, 7 melamine analogues, 6 MF-polyethyleneglycol derivatives, 4 triethanolamine and related compounds, 4 polysacharides were discovered, while some of them were identified for the first time, such as methyl-melamine, methylol substituted methyl-melamine. The possible structure of the components were deduced by relative molecular mass, fragment ions and the synthetic principle of MF. MF derivatives and MF oligomers might generate M+H⁺ and M-H₂O+H⁺ quasi-molecular ion peaks, while M-H₂O+H⁺ peaks might get higher intensity. Characteristic fragments of melamine-formaldehyde oligomers and their derivatives were m/z 127.07, 139.07, 151.07, 163.07, 169.08, 181.08, 277.14, 289.14, etc. According to the literature, melamine might transform to ammeline, and then to ammelide. In this study, only ammeline was detected. Triethanolamine is an important additive in the synthesis procedure of MF resin to adjust the system acidity. MF-polyethyleneglycol derivatives might be produced from polyethyleneglycol (added for increasing toughness) and MF. 9 components including melamine, MF derivative, MF oligomer, 4 melamine analogues, triethanolamine and triethanolamine derivative were detected in migration solutions of 10 batches of MF tableware under two kinds of acid conditions. The intensity of the detected components was always higer under higher temperature migration condition. Specific migration limit of triethanolamine was 0.05 mg/kg for its hepatic and renal damage toxicity. Other migrated components were submitted to Pub Chem and AMBIT websites for toxicity retrieval and toxicity prediction. Limit toxicity information was found and no toxicity prediction could be deduced by Toxtee method. The research discovers abundant information in hydrolyzate of MF products and supports further toxicological studies and risk assessment.