Could Infrared Spectroscopy Identify Melamine‐Related Stone Using Melamine‐Contained Mixture as A Reference?

BACKGROUND: Recently, a method of infrared spectroscopy analysis to identify melamine-contained stone was established by examining melamine powders mixed with true urinary stones. However, several studies demonstrated melamine could be interacted with cyanuric acid or uric acid in water through hydrogen bonds. It presents a hypothesis that the infrared spectrum of melamine-contained stone formed in urine is probably different from melamine-contained dry mixtures. This study is to testify is it true. METHODS: The melamine-related mixtures were, respectively, prepared by mixing powders of melamine with cyanuric acid or uric acid in equimolar ratio. The melamine-related precipitates mimicking its related stone formation were, respectively, prepared by mixing melamine with cyanuric acid or uric acid in water at the given conditions. Subsequently, the melamine-related mixtures and precipitates were analyzed by infrared spectroscopy. RESULTS: The wave-number positions of powder mixtures of melamine-cyanuric acid and melamine-uric acid were a combination of these of their individual ingredients. The typical wave-number positions of melamine were showed in two melamine-contained mixtures. In contrast, these positions were disappeared or shifted greatly in the two melamine-related precipitates. In total, the spectrum of precipitates of melamine with cyanuric acid and uric acid had significantly differences with their powder mixtures. CONCLUSIONS: Our results indicate the identification of melamine-related stone by infrared spectroscopy could not use the infrared spectrum of melamine-contained mixtures as a reference.