After poisonous melamine and cyanuric acid appeared in milk in China (Box 10-3) in 2008

Chapter 24, Problem 24-D

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After poisonous melamine and cyanuric acid appeared in milk in China (Box 10-3) in 2008, there was a flurry of activity to develop methods to measure these substances. An analytical method for milk is to treat 1 volume of milk with 9 volumes of H2O:CH3CN (20:80 vol/vol) to precipitate proteins. The mixture is centrifuged for 5 min to remove precipitate. The supernatant liquid is filtered through a 0.5-m filter and injected into a HILIC liquid chromatography column (TSKgel Amide-80 stationary phase) and products are measured by mass spectrometry with selected reaction monitoring (Section 21-4). Melamine is measured in positive ion mode with the transition m/z 127 n 85. Cyanuric acid is measured in negative ion mode with the transition m/z 128 n 42. (a) Write the formulas for the four ions and propose structures for all four ions. (b) Even though milk is a complex substance, only one clean peak is observed for melamine and one for cyanuric acid spiked into milk. Explain why