Earlier this year, the serious illnesses and deaths of cats and dogs in the US was linked to the consumption of pet foods which had been manufactured with adulterated wheat glutens originating from China. Testing of the wheat glutens showed they contained significant levels of melamine and/or several related compounds including cyanuric acid, ammeline, and ammelide. These compounds are structurally similar, containing a 1,3,5-triazine ring (see figure). Quantitative analysis was needed as a partial basis for health hazard evaluations, to understand and track the sources of the problem, and to help assess cross contamination in the manufacturing chain. An HPLC-UV method was developed for the quantitative analysis of melamine, cyanuric acid, ammeline, and ammelide in adulterated grain proteins. The unique chemistry of this compound set presented some challenges in obtaining both resolution and adequate sensitivity. All four compounds possess acid-base functionalities, causing the predominant form of each compound (charged vs. uncharged) to be pH dependent, affecting both retention order and resolution. In addition, cyanuric acid, ammeline, and ammelide are all subject to a pH dependent keto-enol tautomerism. The UV spectra differ for the keto and enol forms, with generally much less sensitivity for the keto forms. In this approach, the four compounds were separated under reversed phase conditions using a phenyl-hexyl column at near neutral pH (pH 6.7 – 7.0). This pH range provided baseline resolution and good sensitivity for the four compounds, favoring the enol forms of the affected compounds. The method is suitable for determinations at levels above 0.1%w/w.