An HPLC method with UV detection, pH control, and reductive ascorbic acid for cyanuric acid analysis in water

Every year over 250 million pounds of cyanuric acid (CA) and chlorinated is ocyanurates are produced industrially. These compounds are standard ingredi ents in formulations for household bleaches, industrial cleansers, dishwash er compounds, general sanitizers, and chlorine stabilizers. The method deve loped for CA using highperformance liquid chromatography (HPLC) with UV det ection simplifies and optimizes certain parameters of previous methodologie s by effective pH control of the eluent (95% phosphate buffer: 5% methanol, v/v) to the narrow pH range of 7.2-7.4. UV detection was set at the optimu m wavelength of 213 nm where the cyanuric ion absorbs strongly. Analysis at the lower pH range of 6.8-7.1 proved inadequate due to CA keto-enol tautom erism, while at pHs of <6.8 there were substantial losses in analytical sen sitivity. In contrast, pHs of >7.4 proved more sensitive but their use was rejected because of CA elution at the chromatographic void volume and due t o chemical interferences. The complex equilibria of chlorinated isocyanurat es and associated species were suppressed by using reductive ascorbic acid to restrict the products to CA. UV, HPLC-W, and electrospray ionization mas s spectrometry techniques were combined to monitor the reactive chlorinated isocyanurates and to support the use of ascorbic acid. The resulting metho d is reproducible and measures CA in the 0.5-125 mg/L linear concentration range with a method detection limit of 0.05 mg/L in water.