The HI38061-100 are high quality reagents that are pre-measured, allowing for users to achieve fast and accurate phosphate measurements with the chemical test kit. These reagents follow the ascorbic acid method to determine phosphate concentration.

For determination of phosphate, the reagent containing ammonium molybdate and potassium antimonyl tartrate reacts in an acid medium with orthophosphate to form a phosphomolybdate complex. The phosphomolybdate complex is reduced by ascorbic acid, causing a blue colored complex to form; the greater the concentration, the deeper the color. A Checker Disc is included for an accurate, side-by-side, visual analysis to determine phosphate concentration. These reagents are designed to be used with samples in three ranges: 0.00 to 1.00 mg/L, 0.0 to 5.0 mg/L, and 0 to 50 mg/L PO₄^3-.