The HI937521-01 are high quality reagents that are pre-measured, allowing for users to achieve fast and accurate colorimetric measurements. These reagents follow an adaptation of the oxalate method. The reaction between calcium and reagents causes a red tint in the sample. By adding the HI937521-01 reagents to the sample, a reaction will take place and a compatible photometer can be used to determine the concentration from the color that is produced. The results will be displayed in mg/L (ppm) as calcium. These reagents are designed to be used with samples that have an expected range of 0 to 400 mg/L calcium.