The HI93767A-50 are high quality reagents that are pre-measured, allowing for users to achieve fast and accurate colorimetric measurements. The method is an adaptation of the chromotropic acid method in which a digestion is required to convert all forms of nitrogen to nitrate. Sodium metabisulfite is added to remove potential interferences. The reaction between nitrate and the reagents causes a yellow tint in the sample. The intensity of color is determined by a compatible photometer and the concentration will be displayed in mg/L (ppm) as total nitrogen. These reagents are designed to be used with samples that have an expected range of 0.0 to 25.0 mg/L (ppm) nitrogen.