Measuring total nitrogen, nitrate, and nitrite is critical for compliance with water safety standards. Previous methods for measuring total nitrogen were hazardous, time consuming, and expensive. Here we report a method for measuring total nitrogen in water and soil using alkaline persulfate digestion combined with a Nitrate Reductase assay. In this method the alkaline persulfate reaction oxidizes all nitrogen present in the sample to nitrate, Nitrate Reductase then is used to catalyze the reduction of nitrate to nitrite in the presence of NADH. The nitrite is then treated with Griess reagents to produce a pink color. The absorbance of this color is measured at 540 nm using a spectrophotometer and when compared to a standard curve of nitrate, treated with both the reduction and colorizing steps, can be used to determine the total nitrogen content of measured samples. This method customizes the measurement of total nitrogen by combining alkaline persulfate digestion with a Nitrate Reductase assay using enzyme based green chemistry. View Full Article