this is regarding nitrate determination by 4500-NO3 B. Ultraviolet Spectrophotometric Screening Method. when the organic matter content is high, can we use an Allum solution to precipitate the organic matter (we have a wastewater sample which contaminated with tannin. this is from coir industry) once we add allum, colour and turbidity can be removed. so can we use the above method to determine the nitrate content?