Phosphate yellow

The phosphate yellow method is a lab test used to measure the amount of phosphate (a form of phosphorus) in a water sample.

First, a water sample is collected and a special chemical mixture, called a reagent, is added. This reagent contains substances like ammonium molybdate and antimony, along with ascorbic acid. These chemicals react with the phosphate in the water and cause the sample to turn yellow.

The more phosphate there is, the stronger the yellow colour. A lab instrument called a spectrophotometer is used to measure exactly how yellow the sample is. This value tells scientists how much phosphate is present.