Ascorbic acid

The total phosphorus ascorbic acid method is a lab test used to measure all forms of phosphorus in a water sample.

First, the water sample is mixed with a strong acid and heated to break down any particles or organic matter, turning all phosphorus into a form called orthophosphate. After cooling, special reagents are added, including ascorbic acid (a form of vitamin C) and a colour-developing agent.

The sample turns blue if phosphorus is present. The darker the blue, the more phosphorus there is. A colour-measuring device called a spectrophotometer is used to read the exact amount of phosphorus.