Introduction¶

We have experimented with four different methods for measuring phosphate levels in water samples with the colorimeter. The first 3 methods listed below use the common ascorbic acid method (APHA Standard Method 4500-P E) and can be used to measure up to 30 ppm phosphate depending on the test you use. For high range phosphate levels, there is also the vanadate-molybdate method (APHA Standard Method 4500-P C).

1. Ascorbic acid method - Uses a number of reagents. Prepare fresh testing reagent each time.
2. Hach PhosVer3 reagent - Powdered reagent. Requires mixing and timing.
3. API test kit - 2 x bottles of liquid reagents. Requires measuring within 5-10 minutes of adding the last reagent.
4. Vanadate-molybdate method. Liquid reagent. Easy test but only for high-range phosphate.

Of these four methods, we have used the Hach PhosVer3 reagent the most. Although it does require a mixing step, the reagent is easy to use and we find the test has reproducible results so far.