Phosphate Water Testing Method

Phosphate is found is any natural water source affected by plant, animal and industrial waste.

First Steps

Phosphate testing is done to find out just how well the water environment is coping. There are a number of ways to complete these tests, depending on where you are and your resources.

If you are not using a test kit, then the method is more complicated. You will need to fill a 50 milliliter graduated cylinder up to the 50 ml line with the water sample. Then pour this into a 125 ml Erlenmeyer flask. Add 1 ml of 36-percent sulfuric acid and swirl it around.

Then you will need a 0.05 gram spoon to add ammonium persulfate. Use only one spoonful and swirl it around until it is dissolved. Add some boiling stones before setting the flask on a hot plate. Gently boil this mixture for half an hour. Add deionized water during this time so that it will not boil dry. It will need to be between 10 and 50 ml at all times. At the end, allow it to boil down to 10 ml. Then remove the sample from the hot plate and let it cool.

Lab Testing

Add a drop of 1 percent phenolphthalein indicator into the cooled solution. While you are swirling this together, add sodium hydroxide with a pipette one drop at a time until it turns to a faint pink color. Then add 36-percent sulfuric acid drop by drop until this pink vanishes. Pour the solution into a 50 ml graduated cylinder and then rinse the flask with deionized water. You will need to add exactly 50 ml of this water to the cylinder and mix it thoroughly. Fill a test tube with 10 ml of the sample solution and drop in 1 ml of phosphate acid reagent. You will need to put a cap on this and mix it thoroughly.

Pour a 0.1 gram spoon of phosphate-reducing reagent. Put the cap on again and mix it until it has all been dissolved. Let it sit for five minutes. Take off the cap or stopper from the tube and put it in a phosphate comparator with an axial reader. You will need to match the color to the chart to find the result of the phosphate test and record it in ppm (parts per million) as the total phosphate level.

Test Kit

If you want to make it simpler, purchase a water phosphate test, which is complete with instructions. Make sure that the test tubes and all other instruments are clean before using.

Generally these tests include putting some water samples in the test tubes and testing with another chemical such as a molybdate agent to create a reaction that is explained on the chart provided. Use a spectrophotometer to gauge the colors.

About the Author

Jerry Garner has been writing semi-professionally for more than 15 years. The body of Garner's work includes informative articles, news and current events and historical essays. He is an avid sports fan and frequently writes about outdoor activities online.