Manual
PHOTOMETER TEST INSTRUCTIONS
__________________________________________________________________________________________
Phosphates are extensively used in detergent formulations and washing
powders. Phosphates also find widespread application in the food processing
industry and in industrial water treatment processes. Agricultural fertilizers
normally contain phosphate minerals and phosphates also arise from the
breakdown of plant materials and in animal wastes.
Phosphates can therefore enter water courses through a variety of routes -
particularly domestic and industrial effluents and run-off from agricultural land.
Phosphate is an important control test for natural and drinking waters.
Whilst phosphates are not generally considered harmful for human
consumption, they do exhibit a complex effect on the natural environment. In
particular phosphates are associated with eutrophication of water and with rapid
unwanted plant growth in rivers and lakes. Phosphates present in natural water
pass through into drinking water supplies.
The YSI Phosphate LR test provides a simple method of measuring phosphate
levels over the range 0 - 4 mg/l PO
4
. For drinking water the EEC has set a guide
level of 0.5 mg/l PO
4
(0.4 mg/l P
2
O
5
) and a maximum admissible concentration
of 6.7 mg/l PO
4
(5 mg/l P
2
O
5
).
Method
In the YSI Phosphate LR method, the phosphate reacts under acid conditions
with ammonium molybdate to form phospho-molybdic acid. This compound is
reduced by ascorbic acid to form the intensely colored ‘molybdenum blue’
complex. A catalyst is incorporated to ensure complete and rapid color develop-
ment, and an inhibitor is used to prevent interference from silica. The reagents
are provided in the form of two tablets for maximum convenience. The test is
simply carried out by adding one of each tablet to a sample of the water.
The intensity of the color produced in the test is proportional to the phosphate
concentration, and is measured using a YSI Photometer.
Photometer Method
AUTOMATIC
WAVELENGTH
SELECTION
0 – 4.0 mg/l PO
4
0 – 1.3 mg/l P
PHOT.28.AUTO