YSI 9300 Photometer - Manual (Page 116)

Test Procedure - Correction Factor
If it is suspected that the sample contains orthophosphate, carry out the
following correction procedure. On the photometer, select the ‘Follow On’ option
on screen to continue the test program.
1 Fill a round glass test tube with diluted sample to the 10 ml mark.
2 Add one OP-AX tablet. Crush and mix to dissolve.
3 Add one OP-B tablet. Crush and mix to dissolve.
4 Stand for five minutes to allow full color development.
5 Take photometer reading in the usual manner.
6 The instrument displays the corrected organophosphonate concentration as
active PO
4
.
Interferences
Chloride in excess of 350 mg/l will cause low results for organophosphonate.
Samples containing chloride levels in excess of this value should be further
diluted prior to the start of the test.
Note
The results of this test are expressed in terms of mg/l (ppm) active phosphate
content. Commercially available products are normally sold as aqueous formulations
with a given active content. To utilise the test results, regard must be paid to the
active content of the product in use.
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