Hach DR2400 - Page 601

Phosphonates
Phosphonates
Phosphonates_PP_Other_PUV_Eng_Ody.fm Page 5 of 6
Accuracy Check
Ideally, a solution containing the phosphonate product being used should be
prepared. This will check the UV conversion of phosphonate to orthophosphate.
Alternatively, a phosphate standard can be used to check the accuracy or the
colorimetric part of the method.
Standard Solution
A 1-mg/L Phosphate Standard Solution (available from Hach) can be used to
check accuracy. Use 10 mL of this standard in place of the prepared sample in
step 9. Use deionized water for the blank. A multiplier value from Table 1 on
page 3 is not needed. The result should be 10.0 mg/L phosphate, due to a factor
of 10 in calibration.
Method Performance
Precision
Standard: 1.00 mg/L PO
4
3–
See Section 3.4.3 Precision on page 44 for more information, or if the standard
concentration did not fall within the specified range.
Sensitivity
The sensitivity depends on the sample volume.
Sensitivity is expressed as PO
4
3–
in this table. Use Tabl e 2 on page 3 to express as
a specific phosphonate.
See Section 3.4.5 Sensitivity on page 44 for more information.
Summary of Method
This method is directly applicable to boiler and cooling tower samples. The
procedure is based on a UV-catalyzed oxidation of phosphonate to
orthophosphate. The orthophosphate reacts with the molybdate in the PhosVer 3
reagent to form a mixed phosphate/molybdate complex. This complex is
reduced by the ascorbic acid in the PhosVer 3, yielding a blue color that is
proportional to the phosphonate present in the original sample. Test results are
measured at 880 nm.
Program 95% Confidence Limits of Distribution
501 0.97–1.03 mg/L PO
4
3–
Range (mg/L) Volume (mL) ∆Concentration
0–2.5 50 0.02 mg/L PO
4
3–
0–5 25 0.04 mg/L PO
4
3–
0–12.5 10 0.10 mg/L PO
4
3–
0–25 5 0.20 mg/L PO
4
3–
0–125 1 1.00 mg/L PO
4
3–