Phosphorus, Reactive
Phosphorus, Reactive
PhosphorusReac_PT_High_MOL_Eng_Ody.fm Page 5 of 6
Standard Solution Method
1. Use a 10.0-mg/L Phosphate Standard in place of the sample. Results should
be between 9.0 and 11.0 mg/L phosphate.
2. To adjust the calibration curve using the reading obtained with the 10-mg/L
PO
4
3–
Phosphate Standard Solution, touch Options on the current program
menu. Touch
Standard Adjust.
3. Touch
On. Touch Adjust to accept the displayed concentration (the value
depends on the selected chemical form). If an alternate concentration is used,
touch the number in the box to enter the actual concentration, then touch
OK.
Touch
Adjust.
For more information, see Section 3.2.4 Adjusting the Standard Curve on page 40.
Method Performance
Precision
Standard: 10.0 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
See Section 3.4.5 Sensitivity on page 44 for more information.
Summary of Method
In the molybdovanadate method, orthophosphate reacts with molybdate in an
acid medium to produce a phosphomolybdate complex. In the presence of
vanadium, yellow vanadomolybdophosphoric acid is formed. The intensity of
the yellow color is proportional to the phosphate concentration. Test results are
measured at 430 nm.
Program 95% Confidence Limits of Distribution
489 9.9–10.1 mg/L PO
4
3–
Portion of Curve ∆Abs ∆Concentration
0.0 ppm PO
4
3–
0.010 0.3 mg/L PO
4
3–
45.0 ppm PO
4
3–
0.010 0.4 mg/L PO
4
3–
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