81-39
PHOSPHORUS, TOTAL, continued
INTERFERENCES
Large amounts of turbidity may cause inconsistent results in the test
because the acid present in the powder pillows may dissolve some of the
suspended particles and because of variable desorption of
orthophosphate from the particles.
The PhosVer 3 Phosphate Reagent Powder Pillows should be stored in a
cool, dry environment.
The following may interfere when present in concentrations exceeding
these listed below:
Aluminum 200 mg/L
Chromium 100 mg/L
Copper 10 mg/L
Iron 100 mg/L
Nickel 300 mg/L
Silica 50 mg/L
Silicate 10 mg/L
Zinc 80 mg/L
Arsenate and hydrogen sulfide do interfere.
Highly buffered samples or extreme sample pH may exceed the
buffering capacity of the reagents and require sample pretreatment.
PRECISION
DR/700: In a single laboratory, using a standard solution of
4.20 mg/L PO
4
3-
and two lots of reagent with a DR/700, a single operator
obtained a standard deviation of ±0.11 mg/L PO
4
3-
.
SAMPLE DISPOSAL INFORMATION
The phosphate vials contain only materials that are non-regulated for
disposal. Neutralize the vial solutions to a pH of 6-9 and dispose of as a
normal non-regulated material.
SUMMARY OF METHOD
Orthophosphate reacts with molybdate in an acid medium to produce a
Phosphomolybdate complex. Ascorbic acid then reduces the complex,
giving an intense molybdenum blue color.
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