52-112
PHOSPHORUS REACTIVE, continued
When phosphate is determined in waters containing high salt levels, low
results may occur. To eliminate this interference, dilute the sample until
two successive dilutions yield approximately the same results.
As the concentration of phosphate increases, the color changes from
blue to green, then to yellow and finally to brown. The brown color may
suggest a concentration as high as 100,000 mg/L PO
4
3-
. If a color other
than blue is formed, dilute the sample and retest.
Highly buffered samples or extreme sample pH may exceed the
buffering capacity of the reagents and require sample pretreatment; see
Interferences, pH (Section 1).
SUMMARY OF METHOD
In a highly acidic solution, ammonium molybdate reacts with
orthophosphate to form molybdophosphoric acid. This complex is then
reduced by the amino acid reagent to yield an intensely colored
molybdenum blue compound.
REQUIRED REAGENTS
Cat. No.
High Range Reactive Phosphorus Reagent Set (100 Test) . . . . 22441-00
Include: (1) 1934-32, (1) 2236-32
Quantity
Description Per Test Units Cat. No.
Amino Acid Reagent . . . . . . . 1 mL . . . . . . 100 mL MDB*. . . 1934-32
Molybdate Reagent . . . . . . . . 1 mL . . . . . . 100 mL MDB* . . 2236-32
REQUIRED APPARATUS
Cylinder, 25 mL,
graduated mixing . . . . . . . . 1 . . . . . . . . .each . . . . . . . . . . 1896-40
DR/700 Filter Module
Number 52.01. . . . . . . . . . . 1 . . . . . . . . . each . . . . . . . . . . 46252-00
OPTIONAL REAGENTS
Amino Acid Reagent Powder Pillow . . . . . . 100/pkg . . . . . . . . . 804-99
Hydrochloric Acid Solution, 1:1 (6 N) . . . . . 500 mL . . . . . . . . . 884-49
Mercuric Chloride Solution . . . . . . . . . . . . . 100 mL . . . . . . . 14994-42
Phosphate Standard
Solution, 50 mg/L PO
4
3-
. . . . . . . . . . . . . . 599 mL . . . . . . . . . 171-49
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