81-53
PHOSPHORUS, REACTIVE, continued
ACCURACY CHECK
Standard Additions Method
a) Snap the neck off a Phosphate Voluette Ampule Standard Solution,
50 mg/L PO
4
-
.
b) Use the TenSette Pipet to add 0.1 mL, 0.2 mL and 0.3 mL of standard,
respectively, to three 25-mL water sample. Mix each thoroughly. (For
AccuVac Ampuls use 50-mL Beakers.)
c) Analyze each sample as described above. The phosphate concentration
should increase 0.2 mg/L for each 0.1 mL of standard added.
d) If these increases do not occur, see Standard Additions (Section 1) for
more information.
INTERFERENCES
Large amounts of turbidity may cause inconsistent results in the
phosphate tests because the acid present in the powder pillow may
dissolve some of the suspended particles and because of variable
desorption of orthophosphate from the particles. For highly turbid or
colored samples, add the contents of one Phosphate Pretreatment
Powder Pillow to 25 mL of sample. Mix well. Use this solution to zero
the instrument.
The PhosVer 3 Reagent Powder Pillows should be stored in a cool, dry
environment.
The following may interfere when present in concentrations exceeding
these listed below:
Copper 10 mg/L
Iron 100 mg/L
Silica 50 mg/L
Silicate 10 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; see
Interferences, pH (Section 1).
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