Hach DR/700 Procedures Manual page 13

Confirm
accuracy with
these steps
In addition, may
also be used to
troubleshoot a
test, improve
technique, check
reagents and to
assure cleanliness
of glassware
Levels of
common sample
substances or
conditions that
will cause
inaccurate
results
PHOSPHORUS, REACTIVE,
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 of the
DR/2000 Procedures manual or Water Analysis Handbook) 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
Iron
Silica
Silicate
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).
continued
10 mg/L
100 mg/L
50 mg/L
10 mg/L
81-53
xiii