Hach DR/850 - Page 389

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Analyze samples immediately for best results. If prompt analysis
is not possible, preserve samples by filtering immediately and
storing the sample at 4 °C (39 °F) for up to 48 hours.
Accuracy Check
Standard Additions Method
a) Snap the neck off a Phosphate PourRite Ampule Standard
Solution, 500 mg/L as PO
4
3-
.
b) Use the TenSette Pipet to add 0.1 mL, 0.2 mL and 0.3 mL
of standard, respectively, to three 25-mL samples. Mix
well.
c) Analyze each sample as described in the procedure. Each
0.1-mL addition of standard should cause an increase of
2.0 mg/L orthophosphate (PO
4
3-
).
d) If these increases do not occur, see Standard Additions
(Section 1) for more information.
Standard Solution Method
Prepare a 10.0-mg/L phosphate standard by pipetting 10.0 mL of
a Phosphate Standard Solution, 50 mg/L as PO
4
3-
into a 50-mL
volumetric flask. Dilute to volume with deionized water.
Or, prepare a 10.0-mg/L PO
4
3-
standard solution by using the
TenSette Pipet to add 1.00 mL of Phosphate PourRite Ampule
Standard,
500 mg/L as PO
4
3-
, into a 50-mL volumetric flask. Dilute to
volume
with deionized water.
Substitute this standard for the sample and perform the test as
described. The mg/L PO
4
3-
reading should be 10 mg/L.
Method Performance
Precision
In a single laboratory using a standard solution of 15.0 mg/L
PO
4
3-
and two lots of reagent with the instrument, a single
operator obtained a standard deviation of ±0.12 mg/L PO
4
3-
.
Estimated Detection Limit
The estimated detection limit for program 85 is 0.14 mg/L PO
4
3-
.
For more information on the estimated detection limit, see
Section 1.
PHOSPHORUS, REACTIVE, continued