Hach DR/850, Procedures Manual, Page: 401 / 460

401
Sampling and Storage
Collect samples in clean plastic or glass bottles. Analyze samples
as soon as possible after collection. Store samples up to 28 days at
4
° C (39 ° F) or below. Warm samples to room temperature before
analyzing.
Accuracy Check
Standard Additions Method
a) Open a High Range Silica Standard Solution, 1000 mg/L
SiO
2
.
b) Use the TenSette Pipet to add 0.1 mL, 0.3 mL, and 0.5 mL
of the standard to three 10-mL samples. Mix each
thoroughly.
c) Analyze each sample as described above. The silica
concentration should increase 4 mg/L for each 0.1 mL of
standard added.
d) If these increases do not occur, see Standard Additions in
Section 1 for more information.
Standard Solution Method
To prepare a 160-mg/L silica standard, pipet 40.0 mL of a 1000-
mg/L Silica Standard Solution into a 250-mL volumetric flask.
Dilute to the line with deionized water. Analyze according to the
above procedure using deionized water as the blank.
Standard Adjust
To adjust the calibration curve using the reading obtained with
the
160-mg/L standard solution, press the
SETUP
key and scroll
(using the arrow keys) to the STD setup option. Press
ENTER
to
activate the standard adjust option. Then enter
160.
to edit the
standard concentration to match that of the standard used. Press
ENTER
to complete the adjustment. See Section 1 , Standard
Curve Adjustmen t for more information.
Method Performance
Precision
In a single laboratory, using a standard solution of 100.0 mg/L
SiO
2
and two representative lots of reagent with the instrument, a
single operator obtained a standard deviation of
±
2.0 mg/L silica.
SILICA, Ultra High Range,
continued