Hach DR/850, Procedures Manual, Page: 399 / 460

399
Method 10098
SILICA, Ultra High Range
(0 to 200 mg/L) For water and seawater
Silicomolybdate Method
1.
Enter the stored
program number for
ultra high range silica
(SiO
2
).
Press:
PRGM
The display will show:
PRGM ?
Note: For most accurate
results, perform a Reagent
Blank Correction using
deionized water (see
Section 1).
2.
Press:
88 ENTER
The display will show
mg/L, SiO2 and the
ZERO icon .
Note: For alternate form
(Si), press the CONC key.
3.
Fill 2 sample cells
with 10 mL of sample.
Note: Sample temperature
should be 15 to 25 °C
(59 to 77 °F).
4.
Fill both sample cells
to the 25-mL line with
deionized water. Set one
sample cell aside as
the blank.
5.
To the other cell, add
the contents of one
Molybdate Reagent
Powder Pillow for High
Range Silica (the
prepared sample). Cap
and invert to mix.
6.
Add the contents of
one Acid Reagent
Powder Pillow for
High Range Silica to the
prepared sample. Cap
and invert to mix.
Note: Silica or phosphate
will cause a yellow color to
develop.
7.
Press:
TIMER ENTER
A 10-minute reaction
period will begin.
8.
When the timer
beeps, add the contents
of one Citric Acid
Powder Pillow to the
prepared sample. Cap
and invert to mix.
Note: The yellow color due
to phosphate will
disappear.