Hach DR/850, Procedures Manual, Page: 393 / 460

393
Method 8186
SILICA, Low Range
(0 to 1.60 mg/L)
For water and seawater
Heteropoly Blue Method
*
1.
Enter the stored
program number for low
range silica (SiO
2
).
Press:
PRGM
The display will show:
PRGM ?
2.
Press:
90 ENTER
The display will show
mg/L, SiO2 and the
ZERO icon .
3.
Fill two sample
cells to the 10-mL line
with sample.
4.
Add 15 drops of
Molybdate 3 Reagent to
each sample cell. Swirl
to mix.
Note: For greatest
accuracy, hold dropping
bottle vertical.
5.
Press:
TIMER ENTER
A 4-minute reaction
period will begin.
Note: Reaction time given
is for samples at 20 °C
(68 °F). If the sample
temperature is 10 °C
(50 °F), wait 8 minutes. If
the sample temperature is
30 °C (86 °F), wait
2 minutes.
6.
After the timer
beeps, add the contents
of one Citric Acid
Reagent Powder Pillow
to each sample cell.
Swirl to mix.
7.
The display will
show:
1:00 TIMER 2
Press:
ENTER
A 1-minute reaction
period will begin.
Phosphate interference
is eliminated during
this period.
Note: The time given is for
samples at 20 °C (68 °F). If
the sample temperature is
10 °C (50 °F), wait two
minutes. If the sample is
30 °C (86 °F), wait
30 seconds.
8.
After the timer
beeps, add the contents
of one Amino Acid F
Reagent Powder Pillow
to one of the sample
cells (the prepared
sample). Invert to mix.
Note: The sample cell
without the Amino Acid F
Reagent is the blank.
* Adapted from Standard Methods for the Examination of Water and Wastewater.