Hach DR/850 - Page 204

204
Sampling and Storage
Collect samples in acid-cleaned plastic or glass bottles. If prompt
analysis is impossible, preserve the sample by adjusting to pH 2
or less with hydrochloric acid (about 2 mL per liter). Preserved
samples may be stored up to six months at room temperature. If
reporting only dissolved iron, filter the sample immediately after
collection and before adding the acid.
Before analysis, adjust the sample pH to between 3 and 4 with 5.0
N Sodium Hydroxide Standard Solution. Do not exceed pH 5 as
iron may precipitate. Correct the test result for volume; see
Correction for Volume Additions in Section 1.
Accuracy Check
Standard Additions Method
a) Snap the top off an Iron PourRite Ampule Standard
Solution,
25 mg/L Fe.
b) Use the TenSette Pipet to add 0.2, 0.4 and 0.6 mL of
standard to three 50-mL samples. Swirl gently to mix.
c) Analyze each sample as described above. The iron
concentration should increase by 0.1 mg/L for each 0.2
9.
Insert the blank in the
cell holder. Tightly
cover the sample cell
with the instrument cap.
10. Press: ZERO
The cursor will move to
the right, then the
display will show:
0.00 mg/L Fe
Note: If Reagent Blank
Correction is on, the
display may flash “limit”.
See Section 1.
11. After the timer
beeps, place the
prepared sample in the
cell holder. Tightly
cover the sample cell
with the
instrument cap.
Note: For samples
containing high levels of
molybdate (≥100 mg/L),
read the sample
immediately after zeroing
the blank.
12. Press: READ
The cursor will move to
the right, then the result
in mg/L iron will be
displayed.
Note: Standard Adjust may
be performed using a
prepared standard (see
Section 1).
IRON, TOTAL, continued