Hach DR/850, Procedures Manual, Page: 326 / 460

326
Sampling and Storage
The main consideration in sampling with the High Range
Dissolved Oxygen AccuVac Ampul is to prevent the sample from
becoming contaminated with atmospheric oxygen. This is
accomplished by capping the ampul with an ampul cap in the
interval between breaking open the ampul and reading the
absorbance. If the ampul is securely capped, it should be safe
from contamination for several hours. The absorbance will
decrease by approximately 3% during the first hour and will not
change significantly afterwards.
Sampling and sample handling are important considerations in
obtaining meaningful results. The dissolved oxygen content of
the water being tested can be expected to change with depth,
turbulence, temperature, sludge deposits, light, microbial action,
mixing, travel time and other factors. A single dissolved oxygen
test rarely reflects the accurate over-all condition of a body of
water. Several samples taken at different times, locations and
depths are recommended for most reliable results. Samples must
be tested immediately upon collection although only a small error
results if the absorbance reading is taken several hours later.
9.
Press:
ZERO
The cursor will move to
the right, then the
display will show:
0.0 mg/L O2
Note: If Reagent Blank
Correction is on, the
display may flash “limit”.
See Section 1.
10.
Place the AccuVac
ampul into the cell
holder. Tightly cover the
ampul with the
instrument cap. Wait
approximately 30
seconds for the air
bubbles to disperse from
the light path.
11.
Press:
READ
The cursor will move to
the right, then the result
in mg/L O
2
will
be displayed.
Note: Standard Adjust may
be performed using a
prepared standard (see
Section 1).
OXYGEN, DISSOLVED, High Range,
continued