Hach DR/850, Procedures Manual, Page: 330 / 460

330
Sampling and Storage
The main consideration in this procedure is to prevent
contaminating the sample with atmospheric oxygen. Sampling
from a stream of water that is hard plumbed to the sample source
is ideal. Use a funnel to maintain a continual flow of sample and
yet collect enough sample to immerse the ampul. It is important
not to introduce air in place of the sample. Rubber tubing, if used,
will introduce unacceptable amounts of oxygen into the sample
unless the length of tubing is minimized and the flow rate is
maximized. Flush the sampling system with sample for at least
5 minutes.
Accuracy Check
The reagent blank for this test can be checked by following these
steps:
a) Fill a 50-mL beaker with sample and add approximately
50 mg sodium hydrosulfite.
b) Immerse the tip of a Low Range Dissolved Oxygen
AccuVac Ampul in the sample and break the tip. Keep the
tip immersed while the ampul fills completely.
c) Determine the dissolved oxygen concentration according
to the preceding procedure. The result should be
0 ±1 µg/L.
Method Performance
Precision
In a single laboratory, using a standard solution of 500 µg/L O
2
and two representative lots of reagent with the instrument, a
single operator obtained a standard deviation of
±
2 µg/L O
2
. For
more information on Hach’s precision statement, see Section 1 .
Estimated Detection Limit
The estimated detection limit for program #71 is 10 µg/L O
2
. For
more information on the estimated detection limit, see Section 1 .
OXYGEN, DISSOLVED, Low Range,
continued