Hach DR/850, Procedures Manual, Page: 31 / 460

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CHEMICAL ANALYSIS INFORMATION
, continued
Using Sample Cells
Orientation of Sample Cells
Two round sample cells are shipped with the DR/820, DR/850 and
DR/890. They are marked with 10-, 20- and 25-mL fill lines which may
be used to measure the sample volume unless the procedure instructs you
to use other glassware to measure the sample volume.
To minimize variability of measurements using a particular cell, always
place the cell into the cell holder with the same orientation. The cells are
placed in the instrument with the fill marks facing the user.
In addition to proper orientation, the sides of the cells should be free of
smudges, fingerprints, etc. to ensure accurate readings. Wipe the sides of
the cells with a moist cloth followed by a dry soft cloth to clean the surface
before taking measurements.
Care of Hach Sample Cells
Store sample cells in their boxes when not in use to protect them from
scratching and breaking. It is good laboratory practice to empty and
clean sample cells after analyses are complete--avoid leaving colored
solutions in the cells for extended periods of time. Finish the cleaning
procedure with a few rinses of deionized water and allow to dry.
Individual procedures often recommend specific cleaning methods.
Cleaning Sample Cells
Most laboratory detergents can be used at recommended concentrations.
Neutral detergents such as Neutracon are safer if regular cleaning is
required, as in the case of protein residues.
If using a detergent, you can speed cleaning by increasing the temperature
or using an ultrasonic bath.
Rinsing is more efficient when using deionized water.
Using the COD/TNT Adapter
Use care when seating a vial into the COD/ TNT adapter (for COD vials
and Test ‘N Tubes). Place the vial into the adapter and press straight down
on the top of the vial until it seats solidly. Do not move the vial from side
to side; this can cause errors.
Volume Measurement Accuracy
The sample cells supplied with the instrument have fill marks to indicate
10, 20 or 25 mL. The fill marks are intended to measure the volume to be
analyzed. Do not use these fill marks to perform sample dilutions.
If a sample must be diluted, use a pipet, graduated mixing cylinder and/or
a volumetric flask for accurate measurement. When diluting, accuracy is
important because a slight mistake in measuring a small sample will cause