Hach DR/850, Procedures Manual, Page: 47 / 460

47
CHEMICAL ANALYSIS INFORMATION
, continued
Reagent Blank Correction
The Reagent Blank Correction subtracts the color absorbed when running
the test with deionized water instead of sample. The blank value is
subtracted from every result to correct for any background color due to
reagents.
When using the Reagent Blank Correction feature, the blank correction
should be entered before the Standard Adjust feature is used.
To enter a programmed correction for the reagent blank:
1. Run the test using deionized water with each new lot of reagents.
2. Press
READ
to obtain the blank value.
3. Press
SETUP
, scroll to
BLANK
and press
ENTER
. The display will
show
BLANK?
.
4. Enter the blank value just read from the instrument.
5. Press
ENTER
to accept the value as the blank to be subtracted from
each reading.
6. The display will show 0.00 mg/L (resolution and units vary) and the
sample cell icon will be displayed, indicating that the reagent blank
feature is enabled and the blank value will be subtracted from each
reading. Repeat the reagent blank adjust for each new lot of reagents.
Note: After entering a reagent blank adjust, the display may flash “limit” when zeroing if
the sample used for zeroing has a lower absorbance value than the reagent blank.
To disable the Reagent Blank adjust feature, press
SETUP
, scroll to
BLANK
and press
ENTER
twice. The concentration readings will be
displayed without subtracting the blank. The sample cell icon will no
longer appear in the display.
Do not use the Reagent Blank Adjust feature if the procedure uses a
reagent blank for zeroing.
Standard Adjust (Adjusting the Standard Curve)
The colorimeter has Hach Programs permanently installed in memory. A
program usually includes a pre-programmed calibration curve. Each curve
is the result of an extensive calibration performed under ideal conditions
and is normally adequate for most testing. Deviations from the curve can
occur from using compromised testing reagents, defective sample cells,
incorrect test procedure, incorrect technique, or other correctable causes.
Interfering substances or other causes may be beyond the analyst’s control.