LaMotte COD Plus Colorimeter 1922-EX2 - Manual (Page 13)

Below is a list of suggested wavelengths for the color of the reacted samples.
Use these as a starting point.
Sample
Color
Wavelength
Range
Yellow 430
Pink 520
Red 570
Green and Blue 620
NOTE: Available wavelengths in the COD PLUS are 430 nm and 620 nm
only.
n
CALIBRATION CURVES
The COD PLUS Colorimeter contains precalibrated tests for the LaMotte
reagent systems (p. 49). The first step in using a non-LaMotte reagent system
with your COD PLUS Colorimeter is to create a calibration curve for the
reagent system. To create a calibration curve, prepare standard solutions of the
test factor and use the reagent system to test the standard solutions with the
COD PLUS Colorimeter. Select a wavelength for the test as described above.
Plot the results (in ABS or %Transmittance) versus concentration to create a
calibration curve. The calibration curve may then be used to identify the
concentration of an unknown sample by testing the unknown, reading
Absorbance or %T, and finding the corresponding concentration from the
curve. The linear range of the reagent system can be determined and this
information can be used to input a User Test into the COD PLUS Colorimeter
(see EDIT USER TESTS, p. 36).
n PROCEDURE
1. Prepare 5 or 6 standard solutions of the factor being tested. The
concentration of these standards should be evenly distributed throughout
the range of the reagent system, and should include a 0 ppm standard
(distilled water). For instance, the solutions could measure 0, 10%, 30%,
50%, 70%, and 90% of the system’s maximum range.
2. Turn on the COD PLUS Colorimeter. Select the appropriate wavelength
from the absorbance mode. Be sure to select the appropriate wavelength for
the color produced by the reagent system.
3. Use the unreacted 0 ppm standard to standardize the colorimeter by using it
to scan blank.
4. Following the individual reagent system instructions, react each standard
solution beginning with 0 ppm. Continue with standards in increasing
concentration. Record the reading and the standard solution concentration
on a chart. Readings can be recorded as percent transmittance (%T) or
absorbance (A).
COD PLUS COLORIMETER 6/02 13