12
SMART Spectro 2 Operator’s Manual 04.16
produces a pink color proportional to the nitrate concentration in the sample (the greater
the nitrate concentration, the darker the pink color). A wavelength in the green region
should be selected to analyze this sample since a pinkish-red solution absorbs mostly
green light.
REAGENT BLANK
Some tests will provide greater accuracy if a reagent blank is determined to compensate
for any color or turbidity resulting from the reagents themselves. A reagent blank is
performed by running the test procedure on 10 mL of demineralized or deionized water.
Use sample water to SCAN BLANK. Insert the reacted reagent blank in the colorimeter
chamber and select SCAN SAMPLE. Note result of reagent blank. Perform the tests on the
sample water as described. Subtract results of reagent blank from all subsequent test
results.
NOTE: Some tests require a reagent blank to be used to SCAN BLANK.
SPECTROPHOTOMETER TUBES
Spectrophotometer tubes which have been scratched through excessive use should be
discarded and replaced with new ones. Dirty tubes should be cleaned on both the inside
and outside. Fingerprints on the exterior of the tubes can cause excessive light scattering
and result in errors. Handle the tubes carefully, making sure the bottom half of the tube is
not handled.
LaMotte Company makes every eff ort to provide high quality spectrophotometer tubes.
However, wall thicknesses and diameter of tubes may still vary slightly. This may lead to
slight variations in results (e.g. if a tube is turned while in the sample chamber, the reading
will likely change slightly). To eliminate this error put the tubes into the sample chamber
with the same orientation every time.
The tubes that are included with the spectrophotometer have an index mark to facilitate
this. If possible, use the same tube to SCAN BLANK and SCAN SAMPLE.
SELECTING AN APPROPRIATE WAVELENGTH
The most appropriate wavelength to use when creating a calibration curve is usually the
one which gives the greatest change from the lowest reacted standard concentration
to the highest reacted standard concentration. However, the absorbance of the highest
reacted standard concentration should never be greater than 2.0 absorbance units.
Scan the lowest and highest reacted standards at diff erent wavelengths using the %T/
ABS mode to fi nd the wavelength which gives the greatest change in absorbance without
exceeding 2.0 absorbance units. Use this wavelength to create a calibration curve.
A list of suggested wavelength ranges for the color of the reacted samples follows. Use
these as a starting point.
www.
GlobalScientificSupply
.com
GLOBAL SCIENTIFIC SUPPLY
The Laboratory Supply Company!
