Taylor K-8000, User Manual, Page: 21 / 100

2-3 TTi
®
Colorimeter User’s Manual
Part 2 Testing Primer
INTRODUCTION TO COLORIMETRIC ABSORPTION ANALYSIS
Colorimetric absorption analysis, as used in this manual, refers to a technique for determining the concentra-
tion of various constituents of a water sample by adding reagents that selectively react with the substance being
analyzed to produce a color then measuring the absorbance of the resulting color to determine the substance
concentration.
Visible light (as opposed to ultraviolet, infrared, etc.) is a type of electromagnetic radiation that can be seen
by the human eye. It consists of wavelengths ranging from approximately 400 to 700 nm. When visible light
passes through a colored solution, certain wavelengths are selectively and strongly absorbed while other
wavelengths pass through without being absorbed. This principle of absorption provides a means for quanti-
fication based on the Beer-Lambert Law, which states the concentration of a substance in solution is directly
proportional to both the absorbance and viewdepth of the solution. It is interesting to note the wavelengths
strongly absorbed by a colored solution correspond to colors which are complementary to the color of the
solution. For example, a yellow solution strongly absorbs violet wavelengths, a blue solution strongly absorbs
orange wavelengths, and a red solution strongly absorbs green wavelengths. Many substances in water samples
are colorless, so reagents must be added that selectively react with the analyte to produce a color that will
absorb specific wavelengths of visible light.
Illustration of complementary colors on a color wheel
YELLOW
RED
ORANGE
VIOLET
BLUE
GREEN
RED
YELLOW
GREEN
GREEN
RED
VIOLET
YELLOW
ORANGE
ORANGE
BLUE
VIOLET
BLUE
Taylor’s TTi
®
Colorimeter is an optical instrument for colorimetric absorption analysis which incorporates
light-emitting diodes (LEDs) to produce visible light, wavelength filters to isolate narrow bands of light that
pass through the sample, photoelectric detectors to convert light that passes through the sample into a useable
signal, a signal processor, and software to determine the concentration of a sample. In general, to perform an
instrumental absorption analysis, the instrument is first ZEROED with a blank (usually a sample containing
no reagents) to compensate for inherent color in the sample. Next, a sample containing all necessary reagents
is READ and the concentration is computed and displayed.
BEST PRACTICES
Proper technique is essential for obtaining accurate results when performing a water test. False test results can
lead the analyst into making an incorrect evaluation of the condition of the water, thereby applying the wrong
corrective actions to a system. The following practices will help you obtain reliable test results.