Environmental Engineering Reference
In-Depth Information
Note: Some of the methods used by volunteer monitors are based directly
on procedures outlined in the APHA Standard Methods . Although many
methods used by volunteer monitors are not described in Standard
Methods , they can be standardized to provide repeatable and comparable
data. Instructions, training, and audit procedures all play a role in stan-
dardizing the methods used by volunteer monitors.
Test Methods*
Descriptions of general methods to help you understand how each works
in specific test kits follow. Always follow the specific instructions included
with the equipment and individual test kits. Most water analyses are con-
ducted either by titrimetric analyses or colorimetric analyses. Both methods
are easy to use and provide accurate results.
Titrimetric
Titrimetric analyses are based on adding a solution of known strength (the
titrant ) to a specific volume of a treated sample in the presence of an indica-
tor. The indicator produces a color change indicating that the reaction is com-
plete. Titrants are generally added by a titrator (microburette) or a precise
glass pipette.
Colorimetric
Two basic types of colorimetric tests are commonly used:
1. The pH is a measure of the concentration of hydrogen ions (the acid-
ity of a solution) determined by the reaction of an indicator that var-
ies in color, depending on the hydrogen ion levels in the water.
2. Tests that determine a concentration of an element or compound
are based on Beer's law. Simply, this law states that the higher the
concentration of a substance, the darker the color produced in the
test reaction and therefore the more light absorbed. Assuming a
constant viewpath, the absorption increases exponentially with
concentration.
* Much of the information presented in the following sections is adapted from Standard
Methods (APHA, 1998), Federal Register , and The Monitor's Handbook (LaMotte, 1992).
 
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