45-21
COLOR, TRUE AND APPARENT, continued
13. Press: READ
The display will
count down to 0.
Then the display will
show the results in
PtCo color units.
SAMPLING AND STORAGE
Collect samples in clean plastic or glass bottles. Most reliable results
are obtained when samples are analyzed as soon as possible after the
collection. If prompt analysis is impossible, full bottles completely and
cap tightly. Avoid excessive agitation or prolonged contact with air.
Sample can be stored for 24 hours by cooling to 4 °C (39 °F). Warm to
room temperature before testing.
ACCURACY CHECK
Standard Solution Method
A 500 platinum-cobalt units color standard solution is available under
Optional Reagents for checking test accuracy. A 250 platinum-cobalt
units standard can be made by pipetting 50.0 mL of the 500 platinum-
cobalt units standard into a 100-mL volumetric flask and diluting to
volume with demineralized water.
STATISTICAL EVALUATION
A single operator repetitively tested samples of two laboratory prepared
solutions, using one DR/700, matched sample cells and two
representative lots of reagent. Testing 500 color units concentration
solutions, the standard deviation was ±7.0 color units.
Testing zero concentration samples, the limit of detection was 4.2 mg/L
color units. The limit of detection was calculated as three times the
standard deviation when testing zero concentration samples (adapted
from Analytical Chemistry, 1980, 52, 2242-2249).
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