Hach DR/700 Procedures Manual page 97

COPPER,
continued
SAMPLING AND STORAGE
Collect samples in acid-washed plastic bottles. To preserve, adjust the
pH to 2 or less with nitric acid (about 5 mL per liter). Store preserved
samples up to six months at room temperature.
Before testing, adjust the pH of the sample to between 2 and 6. If the
sample is too acidic, adjust the pH with 5.0 N Sodium Hydroxide
Standard Solution. Correct test results for volume additions; see
Sampling and Storage, Volume Additions, (Section I) for more
information.
ACCURACY CHECK
Standard Additions Method
a) Using a TenSette Pipet, add 0.1 mL of Copper Standard Solution,
10.0 mg/L Cu, to two sample cells containing 25 mL of sample.
b) Repeat, using 0.2 mL and 0.3 mL additions of standard.
c) Analyze the samples as described above. The copper concentration
reading should increase by 40 µg/L for each 0.1 mL of standard added.
d) If these increases do not occur, see Standard Additions (Section I) for
more information.
Standard Solution Method
To assure the accuracy of the test, prepare a 100-µg/L copper standard:
a) Pipet 1.00 mL of copper standard solution, 10.0 mg/L Cu, into a
100-mL volumetric flask.
b) Dilute to volume with copper-free, reagent-grade water.
c) Use this standard in place of the sample in the procedure.
d) Prepare this solution daily.
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 150 µg/L Cu concentration
solutions, the standard deviation was ±1.2 µg/L Cu.
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