Hach DR/700 Procedures Manual page 472

COPPER,
continued
SAMPLING AND STORAGE
Collect samples in acid-cleaned glass or plastic containers. Adjust the pH
to 2 or less with nitric acid (about 2 mL per liter). Store preserved samples
up to six months at room temperature. Before analysis, adjust the pH to 4
to 6 with 8 N potassium hydroxide. Do not exceed pH 6, as copper may
precipitate. Correct the test result for volume additions; see Sampling and
Storage, Volume Additions, (Section I) for more information. If only
dissolved copper is to be determined, filter the sample before acid addition
using the labware listed under Optional Apparatus.
ACCURACY CHECK
Standard Additions Method
a) Snap the neck off the Copper Voluette Ampule Standard Solution,
75 mg/L.
b) Use the TenSette Pipet to add 0.1, 0.2, and 0.3 mL of standard to three
25-mL samples. Mix each thoroughly. (For AccuVac Ampuls, use 50-mL
beakers.)
c) Analyze each sample as described above. The copper concentration
should increase 0.3 mg/L for each 0.1 mL of standard added.
d) If these increases do not occur, see Standard Addition (Section I) for
more information.
Standard Solution Method
Prepare a 1.00-mg/L copper standard by diluting 1.00 mL of Copper
Standard Solution, 100 mg/L as Cu, to 100 mL with demineralized
water. 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 2.50 mg/L Cu concentration
solutions, the standard deviation was ±0.012 mg/L Cu.
Testing zero concentration samples, the limit of detection was 0.014 mg/L
Cu. 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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