Hach DR/700 Procedures Manual page 112

NICKEL,
continued
SAMPLING AND STORAGE
Collect samples in acid-washed plastic bottles. Adjust the sample pH to
2 or less with nitric acid (about 5 mL per liter). Preserved samples can
be stored up to six months at room temperature. Before analysis, adjust
the sample pH to between 3 and 8 with 5.0 N Sodium Hydroxide
Standard Solution. Do not exceed pH 8 as this may cause some loss of
nickel as a precipitate. Correct the test results for volume additions; see
Sampling and Storage, Volume Additions, (Section I) for more
information.
ACCURACY CHECK
Standard Additions Method
a) Snap the neck off a Nickel Voluette Ampule Standard Solution,
300 mg/L Ni.
b) Use the TenSette Pipet to add 0.1, 0.2 and 0.3 mL of standard to three
300-mL samples.
c) Analyze each sample as described above. The nickel concentration
should increase 0.10 mg/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
Prepare a 1.0 mg/L nickel standard solution by diluting 50.0 mL of a
10-mg/L working standard solution to 500 mL in a volumetric flask.
The working stock solution should be prepared daily by diluting
10.00 mL of Nickel Standard Solution, 1000 mg/L as Ni, to 1000 mL
with demineralized water.
Or, use the TenSette Pipet to add 1.0 mL of a Nickel Voluette Ampule
Standard Solution, 300 mg/L Ni, into a 500-mL volumetric flask and
dilute to volume with demineralized water. This solution is 0.6 mg/L
nickel.
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 testing reagents. Testing 1.00 mg/L Ni
concentration samples, the standard deviation was ±0.026 mg/L Ni.
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