Hach DR/700 Procedures Manual page 331

ALUMINUM,
continued
SAMPLING AND SRORAGE
Collect samples in a cleaned glass or plastic container. To preserve the
sample adjust the pH to 2 or less with nitric acid (about 1.5 mL per liter).
Preserved samples can be stored up to six months at room temperature.
Before analysis, adjust the pH to 3.5 to 4.5 with 5.0 N Sodium
Hydroxide. Correct the test result for volume additions; see Sampling
and Storage, Volume Additions, (Section I) for more information.
ACCURACY CHECK
Standard Additions Method
a) Snap the neck off an Aluminum Voluette Ampule Standard Solution,
50 mg/L Al.
b) Use the TenSette Pipet to add 0.1 mL, 0.2 mL and 0.3 mL of standard,
respectively, to three 50-mL samples. Mix each thoroughly.
c) Analyze each sample as described above. The aluminum
concentration should increase 0.1 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 0.4-mg/L aluminum standard solution by pipetting 1.00 mL of
3+
Aluminum Standard Solution, 100 mg/L as Al , into a 250-mL
volumetric flask. Dilute to the mark with demineralized water. Prepare
this solution daily. Perform the aluminum procedure as described above.
The mg/L Al reading in Step 14 should be 0.4 mg/L Al.
Or, using the TenSette pipet, add 0.8 mL of solution from a Aluminum
Voluette Ampule Standard Solution (50 mg/L as Al) into a 100-mL
volumetric flask. Dilute 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 0.50 mg/L Al concentration
solutions, the standard deviation was ±0.009 mg/L Al.
Testing zero concentration samples, the limit of detection was
52-5