Hach DR/850 - Page 73

73
Sampling and Storage
Collect samples in a clean glass or plastic container. Preserve the sample
by adjusting 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 3.5–4.5 with 5.0 N Sodium Hydroxide.
Correct the test result for volume additions; see Correcting for Volume
Additions in Section 1 for more information.
Accuracy Check
Standard Additions Method
a) Snap the neck off an Aluminum Voluette Ampule Standard
Solution, 50 mg/L as 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. Swirl gently to
mix. Also prepare a sample without any standard added (the
unspiked sample).
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 1)
for more information.
Standard Solution Method
Prepare a 0.40-mg/L aluminum standard solution by pipetting 1.00 mL of
Aluminum Standard Solution, 100 mg/L as Al
3+
, into a 250-mL
volumetric flask. Dilute to the mark with deionized water. Prepare this
solution immediately before use. Perform the aluminum procedure as
described above. The mg/L Al reading should be 0.40 mg/L Al.
Or, using the TenSette Pipet, add 0.8 mL of solution from an Aluminum
Voluette Ampule Standard Solution (50 mg/L as Al) into a 100-mL
volumetric flask. Dilute to volume with deionized water. Prepare this
standard immediately before testing and use as the sample.
Method Performance
Precision
In a single laboratory, using a standard solution of 0.40 mg/L Al and two
representative lots of reagent with the instrument, a single operator
obtained a standard deviation of ±0.013 mg/L Al.
ALUMINUM, continued