Hach DR/700 Procedures Manual page 487

IRON,
continued
ACCURACY CHECK
Standard Additions Method
a) Snap the neck off an Iron Volute Ampule Standard, 25 mg/L Fe.
b) Use the TenSette Pipet to add 0.1 mL of standard to the prepared
sample measured in Step 11.
c) Swirl to mix and allow another five-minute reaction period, then
measure the iron concentration as in Step 11.
d) Add two additional 0.1 mL standard increments, taking a
concentration reading after allowing the five-minute reaction period for
each.
e) Each additional 0.1 mL increment of standard added should cause a
0.1 mg/L increase in the concentration reading.
f) If these increases do not occur, see Standard Additions (Section I) for
more information.
Standard Solution Method
Prepare a 0.4 mg/L iron working solution as follows:
a) Pipet 1.00 mL of iron standard solution, 100 mg/L Fe, into a 250-mL
volumetric flask.
b) Dilute to volume with demineralized water. This solution should be
prepared daily. Analyze the working solution according to the above
procedure.
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 0.500 mg/L Fe
concentration samples, the standard deviation was ±0.0024 mg/L Fe.
Testing zero concentration samples, the limit of detection was
0.0044 mg/L Fe. 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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