Hach DR/850 Procedures Manual page 211

IRON, TOTAL,
Method Performance
continued
d) Add two additional 0.1-mL aliquots of standard,
measuring the concentration after each addition. The iron
concentration should increase by 0.25 mg/L for each 0.1-
mL addition of standard.
e) If these increases do not occur, see Standard Additions in
Section 1 for more information.
Standard Additions Method (AccuVac Ampuls)
a) Use a graduated cylinder to measure 25.0 mL of sample
into each of three 50-mL beakers.
b) Snap the neck off an Iron Ampule Standard, 25 mg/L Fe.
c) Using a TenSette Pipet, add 0.1, 0.2 and 0.3 mL of
standard, respectively, to the 50-mL beakers. Swirl to mix.
d) Fill a TPTZ AccuVac Ampul from each beaker.
e) Measure the concentration of each ampul according to the
procedure. The iron concentration should increase by 0.1
mg/L for each 0.1 mL addition of standard.
f) If these increases do not occur, see Standard Additions in
Section 1 for more information.
Standard Solution Method
Prepare a 0.4 mg/L iron working solution as follows:
a) Using Class A glassware, pipet 1.00 mL of Iron Standard
Solution, 100 mg/L Fe, into a 250-mL volumetric flask.
b) Dilute to volume with deionized water. Stopper and invert
repeatedly to mix. Prepare this solution daily.
Precision
In a single laboratory using a standard solution of 1.00 mg/L Fe
and two representative lots of reagent with the instrument, a
single operator obtained a standard deviation of ±0.017 mg/L Fe.
In a single laboratory using a standard solution of 1.00 mg/L Fe
and one representative lot of AccuVac Ampuls with the
instrument, a single operator obtained a standard deviation of
±0.022 mg/L Fe.
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