Hach DR/700 Procedures Manual page 524

IRON, TOTAL,
continued
ACCURACY CHECK
Standard Additions Method
Using AccuVac Ampuls
a) Measure 25.0 mL of sample using a graduated cylinder into each of
three 50-mL beakers.
b) Snap the neck off a Volute Ampule Standard for Iron, 25 mg/L Fe.
c) Add 0.1, 0.2 and 0.3 mL of standard, respectively, to the three 50-mL
beakers using the TenSette Pipet. Swirl to mix.
d) Fill a TPTZ Iron AccuVac Ampul completely from each beaker.
e) Measure the concentration of each ampul according to the above
procedure. The iron concentration reading should increase by 0.1 mg/L
for each 0.1 mL addition of standard.
f) If these increases does not occur, see Standard Additions, (Section I)
for more information.
Standard Solutions 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. Prepare this solution
fresh 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 0.75 mg/L Fe
concentration samples, the standard deviation was ±0.035 mg/L Fe.
Testing zero concentration samples, the limit of detection was 0.080 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).
Using two representative lots of AccuVac Ampuls, the standard deviation
was ±0.019 mg/L Fe and the limit of detection was ±0.035 mg/L Fe.
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