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BROMINE,
d
continue
ACCURACY CHECK
Standard Additions Method
a) Snap the top off a Chlorine Voluette Ampule Standard Solution.
b) Use the TenSette Pipet to add 0.1, 0.2, and 0.3 ml of standard to three
25-mL samples. Swirl gently to mix. (For AccuVac Ampuls, use
50-mL beakers.)
c) Analyze each sample as described above. Each 0.1 mL of standard
will cause an incremental increase in bromine, the exact value of which
depends on the chlorine concentration in the Voluette. Check the
certificate enclosed with the Voluettes for the incremental chlorine
value; then multiply by 2.25 to obtain the value for bromine.
d) If these increases do not occur, see Standard Additions (Section I) for
more information.
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 1.00 mg/L Cl
(equivalent to
2
2.25 mg/L Br
) concentration solutions, the standard deviation was
2
±0.005 mg/L CL
(equivalent to 0.01 mg/L Br
).
2
2
Testing zero concentration samples, the limit of detection was 0.010 mg/L
Cl
(equivalent to 0.02 mg/L Br
). The limit of detection was calculated
2
2
as three times the standard deviation when testing zero concentration
samples (adapted from Analytical Chemistry, 1980, 52, 2242-2249).
Using two representative lots of AccuVacs, the standard deviation was
±0.005 mg/L Cl
(equivalent to 0.01 mg/L Br
) and the limit of detection
2
2
was 0.015 mg/L Cl
(equivalent to 0.03 mg/L Br
).
2
2
INTERFERENCES
Samples containing more than 300 mg/L alkalinity or 150 mg/L acidity
as CaCO
may not develop the full amount of color, or it may instantly
3
fade. Neutralize these samples to a pH of 6 to 7 with 1 N sulfuric acid or
1 N sodium hydroxide. Determine the amount required on a separate
25 mL sample. Add the same amount to the sample to be tested. Correct
the test result for volume additions; see Sampling and Storage, Volume
Additions, (Section I) for more information.
52-34
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