Hach DR/700 Procedures Manual page 321

VOLATILE ACIDS,
continued
SAMPLING AND STORAGE
Collect samples in plastic or glass bottles. Analyze sample as soon as
possible after collection. Samples can be stored up to 24 hours by
cooling to 4 °C (39 °F) or below. Warm to room temperature before
running the test.
ACCURACY CHECK
Standard Additions Method
a) Snap the neck off a Volatile Acids Voluette Ampule Standard
Solution, 62,500 mg/L as acetic acid.
b) Use the TenSette Pipet to add 0.1, 0.2, and 0.3 mL of standard to three
25-mL graduated mixing cylinders containing 25 mL of filtered sample.
Stopper. Shake well to mix.
c) Remove a 0.5 mL aliquot of sample from each cylinder; add to a
sample cell. All three samples can be analyzed along with the original
test sample beginning with Step 7 of the procedure. The volatile acid
concentration should increase 250 mg/L volatile acids as acetic acid for
each 0.1 mL of standard added.
d) If these increases do not occur, see Standard Additions (Section I) for
more information.
Standard Solution Method
Prepare a 500 mg/L volatile acid standard by using the TenSette Pipet to
add 0.8 mL of a Volatile Acids Voluette Ampule Standard Solution to a
100-mL volumetric flask. Dilute to volume with demineralized water.
STATISTICAL EVALUATION
A single operator repetitively tested samples of two prepared solutions,
using one DR/700, matched sample cells and two representative lots of
testing reagents. Testing 1250 mg/L as HOAc concentration samples,
the standard deviation was ±4.5 mg/L HOAc.
Testing zero concentration samples, the limit of detection was 23.5 mg/L
HOAc. 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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