Hach DR/700 Procedures Manual page 654

ZINC,
continued
13.
Within 10
minutes of the three-
minute period, place
the prepared sample
in the cell holder.
Note: In bright light it
may be necessary to
close the cell
compartment cover.
SAMPLING AND STORAGE
Collect samples in acid-washed plastic bottles. For storage, adjust the
pH to 2 or less with nitric acid (about 2 mL per liter). The preserved
samples can be stored for up to six months at room temperature. Adjust
the pH to 4 to 5 with 5.0 N Sodium Hydroxide before analysis. Do not
exceed pH 5, as zinc may be lost as a precipitate. Correct the test result
for volume additions; see Sampling and Storage, Volume Additions,
(Section I) for more information. If only dissolved zinc is to be
determined, filter the sample before acid addition.
ACCURACY CHECK
Standard Additions Method
a) Snap the neck off a Zinc Voluette Ampule Standard Solution, 25 mg/L.
b) Use the TenSette pipet to add 0.2, 0.4, and 0.6 mL of standard to three
50-mL samples. Mix each thoroughly.
14.
Press:
READ
The display will
count down to 0.
Then the display will
show the results in
mg/L zinc (Zn).
Note: Determine a
reagent blank for each
lot of reagent by
running the procedure
on demineralized water.
Subtract this value from
all following results
obtained in Step 14.
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