61-16
CYANIDE, continued
16. Place the
prepared sample in
the cell holder.
Note: In bright light it
may be necessary to
close the cell
compartment cover.
17. Press: READ
The display will
count down to 0.
Then the display will
show the results in
mg/L cyanide (CN
-
).
SAMPLING AND STORAGE
Samples collected in glass or plastic bottles should by analyzed as
quickly as possible. The presence of oxidizing agents, sulfides and fatty
acids can cause the loss of cyanide during sample storage. Samples
containing these substances must be pretreated as described in the
following procedures before preservation with sodium hydroxide. If the
sample contains sulfide and is not pretreated, it must be analyzed within
24 hours.
To preserve the sample, adjust the pH above 12 by adding 4.0 mL of
5.0 N Sodium Hydroxide Standard Solution to each liter (or quart) of
sample, using a glass serological pipet and pipet filler. Check the
sample pH to be sure it is above 12. Four mL of sodium hydroxide is
usually enough to raise the pH of most water and wastewater samples to
12. Add more 5.0 N sodium hydroxide if necessary. Store the samples
at 4 °C (39 °F) or less. Samples preserved in this manner can be stored
for 14 days.
Before testing, samples preserved with 5.0 N sodium hydroxide or
samples that are highly alkaline due to chlorination treatment processes
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