Hach DR/850 Procedures Manual page 157

CYANIDE,
continued
13.
Place the blank into
the cell holder. Tightly
cover the sample cell
with the instrument cap.
Sampling and Storage
14.
Press:
ZERO
The cursor will move to
the right, then the
display will show:
0.000 mg/L CN
Note: If Reagent Blank
Correction is on, the
display may flash "limit".
See Section 1.
Collect samples in glass or plastic bottles and analyze as soon as
possible.
The presence of oxidizing agents, sulfides and fatty acids can
cause cyanide loss 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.
Preserve the sample 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. Four mL of sodium hydroxide are 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 or distillation procedures should be adjusted to
approximately pH 7 with 2.5 N Hydrochloric Acid Standard
15.
Place the prepared
sample into the cell
holder. Tightly cover the
sample cell with the
instrument cap.
157
16.
Press:
READ
The cursor will move to
the right, then the result
in mg/L cyanide (CN)
will be displayed.
Note: Standard Adjust may
be performed using a
prepared standard
(see Section 1).