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Cyanide
Interfering
Substance
1. Adjust a 25-mL portion of the alkaline sample to pH 7–9 with 2.5 N Hydrochloric Acid Standard Solution.
(Cat. No. 1418-32) Count the number of drops added.
2. Add four drops of Potassium Iodide Solution (Cat. No. 343-32) and four drops of Starch Indicator Solution to
the sample. Swirl to mix. The sample should be colorless.
3. Add Bromine Water (Cat. No. 2211-20) drop-wise until a blue color appears. Swirl the sample thoroughly after
Reducing
each addition. Count the number of drops.
Agents
4. Take another 25-mL sample and add the total number of drops of Hydrochloric Acid Standard Solution counted
in step a.
5. Add the total number of drops of Bromine Water counted in step c to the sample and mix thoroughly.
Continue with step 3 of the cyanide procedure.
Large amounts of turbidity will cause high readings. Use filter paper (Cat. No. 1894-57) and a funnel
Turbidity
(Cat. No. 1083-67) to filter highly turbid water samples before use in steps 2 and 11. The test results should then
be recorded as soluble cyanide.
Sample Collection, Storage and Preservation
Cyanide
Page 4 of 8
(continued)
Interference Levels and Treatments
Collect samples in glass or plastic bottles and analyze 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 below 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 (Cat. No. 2450-53) to each liter (or quart) of sample, using a glass
serological pipet and pipet filler. Check the sample pH; 4-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 or sample distillation
procedures should be adjusted to approximately pH 7 with 2.5 N Hydrochloric Acid
Standard Solution. Where significant amounts of preservative are used, a volume
correction should be made; see Section 3.1.3 Correcting for Volume Additions on page
29.
Oxidizing Agents
Oxidizing agents such as chlorine decompose cyanides during storage. To test
for their presence and to eliminate their effect, pretreat the sample as follows:
a. Take a 25-mL portion of the sample and add one drop of 10-g/L
m-Nitrophenol Indicator Solution (Cat. No. 2476-32). Swirl to mix.
b. Add 2.5 N Hydrochloric Acid Standard Solution drop-wise until the
color changes from yellow to colorless. Swirl the sample thoroughly after
the addition of each drop.
c. Add two drops of Potassium Iodide Solution, 30-g/L (Cat. No. 343-32),
and two drops of Starch Indicator Solution, to the sample. Swirl to mix.
The solution will turn blue if oxidizing agents are present.
Cyanide_PP_Other_PPZ_Eng_Ody.fm
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