Hach DR/850 Procedures Manual page 160

CYANIDE,
continued
Method Performance
Interferences
Immediately before use, prepare a 0.10 mg/L cyanide working
solution by diluting 1.00 mL of the 100 mg/L stock solution to
1000 mL using deionized water. Use this prepared standard in
place of sample in Step 3. Results should be 0.10 mg/L CN
Precision
In a single laboratory, using a standard solution of 0.19 mg/L CN
and two representative lots of reagent with the instrument, a single
operator obtained a standard deviation of ±0.017 mg/L CN
Estimated Detection Limit (EDL)
The estimated detection limit for program 23 is 0.008 mg/L CN.
For more information on the estimated detection limit, see
Section 1.
Turbidity
Large amounts of turbidity will interfere and cause high readings.
If the water sample is highly turbid, it should first be filtered
before use in Steps 3 and 12. Filter using the labware listed under
Optional Apparatus. The test results should then be recorded as
soluble cyanide.
Oxidizing and Reducing Agents
Large amounts of chlorine in the sample will cause a milky white
precipitate after the addition of the CyaniVer 5 Reagent. If
chlorine or other oxidizing agents are known to be present, or if
reducing agents (such as sulfide or sulfur dioxide) are known to
be present, use adequate ventilation and pretreat the sample
before testing as follows:
Oxidizing Agents
a) Adjust a 25-mL portion of the alkaline sample to between
pH 7 and 9 with 2.5 N Hydrochloric Acid Standard
Solution. Count the number of drops of acid added.
b) Add two drops of Potassium Iodide Solution and two
drops of Starch Indicator Solution to the sample. Swirl to
mix. The sample will turn blue if oxidizing agents are
present.
160
– .
-
- .