Hach DR/700 Procedures Manual page 575

CYANIDE,
Prepare a 100 mg/L cyanide stock solution weekly by dissolving 0.1884
grams of sodium cyanide in 10 mL of 5.0 N sodium hydroxide and
diluting to 1000 mL with demineralized water.
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
demineralized water.
STATISTICAL EVALUATION
A single operator repetitively tested samples of two laboratory prepared
solutions, using one DR/700, matched sample cells and two
representative lots of reagent. Testing 0.098 mg/L CN
solutions, the standard deviation was ±0.0028 mg/L CN
Testing zero concentration samples, the limit of detection was
-
0.0011 mg/L CN
the standard deviation when testing zero concentration samples (adapted
from Analytical Chemistry, 1980, 52, 2242-2249).
INTERFERENCES
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 1 and 13. Filter using the labware listed under Optional
Apparatus. Record the test results 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, pretreat the
sample before testing as follows using adequate ventilation:
Oxidizing Agents
a) Adjust a 25-mL portion of the alkaline sample to pH 7-9 with 2.5 N
Hydrochloric Acid Standard Solution. Count the number of drops of
acid added.
b) Add 2 drops of Potassium Iodide Solution and 2 drops of Starch
Indicator Solution to the sample. Swirl to mix. The sample will turn
blue if oxidizing agents are present.
continued
. The limit of detection was calculated as three times
61-19
-
concentration
-
.