Preparation of Reagents and Cyanide Standards All reagents shall conform to the reagent grade specifications of the American Chemical Society (ACS). Other grades may be used provided they are of sufficiently high purity to ensure high accuracy of the determination. Refer to the listing of the chemicals used and the suppliers given in Appendix C. Solid and liquid reagents must be carefully and accurately prepared (Fig. 3) as described below. 11.1 Sodium Hydroxide Solution (for Absorber Tube) Dissolve 40 grams of sodium hydroxide pellets in distilled water (glass distillation not copper distillation apparatus) and dilute to one liter in a volumetric flask. This is equivalent to a one Molar NaOH solution. 11.2 Sodium Hydroxide Diluent Dissolve 1.6 grams of sodium hydroxide pellets in distilled water and dilute to one liter in a volumetric flask. This is equivalent to approximately 0.04 Molar NaOH solution. 7 Figure 2. Protective clothing worn by laboratory technician working with cyanide. 11.3 Ionic Strength Adjustor (10 M NaOH) Dissolve 40 grams of NaOH pellets in distilled water and bring to volume in a 100 ml volumetric flask using distilled water. Filter the solution through glass wool and transfer it to a polyethylene container. Caution: Heat is given off during mixing. Prepare an ice water bath to cool the solution. 11.4 Magnesium Chloride Solution Dissolve 510 grams of magnesium chloride hexahydrate in distilled water and dilute to one liter in a volumetric flask. 11.5 Sulfuric Acid Solution (1:1) Slowly add 250 ml of concentrated sulfuric acid to 100 ml of distilled water in a 500 ml using a volumetric flask. Dilute the solution to the 500 ml mark with distilled (or deionized) water. Caution: Heat is produced during mixing. Hence, the flask should be cooled in a bath of ice water. Progressively dilute the solution with distilled water to allow it to cool to near room temperature (about 20o C). The final 500 ml volume should be the volume read on the flask at room temperature, since heated solutions tend to expand. 8 Figure 3. Chemist preparing standard solutions from solid reagents in the CDT laboratory. 11.6 Sulfamic Acid Solution Dissolve 133 grams of sulfamic acid in distilled water and dilute to a volume of one liter in a volumetric flask. 11.7 Cyanide Stock Solution (1000 mg/L) Weigh out exactly 1.8846 grams of reagent grade NaCN crystals Dissolve the crystals in 4 ml ISA and bring the volume to one liter using distilled water. Store this stock solution in a well-sealed flask in a dark cabinet. Use the stock solution to prepare the cyanide standard solutions needed for the calibration. Prepare fresh stock solution every month. 11.8 100 mg/L Cyanide Standard a) Use a rubber bulb on a pipette or a metered pipetting device under the fume hood to remove 10 ml of the 1000 mg/L stock solution and add 1 ml of ISA (10 Molar NaOH). Then dilute the mixture to 100 ml using distilled or deionized water. b) Use the 100 mg/L solution to prepare the following standard solutions. 9 11.9 10 mg/L CN Solution-Pipette 10 ml of 100 mg/L CN- solution, add 1 ml ISA and dilute to 100 ml using distilled water. 11.10 1 mg/L CN- Solution-Pipette 10 ml of 10 mg/L CN solution, then add 1 ml ISA and dilute to 100 ml using distilled water. 11.11 0.1 mg/L CN- Solution-Pipette 10 ml of 1 mg/L CN solution, then add 1 ml ISA and dilute to 100 ml using distilled water. 11.12 0.05 mg/L CN- Solution-Pipette 50 ml of 0.1 mg/L , then add 1 ml ISA and dilute to 100 ml using distilled water. Note: It is necessary to carry out these procedures precisely using calibrated pipettes and volumetric flasks. 11.13 Store the cyanide standard solutions in amber-colored seale

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