Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 156

Fig. 2.20 Apparatus used to isolate and concentrate molecular hydrogen
cyanide by the diffusion procedure
Source: Reproduced with permission from the American Chemical
Society [246]
Air purge method
The method for determining hydrogen cyanide uses a gas regulator and flow meter, a
temperature regulated sparging chamber and a glass bubbler through which finely
dispersed air is bubbled at 25-300ml min −1 into 20L of test solution. A glass bead
concentration column coated with about 0.4ml of 1.0N sodium hydroxide is used to
collect the displaced hydrogen cyanide and a water displacement bottle measures the
volume of air dispersed in the sample and passed through the column. At the end of the
collection period the cyanide absorbed in the concentration column is washed off with
three 5ml washings of deionised water into a 25ml volumetric flask for colorimetric
analysis.
The hydrogen cyanide concentration in a solution is calculated from the quantity of
hydrogen cyanide collected in a column and by reference to a calibration curve relating
the micrograms of hydrogen cyanide displaced per litre of air dispersed with the known
hydrogen cyanide concentration in standard solutions of the same temperature.
Diffusion method
The apparatus used to determine hydrogen cyanide by the diffusion method consists of a
2.8L Fernbach flask (Corning 4420) fitted with an airtight No 13 neoprene rubber stopper
and the bottom section of a petri dish (Corning 3160, 60×15 mm) attached by silicone