Application Note Cyanide

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Vapodest 20S Rapid Steam Distillation Unit

In general Cyanide is generally liberated from a sample by acidification to form HCN then distilled. The HCN is captured by a weak solution of NaOH then analysed for CN content. Samples will normally be " fixed " on site by the sampler by the addition of one or two pellets of Sodium Hydroxide.

Several different methods are used for Cyanide determination. All methods have been developed using the Gerhardt Vapodest distillation units. The Vapodest can be programmed to acidify the sample and distil for normally 3 to 4 minutes as opposed to 30 – 40 minutes on a traditional distillation apparatus.

Samples are compared to a standard reference solution of Potassium Cyanide. Reference concentrations should be freshly prepared for each batch, dependant on the levels to be detected.

Total Cyanide is determined by the distillation of the acidified sample in the presence of Copper Chloride and collecting the distilled HCN in alkali.

The liberated CN is estimated colormetrically using Chloramine -T, Pyridine and Barbituric acid. The purple colour formed absorbs at 578nm and is measured in a spectrophotometer.

Alkali Extractable Cyanide

To extract the cyanide present in alkali and then to determine the quantity via distillation and colourmetric end point.

Sample is placed into a bottle NaOH added and shaken for 1 hour. When finished the contents are filtered. The solution is then distilled in the presence of Copper Chloride and the HCN captured in alkali as above.

The liberated CN is estimated colormetrically using Chloramine -T, Pyridine and Barbituric acid. The purple colour formed absorbs at 578nm and is measured in a spectrophotometer.

Free Cyanide

Free Cyanide may be determined on clean, colourless samples without distillation.

The Vapodest unit may be used to clean up a coloured or cloudy sample by distilling prior to colouration using Chloramine - T, pyridine and barbituric acid. The purple colour formed absorbs at 578nm and is measured in a spectrophotometer.

Hazards

It is recommended that all operations involving Cyanide distillations, pH correction and colour production are carried out inside a fume cupboard

For more information on Gerhardt Rapid Distillation Units Vapodest – click here.

For more information on Gerhardt Traditional Distillation Equipment – click here.