Why are low recoveries obtained when distilling cyanide standards with the MICRO DIST® cyanide distillation?

Document ID

Document ID TE8955

Version

Version 3.0

Status

Status Published

Published Date

Published Date 06/19/2018
Question
Why are low recoveries obtained when distilling cyanide standards with the MICRO DIST® cyanide distillation?
Summary
Low recoveries for cyanide distillation
Answer
If the MICRO DIST® tubes are not completely inserted into the heating block it is possible to get low recoveries. 

Low recoveries can also be obtained due to the pH of the samples and/or standards. If the pH is too high, the releasing solution added may not sufficiently acidify the sample. A low pH is necessary to convert cyanides to HCN (hydrogen cyanide). Depending on the initial pH and amount of hydroxide in the standard/sample, some additional sulfuric acid may be needed.


If standards and/or samples are preserved they should be raised to a pH of greater than 12 to preserve them. Too much hydroxide can prevent the releasing acid from acidifying the sample enough to release HCN.
 

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