What could be causing poor recoveries from a MICRO DIST® distillation?

Document ID

Document ID TE1103

Version

Version 3.0

Status

Status Published

Published Date

Published Date 06/19/2018
Question
What could be causing poor recoveries from a MICRO DIST® distillation?
Summary
Poor recoveries from 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. Because the distillation process is pH dependent, it is important that the correct concentrations of acids and bases are always used. If samples are not buffered to the correct pH, they may not distill completely. Likewise, if the trapping solution is the wrong pH, then the distillate will not be fully recovered. Verify the reagent formulations for the solutions and verify that the sample is being brought to the correct pH for the test.

 

For example, when performing distillations for cyanide, 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. However, too much hydroxide can prevent the releasing acid from acidifying the sample enough to release HCN.

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