How should samples be pretreated to avoid nitrate/nitrite interference for cyanide analysis using the Micro Dist©?

Document ID

Document ID TE8482

Version

Version 4.0

Status

Status Published

Published Date

Published Date 09/19/2018
Question
How should samples be pretreated to avoid nitrate/nitrite interference for cyanide analysis using the Micro Dist©?
Summary
Cyanide pretreatment for nitrate and nitrite interference
 
Answer
High cyanide results may be obtained for samples that contain nitrate and/or nitrite. During the distillation, nitrate and nitrite will form nitrous acid, which will react with some organic compounds to form oximes. These compounds, once formed, will decompose under test conditions to generate HCN. The possibility of interference of nitrate and nitrite is eliminated by pretreatment with sulfamic acid just before distillation.

Standard Methods recommends adding 2 grams of sulfamic acid to 500 mL of sample for macro distillation. This can be scaled down to accommodate the smaller volumes used in the cyanide Micro Dist© procedure. For example, 0.40 grams of sulfamic acid can be added to 100 mL of sample and dissolved by stirring prior to using a 6 mL aliquot for distillation. Alternatively, 24 milligrams of sulfamic acid can be added directly to the Micro Dist© sample tube, in addition to 6 mL of sample, prior to distillation. It is recommended to verify this procedure by spiking cyanide standards with known concentrations of nitrate or nitrite.

Are manuals available for the Micro Dist© distillation block?

 

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