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Will I lose analytes when my sample vents?

October 24, 2016

No, not under normal controlled conditions.

During a digestion a little bit of venting is totally normal and not harmful to your sample. In a typical digestion of an organic sample using nitric acid (organic samples tend to result in the most venting), the acid and sample in the closed vessel gradually heat up to the desired temperature. Thanks to the closed vessel we can achieve temperatures well above the normal temperatures capable in open vessel digestions which increases the oxidative potential allowing a more rapid and complete digestion of your sample. As temperature increases the pressure in the vessel increases. This pressure increase is a result of the vapor pressure of your acid as well as the formation of gaseous substances (in this case carbon dioxide). Once this pressure gets to the maximum operating pressure for the vessel, the vessel will lightly vent. It is primarily carbon dioxide with a small amount of acid vapor that is released. The vessel then reseals and the digestion continues to run unaffected. Your analytes are suspended in the acid within the vessel therefore not lost during venting. Excessive venting to the point of dryness would result in a loss but we prevent this by using an appropriate method for your acid and sample matrix. Holding at the appropriate temperature will avoid increasing the vapor pressure above the pressure specification of the vessel. Also, using the appropriate sample size will decrease the amount of carbon dioxide formed. One can visually see that there is little to no reduction in the volume within the vessel meaning nothing was lost.

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