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Measurement and Results - High As and Se recoveries on ghost wipes

 
We have recently been getting elevated results for selenium and arsenic in our wipe quality control matrix spikes. We are using ghost wipes by and a hot acid digestion using concentrated nitric acid. We have started getting recoveries of upwards of 150%. Historically we have had high recoveries from these two elements. I was wondering if you would be able to provide any insight as to why these recoveries are so high. Thank you very much.
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admin Total posts: 529

Are you running these elements by ICP-MS?  If so, this sounds like you may be getting significant chloride contamination that could be affecting your results for As and Se.  Those elements have direct Ar-Cl interferences that could account for your high recoveries.

Posted: 09/05/18 20:37:42
admin Total posts: 529

Are you running these elements by ICP-MS?  If so, this sounds like you may be getting significant chloride contamination that could be affecting your results for As and Se.  Those elements have direct Ar-Cl interferences that could account for your high recoveries.

Posted: 09/05/18 20:37:42
admin Total posts: 529

It’s possible that the elevated levels of As and Se that you are seeing are due to a presence of some kind of carbon containing molecule.  Carbon (usually in the form of methanol) is sometimes added to ICP solutions to allow poorly ionized elements to ionize more readily, thus resulting in higher intensities.  This would actually be an ideal technique for As and Se.  The carbon could be a new contaminant present in the wipes that is causing your As and Se to ionize more readily now than in the past.  Do you see a significant increase in carbon intensities when testing the wipe QC matrix spikes compared to other samples being run?  Do you use any internal standards or ionization buffers, such as 500ppm Cs?  Are all wavelengths for As and Se showing an increase in intensity?

Posted: 09/05/18 20:29:13

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