It is a long time since I did any OES so I'm not able to comment on the 251.6 nm performance of your instrument but in terms of your niobium have you considered that this might be a problem with acid hydrolysis? This is quite common in rock geochemistry. In acidic solutions the high field strength elements, like niobium, hydrolyse and can be lost from solution. There are different ways to deal with this, one of which is to complex the metal to keep it in solution. I know in the past that geochemists would use citric or tartaric acid to 'hold' the HFS elements in solution and avoid the problem of hydrolysis.
Just a thought.
Dr William Perkins
Reader in Geochemistry
Department of Geography and Earth Sciences
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From: PLASMACHEM-L: Analytical Chem.(ICP's, DCP's, MIP's). <[log in to unmask]> On Behalf Of Linda Upp
Sent: 01 May 2018 15:02
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Subject: high bias on silicon, low niobium
Got a question for the group. Here at AK we frequently will run a carbon or stainless steel by ICP, OES, and XRF - then compare the results from all three instruments to each other. My silicon is pretty much always running higher than that found by the other two methods. I'm using the
251.6 wavelength, and my background / baseline look good. My matrix varies from nitric, perchloric, or aqua regia most often, depending on which of the types of steel I'm doing. I always run NIST or ARMI certified standards at the same time, and will 'correct' to these certified materials if the results do not fall within expected limits.
(meaning if my Nickel is slightly low, I multiply results by the factor necessary to bring it in). I wouldn't anticipate that with these acids my torch would be dissolving into the matrix and contaminating my samples. By the time I run my acid concentration is around 10-20%, and I'm rinsing with water in between. I'm not sure if there's something I'm missing, but I thought I'd poll the community for thoughts.
Likewise, my niobium is frequently low - or missing altogether. I'm running this axially, and have just cleaned the window and aligned the torch. None of the niobium wavelengths are finding the niobium, which was present at about .01% in the recent round of proficiency samples.
I'd appreciate any advise / insights / etc on what I can do to improve these results.
As always, many thanks!
Linda S. Upp
AK Steel, Middletown Research Lab
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