Good morning, how are you doing?
There are several Fe, Mn, Ti, and W lines near the Si I 251.611 line. Consider running pure Fe to see if you have interference. Also try to use the same line used on the Spark OES (most often Si 288).
Make sure your calibration standards are made up in an Fe matrix.
Below is one of my favourite web pages:
and a link to the specific information for Si and interferences around it:
Also remember that perchloric acid is able to drive off silica. Be careful with this stuff - it has the tendency to cause explosions years after you used it.
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From: PLASMACHEM-L: Analytical Chem.(ICP's, DCP's, MIP's). [mailto:[log in to unmask]] On Behalf Of Linda Upp
Sent: Wednesday, 02 May 2018 00:02
To: [log in to unmask]
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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