251 should be a safe wavelength for Si in steels. I would second George's advice in re the acid rinse and addition of HF, especially for Nb. The interactive periodic table below is quite informative for chemical compatibility, stability, and sample prep for each element:
Glass Expansion Inc.
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From: PLASMACHEM-L: Analytical Chem.(ICP's, DCP's, MIP's). <[log in to unmask]> On Behalf Of George Glavin
Sent: Tuesday, May 1, 2018 10:25 AM
To: [log in to unmask]
Subject: Re: high bias on silicon, low niobium
Try using acid for rinsing between the samples (same concentration as in the samples). Without HF Si is likely to be in the form of somewhat volatile silicic acid (I am sure the exact chemistry is more complex) - when you switch from water to acid you get a transient spike of silicon signal that may affect your results. Silicon at 251.6 should not have much spectral interference from steel matrix (although I have seen some order overlap on some Echelle spectrometers) To improve Nb recovery, you may need to add HF - this would require HF resistant sample introduction system and torch of course.
Saint-Gobain Northboro R&D Center
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On Tuesday, May 1, 2018, 10:02 AM, Linda Upp <[log in to unmask]> wrote:
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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