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Measurement and Results - Poor lithium (Li) precision with new ICP-OES
My lab is having trouble with precision on our ICP for Lithium analysis. We are analyzing radioactive liquid samples in a boron matrix for lithium, aluminum, calcium, copper, iron, magnesium, potassium, zinc and nickel. Our old instrument was setup to analyze at the 610nm wavelength due to oversaturation in the PPM range. We purchased a new ICP-OES but my supervisors are still insisting on the 610nm line, even though we now have the ability to do 670 radial or axial. Also, our repeatability with the new instrument/method is questionable at best, hardly to 2 decimal places even in the PPM range.
I was reading the Lithium sample preparation article and I noticed that entrained gasses may bubble out in the nebulizer causing issues. Our system has about 30% dissolved hydrogen. We have a Miramist nebulizer, but I can't find any info about gas being a problem.
Any suggestions would be appreciated.
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admin
Total posts: 529
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If the precision of your Li measurements was satisfactory prior to using the new OES, and your samples have not changed significantly, then this would suggest that the new sample introduction system is the dominant variable affecting your repeatability. Generally speaking, precision variability between different emission lines would be a spectroscopic issue (e.g., due to interferences), and if the same poor precision is observed for multiple lines then the sample introduction system tends to be the likely culprit. If it’s possible to simply degas the samples by heating that would be a quick test of the influence of the dissolved hydrogen on the observed precision. Burgener Research offers a number of tips for optimizing Mira Mist nebulizers (http://www.burgener.com/MiraMistManual.html), and some of this advice might address the issues you are observing. As for the best Li line, we’d support a data-driven approach that includes careful examination of the spectra, comparison of axial vs. radial, and perhaps the evaluation of using an ionization buffer such as Cs to stabilize the ionization of Li. |