How do internal standards work and how do you choose the correct one?

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Lilly365's picture
How do internal standards work and how do you choose the correct one?


I just started to run an Optima 5300DV ICP-OES.  I have had very limited training,  as the individual who was doing this job retired and didn't want to be bothered with any important details or explanations. (Excessively stressful situation as a result!!!!!)   I just got a "push this and click on that" over view.

I do trace analysis on powdered metal. It is a 90-96% Fe base with trace amounts of Cu, Ni, Mn, Mo, P, Cr, Mg, V, Pb, Zn and B.

I see a great deal of interference from the Fe as well as Mo. And the Cu and P seem to interfere with each other as well.

I looked through the Winlab Help options and am going to try and use MSF for this.
Is it possible to correct for all these elements in one Method?
How would using an internal standard help, and how do I choose which element to use?
All the methods in the computer when I got here did NOT have an internal standard or a QC check. 

RyanATC's picture
 The fact that there was no

 The fact that there was no internal standard or QC check in place is a bit scary. Instituting both of those should definitely be your top priority!

As for a good internal standard to use, you want one that you are unlikely to test for, is stable in solution, is not likely to be found naturally in your samples, is chemically compatible, and doesn't interfere with any of your analytes. One of the most commonly used is yttrium, as it tends to meet these requirements for most tests. The internal standard acts as a base point to compare your results to. It helps compensate for changes in the instrument - such as intensity drift - and small natural errors in dilutions. 

As for your elemental interferences, the easiest correction there is to select different wavelengths for the elements causing the interference. For example, my most common test includes both Cu and P and we changed wavelengths to prevent the interference. We use Cu 327.395 and P 213.618. As for the Fe and Mo, I'm not aware of any significant overlap between them, but there should be some other useable wavelengths there as well.