Hi Jakub,

As you know the idea of the quantitative spectral interference correction is to correct for the differences in the matrix correction between the standard used for the interference correction and the sample being measured. Since the standard used for the interference correction must contain a known amount of the interfering element, *and* none of the interfered element, *nor* any other elements interfering with the element of interest, they are likely to be compositionally different. In fact, since we generally prefer an interference standard which contains a high concentration of the interfering element (for best precision), this is usually the case. Though not always!

But there's a trick we use in the spectral interference correction code to make the matrix correction of these obscure interfering emission lines much easier.

Because any photons from any interfering emission lines are being detected by the same spectrometer (which is already tuned to one of the major lines of interest that we are measuring), we can make an assumption (at least for the case of first order emission lines causing the interference), that the photon energy is the same as the emission line that is being interfered with.

Therefore we might assume that we can apply the same matrix correction (for the line being measured), to the line causing the interference. However, this assumption breaks down if spectral interference is caused by a higher order reflection. In these cases, the photon energy of the interfering line is at least twice the energy of the line being observed, so in these cases we simply skip the matrix correction and just utilize the concentration ratios without a matrix correction, as suggested in our original paper. The justification being that a high energy emission line has a small matrix correction, and is therefore close to unity.

You can see that (if you had PfE), by running the software in "Verbose Mode" and looking at the output as shown in this post:

https://probesoftware.com/smf/index.php?topic=626.msg8020#msg8020The other assumption is that the fluorescence effects are the same for the measured line and the line causing the interference in the interference standard and the sample. For K edge fluorescences this is going to a reasonable assumption, but it starts to break down for L and M edges. So this assumption is at least approximately the case, but to be absolutely rigorous, we should perform the full matrix correction of each interfering emission line, which as you point out, would be a lot of work!

As you know, CalcZAF only calculates matrix corrections for 12 different emission lines (Ka, Kb, La, Lb, Ma, Mb, Ln, Lg, Lv, Ll, Mg, Mz), so for those really obscure lines, this is going to be difficult. For the example you mentioned of Y LG3 interfering with Pb Ma, the Y LG3 line is a first order reflection, so you are good to go with the assumption that the matrix correction for Y LG3 is approximately the same as for Pb Ma.

In fact, we have not observed cases where the simplifying assumptions made above caused any problems, but we would be interested in learning of such cases if you come across any.

john