Measuring trace elements using multi standard calibration

[John Donovan]

On a related note, I have a set of reference materials covering a range of concentrations for my trace element. I want to use these to do calibration curve quantification (ideally quant mapping). How do I do this? I've found discussions and guides for calibrating the MAN background but this isn't the mode I want.

Hi Mike,
You'll want to do this from Probe for EPMA of course, but the multi-standard calibration curve method is very easy.

Once you've acquired your calibration standards (using off-peaks or not, just be self consistent), select the matrix correction methods dialog from the Analytical menu as seen here:



Then select this option here:



You can graphically plot your standard calibration along with the interpolated unknown calculated background from the Run | Display Calibration Curve Intensities menu as seen here:



Here's an example (not really intended for a calibration curve but you get the idea):

[Mike Matthews]

Thanks John,

Do I need to specify the standard calibrations as being a calibration curve set? I'll have another look but I couldn't see how to calibrate without having to specify a background of some sort.

[John Donovan]

Do I need to specify the standard calibrations as being a calibration curve set? I'll have another look but I couldn't see how to calibrate without having to specify a background of some sort.

So you can use any background type but you should use the same background type for your standards and your unknowns.

For instance generally you would just do off-peak bgds on both, and if you do you get an extra benefit in that you can (from the Analysis Options dialog) specify to add a 0,0 (synthetic) intensity versus concentration point to help the fit.

If you decide to save time you can specify using both MAN backgrounds for the stds and unks, but then you cannot add a synthetic 0,0 point into the fit, because then zero concentration won't have a zero intensity.

Either way, once you select multi-standard calibration curve it will figure out the rest automatically- no need to even assign standards!

[Mike Matthews]

One of the benefits of a calibration curve is that you don't need to measure backgrounds at all, it just gives you a direct correlation between measured counts (peak+background) and weight percent element. Does PfE allow me to calibrate my standards with no background positions?

[John Donovan]

One of the benefits of a calibration curve is that you don't need to measure backgrounds at all, it just gives you a direct correlation between measured counts (peak+background) and weight percent element. Does PfE allow me to calibrate my standards with no background positions?

Yes. That's exactly what I'm saying!

Select the MAN background acquisition method in Acquire! | Acquisition Options dialog, and the app won't acquire any off-peak intensities. 

Normally one would *also* acquire some MAN (on-peak only) intensities on some standards that *do not* contain the element(s) of interest to get a proper background correction (good to ~a few hundred PPM), but since you'll be selecting the multi-standard calibration curve method you won't have to.

Does this make sense?

My previous post point was: just be sure to use the same background acquisition method for both your standards and your unknowns within a probe run for the multi-standard calibration curve method.

[Mike Matthews]

Ah, OK, I see what you're saying now. I thought that if I used the MAN setting it would use my standard measurements to generate a background correction curve rather than the element correlation. I'll give it a try when I get back in after Easter.