Variable Step Size (during WS)

[Rom]

Hi, could you explain how I can choose count time for integrated intensity scans.

In "Count time" of Acquire! note: "on-peak count time for integrated intensity scans are the total time for the full element scan". But time diagram shows something else.

So, how "On-Peak time" and "off Peak time" affect time of integrated intensity scans?
Thank you.

[Probeman]

The integrated intensity acquisition for standard and unknowns is usually only applied to low energy emission lines to account for peak shift and/or shape changes due to chemical bonding and site coordination. The method works well for this, but does require considerable additional acquisition time.   Please note one must acquire integrated intensities for both standard and unknown samples for proper quantification.

The other method to account for peak shift and/or shape changes is to perform normal peak acquisitions and account for these peak shift or shape changes using specified or compound APFs (area peak factors).  See the Reference Manual for more information.
 
However, it's not easy to estimate the total acquisition time for integrated intensity scans because it depends on the measured intensities of the standard or unknown. That is, the step size used for each point acquisition in the scan depends on the square root of the peak intensity, so it cannot be predicted exactly. In other words, the higher the peak intensity the smaller the step size for each scan point.

This variable step size is used to increase the precision of the scan for the peak intensities as opposed to the background intensities since the peak is what is most important for quantification.  However, one can also set the Initial Step Size and the Minimum Step Size equal to each other to have a constant step size.

Regarding the background acquisition, it is the same as for normal standards and unknowns.

See the Reference Manual and search for Integrated Intensity Options.

[Rom]

It is clear, thanks. How I can see and change count time for each spectrometer position during the integrated intensity scan?

[Probeman]

It is clear, thanks. How I can see and change count time for each spectrometer position during the integrated intensity scan?

The count time per scan point should be the on-peak count time (displayed in the Count Times dialog), but one cannot change the acquisition parameters during the acquisition.

[Rom]

Could you share with me some tricks which will help to measure  integrated intensity (and APF as well) for peaks contain an extra one.
For instance, ka oxygen peak includes small Si peak on SiO2. So how I can ignore this small peak because background level is lower then "hight off-peak" of this small peak.
We use LDE, JEOL.
See addition.
Thank you

[Probeman]

Could you share with me some tricks which will help to measure  integrated intensity (and APF as well) for peaks contain an extra one.
For instance, ka oxygen peak includes small Si peak on SiO2. So how I can ignore this small peak because background level is lower then "hight off-peak" of this small peak.
We use LDE, JEOL.
See addition.
Thank you

Rom,
I think you are confusing two different things.

When using the integrated intensity feature for quantitative analysis, the peak shift and/or shape changes are automatically compensated for, because you are obtaining the integrated intensity of each peak. So there is no need to also utilize the area peak factor (APF) corrections. But you'll still need to deal with background and interference corrections.

If instead you want to use the APF corrections, simply utilize the normal on-peak/off-peak acquisitions and then select whether to utilize the compound APFs included with PFE, or (more work) measure the specified APFs for your specific unknown relative to your specific standard. The differences between compound APFs and specified APFs are discussed here:

https://probesoftware.com/smf/index.php?topic=536.0

However in both cases you will need to correct for, or avoid, spectral interferences. In the case of using integrated intensities you will need to identify the interfering peak, and then also acquire integrated intensities on an appropriate interference standard, and then assign the interference assignment as usual.

In the case of using normal on-peak/off-peak measurements and measuring a specified APF for your unknown, you would have to deconvolve the interfering peak(s) from both your unknown and standard integrated intensity scans to obtain an interference corrected specified APF, and then you would have to apply an interference correction as usual to the actual unknowns (and standard). 

However, it should be noted that because the integrated intensity scans are a much wider spectral area (than simply measuring the on-peak intensity), you are much more likely to have spectral interferences with integrated intensity scans. Note also that you must avoid off-peak spectral interferences in both cases, but that is relatively easy to do because one can select different background measurement positions. 

With all this in mind, I suggest you are probably better off using normal on-peak/off-peak measurements and the compound APFs that are already included in PFE. Also be sure to use a suitable background correction, e.g, an exponential or MPB background method to obtain properly corrected net intensities.

And of course after all that, one also has to consider the accuracy of the mass absorption coefficients (MAC) for low energy emission line measurements. But that is another topic!

In the meantime here are a number of "white papers" from many years ago which discusses some of these APF issues:

https://epmalab.uoregon.edu/reports/APF%20measurements.doc

https://epmalab.uoregon.edu/reports/APF%20Normalization.pdf

https://epmalab.uoregon.edu/reports/Withers%20hydrous%20glass.pdf

https://epmalab.uoregon.edu/reports/Preliminary%20work%20on%20MgB2%20and%20MgB4.pdf

Of course the easy way to handle these peak shape/shift issues is to use a matrix matched standard for your unknown, but that is not always possible.

[Rom]

Thank you for materials and explanations.
In other words if we have an interfering peak(s) inside our scanning area we should use procedure of interfering correction. This procedure is the same like we use in normal on-peak/off-peak measurements. Of course, all measurements should be done in "integrated intensity feature".
Am I right?

[Probeman]

Thank you for materials and explanations.
In other words if we have an interfering peak(s) inside our scanning area we should use procedure of interfering correction. This procedure is the same like we use in normal on-peak/off-peak measurements. Of course, all measurements should be done in "integrated intensity feature".
Am I right?

I haven't tried this myself, but I think it should work.  Perhaps first give it a try using a standard acquired as an unknown. Yes, all (both the interfered and the interfering element) must use integrated intensities for acquisition. 

The background placements (as well as the background fit model) will be very important.  That is, the off-peak measurement positions must avoid any spectral interferences.

[Rom]

Will try.
Thank you again.