Author Topic: Using Duplicate Elements in Probe for EPMA  (Read 3687 times)

Probeman

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Using Duplicate Elements in Probe for EPMA
« on: January 23, 2014, 02:59:35 pm »
One of the cool features in Probe for EPMA is that the program can properly handle the presence of "duplicate" elements for fully quantitative analysis.

This feature is often utilized with the "aggregate" mode,  for increasing the "geometric efficiency" of the instrument by combining photons (in software!) from different spectrometers to improve sensitivity. Note however, for this "aggregate" mode, the software will only combine photons from elements that utilize the *same* x-ray emission line! Why?  Because the physics doesn't care about the analyzing crystals used (photons is photons!), but the photon energies are very important for the physics, so they cannot be combined at the photon level.

Of course one might also just want some replicate measurements on multiple spectrometers without combining them using "aggregate" mode. If these are trace elements they will not affect the matrix correction enough to matter so that is fine.  But if the concentrations of the duplicate elements are large enough, the matrix correction will be adversely affected.

Let's look at an example of this, using some GaAs and GaSb synthetic standards. Here is the output from the analysis of GaSb:

St  669 Set   2 GaSb (synthetic)
TakeOff = 40.0  KiloVolt = 20.0  Beam Current = 20.0  Beam Size =   10
(Magnification (analytical) =  40000),        Beam Mode = Analog  Spot
(Magnification (default) =      400, Magnification (imaging) =    800)
Image Shift (X,Y):                                          .00,   .00

(MAC block)
Number of Data Lines:   5             Number of 'Good' Data Lines:   5
First/Last Date-Time: 01/07/2014 05:39:27 PM to 01/07/2014 05:47:40 PM
WARNING- Using Exponential Off-Peak correction for as ka
WARNING- Using Exponential Off-Peak correction for sb la

Average Total Oxygen:         .000     Average Total Weight%:  154.313
Average Calculated Oxygen:    .000     Average Atomic Number:   39.191
Average Excess Oxygen:        .000     Average Atomic Weight:   84.510
Average ZAF Iteration:        5.00     Average Quant Iterate:     2.00
WARNING- Duplicate analyzed elements are present in the sample matrix!!
Use Aggregate Intensity option or Disable Quant feature for accurate matrix correction.

St  669 Set   2 GaSb (synthetic), Results in Elemental Weight Percents
 
ELEM:       Ga      Ga      Ga      As      In      Sb
BGDS:      LIN     LIN     LIN     EXP     LIN     EXP
TIME:    60.00   60.00   60.00   60.00   30.00   30.00
BEAM:    19.94   19.94   19.94   19.94   19.94   19.94

ELEM:       Ga      Ga      Ga      As      In      Sb   SUM 
XRAY:     (la)    (ka)    (la)    (ka)    (la)    (la)
   137  28.309  34.369  28.601   -.038   -.059  63.473 154.656
   138  28.262  34.325  28.414   -.144   -.040  63.320 154.137
   139  28.303  34.444  28.558   -.097   -.070  63.177 154.315
   140  28.363  34.395  28.473   -.038   -.096  63.243 154.339
   141  28.368  34.292  28.484   -.080   -.051  63.107 154.120

AVER:   28.321  34.365  28.506   -.079   -.063  63.264 154.313
SDEV:     .044    .059    .074    .044    .022    .141    .216
SERR:     .020    .026    .033    .020    .010    .063
%RSD:      .16     .17     .26  -55.91  -34.07     .22

PUBL:   36.413  36.413  36.413    n.a.    n.a.  63.587 100.000
%VAR:   -22.22   -5.62  -21.72     ---     ---  (-.51)
DIFF:   -8.092  -2.048  -7.907     ---     ---  (-.32)
STDS:      662     662     662     662    2002     669

STKF:    .4679   .5103   .4679   .4873   .5621   .5907
STCT:   648.92  694.60  232.91   91.23  200.87  236.11

UNKF:    .1403   .3532   .1413  -.0008  -.0006   .5906
UNCT:   194.62  480.73   70.31    -.15    -.21  236.09
UNBG:     2.62   12.42     .73    3.04    1.66    2.79

ZCOR:   2.0181   .9730  2.0181  1.0192  1.0841  1.0711
KRAW:    .2999   .6921   .3019  -.0016  -.0010  1.0000
PKBG:    75.25   39.72   97.62     .95     .88   85.59
INT%:     ----    ----    ----    ----    ----    ----


First note that we are acquiring Ga La on two spectrometers and Ga Ka on one spectrometer, plus As, In and Sb. GaSb is the primary standard for Sb and GaAs is the primary standard for Ga.

Next we note that the analysis is crazy.  The total is over 150% and we have three times as much Ga as we should... we makes sense because we are measuring Ga on three spectrometers!  So let's begin by turning on the "aggregate" mode in the Analytical | Analysis Options dialog as seen here:



Now we get this output when we click the Analyze button:

St  669 Set   2 GaSb (synthetic)
TakeOff = 40.0  KiloVolt = 20.0  Beam Current = 20.0  Beam Size =   10
(Magnification (analytical) =  40000),        Beam Mode = Analog  Spot
(Magnification (default) =      400, Magnification (imaging) =    800)
Image Shift (X,Y):                                          .00,   .00

(MAC block)
Number of Data Lines:   5             Number of 'Good' Data Lines:   5
First/Last Date-Time: 01/07/2014 05:39:27 PM to 01/07/2014 05:47:40 PM
WARNING- Using Exponential Off-Peak correction for as ka
WARNING- Using Exponential Off-Peak correction for sb la
WARNING- Using Aggregate Intensities for Duplicate Elements
Element ga la on channel 1(LTAP) is duplicated by ga la on channel 3(TAP)
Element ga la on channel 1(LTAP) is duplicated by ga la on channel 3(TAP)

Average Total Oxygen:         .000     Average Total Weight%:  129.446
Average Calculated Oxygen:    .000     Average Atomic Number:   40.787
Average Excess Oxygen:        .000     Average Atomic Weight:   88.152
Average ZAF Iteration:        5.00     Average Quant Iterate:     2.00

St  669 Set   2 GaSb (synthetic), Results in Elemental Weight Percents
 
ELEM:       Ga      Ga      Ga      As      In      Sb
BGDS:      LIN     LIN     LIN     EXP     LIN     EXP
TIME:    60.00   60.00     .00   60.00   30.00   30.00
BEAM:    19.94   19.94     .00   19.94   19.94   19.94
AGGR:        2                                       

ELEM:       Ga      Ga      Ga      As      In      Sb   SUM 
XRAY:     (la)    (ka)    (la)    (ka)    (la)    (la)
   137  31.221  34.985    .000   -.038   -.059  63.615 129.725
   138  31.123  34.941    .000   -.143   -.039  63.462 129.343
   139  31.202  35.062    .000   -.097   -.070  63.319 129.417
   140  31.220  35.011    .000   -.038   -.095  63.387 129.485
   141  31.233  34.907    .000   -.080   -.050  63.249 129.259

AVER:   31.200  34.981    .000   -.079   -.063  63.406 129.446
SDEV:     .044    .060    .000    .044    .021    .141    .177
SERR:     .020    .027    .000    .020    .010    .063
%RSD:      .14     .17     .09  -55.91  -34.07     .22

PUBL:   36.413  36.413    n.a.    n.a.    n.a.  63.587 100.000
%VAR:   -14.32   -3.93     .00     ---     ---  (-.28)
DIFF:   -5.213  -1.432     .00     ---     ---  (-.18)
STDS:      662     662       0     662    2002     669

STKF:    .4637   .5222   .0000   .4908   .5621   .5976
STCT:   881.83  694.60     .00   91.23  200.87  236.11

UNKF:    .1393   .3614   .1413  -.0008  -.0006   .5976
UNCT:   264.92  480.73     .00    -.15    -.21  236.09
UNBG:     3.35   12.42     .00    3.04    1.66    2.79

ZCOR:   2.2399   .9679  2.0181  1.0065  1.0729  1.0610
KRAW:    .3004   .6921   .3019  -.0016  -.0010  1.0000
PKBG:    80.05   39.72     .00     .95     .88   85.59
INT%:     ----    ----    ----    ----    ----    ----


This is a little better because the two Ga La channels have been "aggregated" as we specified, but we still have duplicate Ga La and Ga Ka.  What we need to do here is to "turn off" either the 2 Ga La channels or the single Ga Ka channel using the "Disable Quant" feature. 

Since the Ga La channels are being "aggregated" it is critically important to use the "Disable Quant" feature on *both* the standards *and* the unknowns.  Since this is a secondary standard for Ga, we would want to apply the "Disable Quant" flags to both the primary GaAs standard and the GaSb secondary standard.

Or we could just set the "Disable Quant" flag for *only* the Ga Ka channel in this standard sample as seen here:



since it is not duplicated as far as the "aggregate" mode is concerned.

Now, when we again click the Analyze button in the Analyze! window we obtain these reults:

St  669 Set   2 GaSb (synthetic)
TakeOff = 40.0  KiloVolt = 20.0  Beam Current = 20.0  Beam Size =   10
(Magnification (analytical) =  40000),        Beam Mode = Analog  Spot
(Magnification (default) =      400, Magnification (imaging) =    800)
Image Shift (X,Y):                                          .00,   .00

(MAC block)
Number of Data Lines:   5             Number of 'Good' Data Lines:   5
First/Last Date-Time: 01/07/2014 05:39:27 PM to 01/07/2014 05:47:40 PM
WARNING- Using Exponential Off-Peak correction for as ka
WARNING- Using Exponential Off-Peak correction for sb la
WARNING- Using Aggregate Intensities for Duplicate Elements
Element ga la on channel 1(LTAP) is duplicated by ga la on channel 3(TAP)
Element ga la on channel 1(LTAP) is duplicated by ga la on channel 3(TAP)
WARNING- Quantitation is Disabled For ga ka, Spectro 3

Average Total Oxygen:         .000     Average Total Weight%:   99.891
Average Calculated Oxygen:    .000     Average Atomic Number:   43.717
Average Excess Oxygen:        .000     Average Atomic Weight:   95.732
Average ZAF Iteration:        7.00     Average Quant Iterate:     2.00

St  669 Set   2 GaSb (synthetic), Results in Elemental Weight Percents
 
ELEM:       Ga      Ga      Ga      As      In      Sb
BGDS:      LIN     LIN     LIN     EXP     LIN     EXP
TIME:    60.00     ---     .00   60.00   30.00   30.00
BEAM:    19.94     ---     .00   19.94   19.94   19.94
AGGR:        2     ---                               

ELEM:       Ga    Ga-D      Ga      As      In      Sb   SUM 
XRAY:     (la)    (ka)    (la)    (ka)    (la)    (la)
   137  36.465     ---    .000   -.038   -.057  63.792 100.162
   138  36.363     ---    .000   -.142   -.039  63.634  99.817
   139  36.467     ---    .000   -.096   -.068  63.491  99.794
   140  36.475     ---    .000   -.037   -.094  63.562  99.905
   141  36.479     ---    .000   -.079   -.049  63.425  99.776

AVER:   36.450     ---    .000   -.078   -.061  63.581  99.891
SDEV:     .049     ---    .000    .044    .021    .141    .159
SERR:     .022     ---    .000    .020    .009    .063
%RSD:      .13     ---     .09  -55.91  -34.07     .22

PUBL:   36.413    n.a.    n.a.    n.a.    n.a.  63.587 100.000
%VAR:      .10     .00     .00     ---     ---  (-.01)
DIFF:     .037     .00     .00     ---     ---  (-.01)
STDS:      662     ---       0     662    2002     669

STKF:    .4557     ---   .0000   .4976   .5621   .6098
STCT:   881.83     ---     .00   91.23  200.87  236.11

UNKF:    .1369     ---   .0000  -.0008  -.0006   .6097
UNCT:   264.92     ---     .00    -.15    -.21  236.09
UNBG:     3.35     ---     .00    3.04    1.66    2.79

ZCOR:   2.6622     ---   .0000   .9833  1.0529  1.0428
KRAW:    .3004     ---   .0000  -.0016  -.0010  1.0000
PKBG:    80.05     ---     .00     .95     .88   85.59
INT%:     ----     ---    ----    ----    ----    ----


See the line above labeled VAR% which is the relative percent variance from the "published" value. Of course a relative accuracy of less than 1% is almost too good to be true, but we'll take it!  :-)

Especially since the matrix correction for Ga La in this standard is over 200%, so perhaps we ought to call it "spurious accuracy".
« Last Edit: January 24, 2014, 11:09:13 am by John Donovan »
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Probeman

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Re: Using Duplicate Elements in Probe for EPMA
« Reply #1 on: April 12, 2017, 08:29:54 am »
Here's an important tip on using the aggregate mode with duplicate elements:

The duplicate elements on your spectrometer/crystals that are aggregated for your unknowns, must match the duplicate elements on your spectrometer/crystals that are aggregated for your standards.

Why?  Because the intensities from each duplicate elements are summed for both the standards and the unknowns.  If they don't have the same geometry efficiency (intensity/area) then when the k-ratio is formed, it will not be accurate.

It would be like standardizing on one crystal/spectrometer combination and using a different spectrometer/crystal combination for the unknowns.  I thought about adding code to check that the user does this properly, throughout a run that could be any combination of duplicate elements/spectometers/crystals, but my brain exploded...  so I decided to leave responsibility for this to you, kind users.
john
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John Donovan

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Re: Using Duplicate Elements in Probe for EPMA
« Reply #2 on: December 29, 2019, 10:46:29 am »
I recently had a colleague of ours contact me because they were analyzing a trace element on several spectrometers to improve their sensitivity. That is, by improving the "geometric efficiency" of the instrument by tuning up the trace element on several spectrometers. Here is an example (posted above) of analyzing some duplicate major elements, which shows the issue more clearly:

https://probesoftware.com/smf/index.php?topic=155.msg646#msg646

However in examining their trace element data, they found that they needed to "disable quant" on one of the spectrometers for an electronic/mechanical reason, but when they disabled the quantification for that element/spectrometer, the k-ratio was no longer correct.

I wanted to recall this topic to remind everyone that because Probe for EPMA aggregates the intensities for *both* the unknowns *and* the standard samples (both are necessary to construct the k-ratio!), both the unknowns and the standards need to be treated the same. So if one disables an element in the unknown sample, one should also disable the quantification for the same element in the standard sample.

Now maybe a really smart developer would find a way to warn the user that the element /spectrometer for a particular unknown is disabled, but that the same element/spectrometer for the corresponding standard is not disabled, but it gets complicated let me assure you!  But we are thinking about how such a warning in the code could be implemented!

So in the meantime, if you decide you want to disable quantification for a particular duplicate element in an unknown sample, be sure to also disable the quantification for that same duplicate element in the standard samples.

The easiest way to do that is to simply click the "All Samples" option in the Analyze! window, then click the Select All button, then click the Elements/Cations button, then disable the quantification for the duplicate element as usual.
« Last Edit: December 29, 2019, 02:21:01 pm by John Donovan »
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