Trace element interpretation

[John Donovan]

This topic is for discussing trace element data interpretation which is often problematic.

To start I will discuss the trace elements in the RbTiOPO4 standard materials that Owen Neill, Brian Joy and I have been discussing recently in this topic:

http://probesoftware.com/smf/index.php?topic=301.msg4267#msg4267

Here for reference are the results I obtained from a quant measurement at 400 seconds on-peak and 400 seconds on the off-peaks:

Un    7 RbTiOPO4, Results in Elemental Weight Percents
 
ELEM:        K      Cs      Na      Ca      Mg      Rb      Ti       P       O
TYPE:     ANAL    ANAL    ANAL    ANAL    ANAL    SPEC    SPEC    SPEC    SPEC
BGDS:      LIN     EXP     EXP     LIN     LIN
TIME:   400.00  400.00  400.00  400.00  400.00     ---     ---     ---     ---
BEAM:   100.94  100.94  100.94  100.94  100.94     ---     ---     ---     ---

ELEM:        K      Cs      Na      Ca      Mg      Rb      Ti       P       O   SUM 
   360    .015    .013   -.014    .000   -.001  34.979  19.604  12.676  32.741 100.014
   361    .016    .012   -.016    .000   -.001  34.979  19.604  12.676  32.741 100.012
   362    .016    .015   -.012    .000    .000  34.979  19.604  12.676  32.741 100.019
   363    .015    .013   -.017    .000   -.002  34.979  19.604  12.676  32.741 100.010
   364    .016    .015   -.010    .000    .000  34.979  19.604  12.676  32.741 100.021
   365    .015    .013   -.012    .000    .000  34.979  19.604  12.676  32.741 100.017
   366    .016    .012   -.013    .000   -.001  34.979  19.604  12.676  32.741 100.014

AVER:     .016    .014   -.013    .000   -.001  34.979  19.604  12.676  32.741 100.015
SDEV:     .000    .001    .003    .000    .001    .000    .000    .000    .000    .004
SERR:     .000    .000    .001    .000    .000    .000    .000    .000    .000
%RSD:     2.86    9.44  -18.91  273.41  -74.31     .00     .00     .00     .00

I'll start with the Na because a negative result is almost always an off-peak interference. But how can we know that?  If we go into the PFE Elements/Cations dialog we can use the Hi and Lo off-peak interference buttons to calculate the nominal interferences for this element as seen here:



The text result are here:

Code: [Select]

For Na ka (hi-off),    TAP at  12.5222 angstroms( 48685.8), at an assumed concentration of 1 wt.%
  Interference by P  KA1      II    at  12.3180 ( 47890.8) =      5.4%
  Interference by P  KA2      II    at  12.3240 ( 47914.2) =      3.8%
  Interference by Ca SKB``    IV    at  12.3280 ( 47929.8) =       .2%
  Interference by Ca SKB^5    IV    at  12.3460 ( 47999.8) =       .5%
  Interference by Ca KB3      IV    at  12.3610 ( 48058.2) =      6.6%
  Interference by Ca KB1      IV    at  12.3610 ( 48058.2) =     11.6%
  Interference by Ca SKB`     IV    at  12.4050 ( 48229.5) =      5.2%
  Interference by Ca SKBN     IV    at  12.5300 ( 48716.1) =     31.7%
  Interference by Cs LB2      V     at  12.5610 ( 48836.8) =    267.7%
  Interference by Ti KB3      V     at  12.5720 ( 48879.6) =     79.1%
  Interference by Ti KB1      V     at  12.5720 ( 48879.6) =    140.3%

Note the significant interference from the 2nd order P Ka tails.  For the low off-peak side we obtain this:

Code: [Select]

For Na ka (lo-off),    TAP at  11.3676 angstroms( 44191.1), at an assumed concentration of 1 wt.%
  Interference by Cs LG3      V     at  11.1660 ( 43406.4) =       .3%
  Interference by K  SKA3``   III   at  11.1710 ( 43425.9) =       .1%
  Interference by K  SKA`     III   at  11.1850 ( 43480.4) =       .2%
  Interference by K  SKA``    III   at  11.2150 ( 43597.1) =       .8%
  Interference by K  KA1      III   at  11.2270 ( 43643.9) =    123.0%
  Interference by K  KA2      III   at  11.2370 ( 43682.8) =     89.0%
  Interference by Na SKB^4          at  11.3140 ( 43982.5) =       .5%
  Interference by Cs SLA9     IV    at  11.3830 ( 44251.1) =     31.0%
  Interference by P  SKB^4    II    at  11.3900 ( 44278.4) =     12.5%
  Interference by P  SKB``    II    at  11.4230 ( 44406.8) =      8.9%
  Interference by Cs SLA8     IV    at  11.4310 ( 44438.0) =     18.8%
  Interference by Cs SLA7     IV    at  11.4660 ( 44574.2) =      8.9%
  Interference by Cs SLA6     IV    at  11.5040 ( 44722.1) =      2.8%
  Interference by Cs SLA5     IV    at  11.5160 ( 44768.8) =      1.8%
  Interference by Cs SLA3     IV    at  11.5520 ( 44909.0) =       .4%
  Interference by Cs LA1      IV    at  11.5710 ( 44983.0) =     13.7%
  Interference by Cs LA2      IV    at  11.6090 ( 45130.9) =       .2%

On the low off-peak side we see significant interference from the 2nd order P Ka satellite lines.  This situation definitely calls for the multi-point off-peak background method!

[John Donovan]

Ok, so the negative Na result is an obvious problem.  But how do we know that the positive results from K and Cs are real?

On the K front, Brian presented the K wavescan, and since the K Ka and K Kb peaks are both present that is highly suggestive that trace K is present in the RbTiOPO4 material. Here is my wavescan (6 seconds per point), and even with that short a scan time, the K Ka peak is clearly visible (I didn't scan wide enough to catch the K Kb peak):



But could this be a secondary (or higher order) peak from one of the major elements?  Let's go back to PFE and this time use the Standard Assignments dialog to check for nominal on-peak interferences.



So there is a significant interference from Rb but it is 4th order so it should be very weak, and the interfering Rb peak positions are hundreds of spectrometer units away from the K on-peak position... and the presence of both the Ka and Kb peaks (in Brian's scan) is very consistent with potassium actually being present.  And his K Kb peak is smaller than his K Ka peak, again consistent with potassium being present.

But ideally we'd probably want to perform an interference correction for Rb on K using any Rb standard that we know doesn't contain potassium (!), to be sure. Or perform a blank measurement on a pure RbTiOPO4 standard.  Which is what we are trying to create here so round and round it goes!

[John Donovan]

On the Cs front, I'm going to agree with Brian again.

A close look at the Cs La on LPET wavescan shows a nasty tail from the Ti Ka on the Cs La peak position.



A measurement using a large LIF crystal (instead of the PET crystal I used) would be a much better measurement as the peak position goes from a very low spectrometer angle to a very high spectrometer angle.

This is a great example of why trace element interpretation can be problematic!   

I'm going to try again with multi-point bgds on Na and Cs on a LLIF crystal over the weekend.

[Brian Joy]

So there is a significant interference from Rb but it is 4th order so it should be very weak, and the interfering Rb peak positions are hundreds of spectrometer units away from the K on-peak position... and the presence of both the Ka and Kb peaks (in Brian's scan) is very consistent with potassium actually being present.  And his K Kb peak is smaller than his K Ka peak, again consistent with potassium being present.

But ideally we'd probably want to perform an interference correction for Rb on K using any Rb standard that we know doesn't contain potassium (!), to be sure. Or perform a blank measurement on a pure RbTiOPO4 standard.  Which is what we are trying to create here so round and round it goes!

Note that Rb K_edge = 15.199 keV.  I used beam energy = 15 keV.

[John Donovan]

So there is a significant interference from Rb but it is 4th order so it should be very weak, and the interfering Rb peak positions are hundreds of spectrometer units away from the K on-peak position... and the presence of both the Ka and Kb peaks (in Brian's scan) is very consistent with potassium actually being present.  And his K Kb peak is smaller than his K Ka peak, again consistent with potassium being present.

But ideally we'd probably want to perform an interference correction for Rb on K using any Rb standard that we know doesn't contain potassium (!), to be sure. Or perform a blank measurement on a pure RbTiOPO4 standard.  Which is what we are trying to create here so round and round it goes!

Note that Rb K_edge = 15.199 keV.  I used beam energy = 15 keV.

Excellent point!   This certainly explains why you didn't see that interference!  I should have the nominal interference calculation in PFE check for that!

Edit by John: I actually ran my trace elements at 20 keV (100 nA), so that is why PFE printed the Rb Ka interference out!

But still it would be a low overvoltage (~1.3), so unlikely to show up well as a 4th order interference.

I also will run my UC Berkeley RbTiOPO4 against the CalChemist material and see if there's any difference in the apparent K signal

[Probeman]

I ran a more careful characterization on both the CalChemist and the original UC Berkeley RbTiOPO4 material and thought I would share how I set up the analysis for the same trace elements as before, that is K, Cs, Na, Ca and Mg.

For starters I decided to measure using the same crystals, specifically the large PET (LPET) crystal for Cs la, which puts the spectrometer at a fairly low sin theta and due to the lower spectral resolution of the PET crystal compared with LIF or LLIF, to just deal with the over lap from the tail of the Ti ka line.  So I also measured Ti for this interference correction. 

Also I utilized multi-point bgds (MPB) on all the trace elements so we have more leeway in fitting the backgrounds in post processing.  Measuring traces in RbTiOPO4 isn't as bad a monazite, which is a REE "zoo", but it does have its interesting background issues.

So first let's start with K Ka. Here is a wavescan plot of the RbTiOPO4 (CalChemist) material using 12 secs per point with the original (traditional) off-peaks shown in magenta:



Now the same, but with the multi-point bgds I selected (four on each side):



Here is an example of one point analysis showing the MPBs selected automatically by the software, though they can be manually selected as well (I overlaid the wavescan from above to show the K Ka peak):



Note the exponential fit based on the 4 selected multi-point background measurements (320 sec on-peak, and 160 seconds on each of the 4 off-peaks).

[Probeman]

Now let's look at Cs La.

Here is the Cs wavescan (20 keV, 100 nA, 10 um 200 points):



Now the same plot zoomed in Y and showing the MPBs for Cs La. Note the exponential fit and the Ti ka tails:



Now if we plot up the MPBs with the wavescan data we can immediately see the background fit problem. And that is that there is *no background* between the Ti ka and Ti Kb peaks!



We can have the program only use 1 off-peak on the low side of the cs La peak to avoid the background between the Ti ka and Ti Kb peaks, but the single low side background is still probably on the tail of the Ti KLb peak... yes, yes, we should be measuring Cs La using an LIF crystal, but this is still instructive to see what we can do in adverse circumstances...

If we select only one background on the low side we get this, which is an improvement, but still not good enough:



I'm going to perform a wider scan this time going further on the low side to see if we ever get to actual background past the Ti Kb peak...

[Probeman]

Just for completeness, here are the plots for Na, Ca and Mg. First here is Na Ka. There could be an interference on Na Ka from the tail of the P Ka 3rd order peak as seen here:



And indeed if I analyze my YPO4 standard get about 600-700 PPM of Na apparently from an interference by P Ka 3rd order:

ELEM:        K      Cs      Na      Ca      Mg      Ti       P      Rb       O       Y   SUM 
   275    .000   -.007    .063    .000   -.003    .006  16.836    .000  34.805  48.350 100.050
   276    .001   -.015    .070   -.002   -.001    .004  16.868    .000  34.805  48.350 100.081
   277    .005   -.010    .068   -.002    .002    .004  16.842    .000  34.805  48.350 100.064

AVER:     .002   -.011    .067   -.001    .000    .005  16.849    .000  34.805  48.350 100.065
SDEV:     .002    .004    .004    .001    .002    .001    .017    .000    .000    .000    .016
SERR:     .001    .002    .002    .001    .001    .001    .010    .000    .000    .000
%RSD:   119.51  -39.50    5.75  -88.93 -523.22   22.07     .10     .00     .00     .00

There does indeed appear to be a small Ca peak..





But not much Mg.  The quant will tell us.

[Brian Joy]

We can have the program only use 1 off-peak on the low side of the cs La peak to avoid the background between the Ti ka and Ti Kb peaks, but the single low side background is still probably on the tail of the Ti KLb peak... yes, yes, we should be measuring Cs La using an LIF crystal, but this is still instructive to see what we can do in adverse circumstances...

If we select only one background on the low side we get this, which is an improvement, but still not good enough:



I'm going to perform a wider scan this time going further on the low side to see if we ever get to actual background past the Ti Kb peak...

But keep in mind that the Ti K absorption edge produces a discontinuity in the continuum on the low sine(theta) side of the Ti Kb peak.  Measurement of background on opposing sides of an absorption edge could cause the concentration of a trace element to be overestimated significantly (aside from problems with the high sine(theta) tail on Ti Ka).  Why not just choose "background" offsets (using a non-linear model) on either side of the Cs La peak position and all on the high-sine(theta) tail of Ti Ka, especially since the matrix is essentially constant in composition?

[Probeman]

But keep in mind that the Ti K absorption edge produces a discontinuity in the continuum on the low sine(theta) side of the Ti Kb peak.  Measurement of background on opposing sides of an absorption edge could cause the concentration of a trace element to be overestimated significantly (aside from problems with the high sine(theta) tail on Ti Ka).  Why not just choose "background" offsets (using a non-linear model) on either side of the Cs La peak position and all on the high-sine(theta) tail of Ti Ka, especially since the matrix is essentially constant in composition?

Absolutely.  That might work too.  Here's an example from my Amer. Min. paper (2011) of Al Ka in quartz where the tail of the Si Ka peak sits on the Al peak:



It will be interesting to see the shape of the continuum on the low side.  Unfortunately it will have to wait a few days as our x-axis has just failed on our SX100 stage.   

I'm excited to attempt an interference correction from the Ti overlap on Cs La on this PET crystal.  You know- "failure mode" testing...   

[Probeman]

Good news, my Sx100 stage is operational again and I acquired a nice multi-point background run this weekend on the RbTiOPO4 (both UC Berkeley and CalChemist material).

I'll post the quant results tomorrow... in the meantime here is the MPB background fit for the Cs La line in this matrix:



Brian Joy is absolutely correct: a sane person would run this element on an LiF crystal due to the nasty Ti ka interference, not to mention the absorption edge issue on the other side of the Ti Kb peak, but when the quantitative iterated interference correction is applied from the TiO2 standard, a very interesting thing happens (but only if the same MPB positions were utilized for both the standard and the unknown).  Tomorrow...

Strange when you think about it, that we often run our EPMA standards and unknowns differently, because every other analytical field I know of generally treats unknowns and controls as much the same as possible to rule out problems from things we don't know about.  Of course I understand the reason (to save time), but still.

[Probeman]

So we'll get back to the Cs La trace characterization in a moment because it is quite interesting, but in the meantime I ran a wider wavescan on the RbTiOPO4 to see the Cs La background on the low side of the Ti Kb peak and it appears to be measuring the actual background (whether the Ti K edge is complicating things or not remains to be seen, as I have an "ace up my sleeve" with the quantitative interference correction!).



In the meantime here are the results starting with potassium. First a plot of the multi-point-backgrounds (MPB) with a fairly high precision wavescan using 12 seconds per point:



The Ar absorption edge is obvious but there appears to be no other continuum artifacts to be concerned with as seen in this closer look:



Of most concern would be the possibility that the Rb 4th order reflections could be interfering with the K emission line and creating an apparent K concentration.  But I am not concerned for three reasons:

1. The Rb K edge is 15.2 keV and although we ran the acquisition at 20 keV, that is still a very low overvoltage (~1.31) so our sensitivity should be very poor.

2. Any 4th order reflections that are present should be dramatically suppressed by the use of differential mode in PHA.

3. The position of the 4th order reflections are off enough to suspect that they are not at the K Ka position, though sometimes, these calculations can be off a little. But the best evidence against the Rb Ka 4th order reflections being present is that we should be able to resolve the Ka1/Ka2 split and instead we see a single clean peak which makes sense for K ka.

Finally, we should expect some K to be present as this is a RbTiOPO4 material and potassium would be expected as a contaminant.

[Probeman]

Now for Na it is a little more messy.  We have some P K 2nd order reflections that could easily interfere with the Na backgrounds. The P Ka1/Ka2 2nd order reflection is obvious, while the small peak to the left could be the satellite P SKA6 2nd order and that seems to be confirmed by the larger P SKBX 2nd order reflection further to the left.



But all in all, the backgrounds selected by the MPB method (points circled in red), seem to be otherwise pretty good, though it is a nasty part of the spectrum.

[Probeman]

Now let's turn to Ca and Mg.  Both appear to be pretty clean with respect to backgrounds. First Ca Ka:



This scan was 20 seconds per point, so again fairly high precision. 

For Mg Ka, we can see a small Ti Ka satellite (4th order!) reflection, but otherwise the background appears free from artifacts (again 20 seconds per point):

[Probeman]

Now for the trace characterization of Cs La using a PET crystal in our RbTiOPO4 matrix.

As Brian Joy has pointed out, we really should be using an LIF crystal for this analysis, due to the higher resolution and higher sin theta of the LIF for Cs La, but let's run the experiment. Recall the significant interference from Ti ka due to the tail of the Ti Ka peak:



If we calculate the nominal interferences using the Standard Assignments dialog, we obtain this prediction assuming Gaussian peak overlaps:



So, without an interference specified let's see what we obtain for our trace elements. First a report on the analytical setup:

Un    4 CalChemist RbTiOPO4 #2
TakeOff = 40.0  KiloVolt = 20.0  Beam Current = 100.  Beam Size =   10
(Magnification (analytical) =  20000),        Beam Mode = Analog  Spot
(Magnification (default) =     1000, Magnification (imaging) =   1000)
Image Shift (X,Y):                                         .00,    .00

Compositional analyses were acquired on an electron microprobe (Cameca SX100 (TCP/IP Socket)) equipped with 5 tunable wavelength dispersive spectrometers. Operating conditions were 40 degrees takeoff angle, and a beam energy of 20 keV. The beam current was 100 nA, and the beam diameter was 10 microns.

Elements were acquired using analyzing crystals LPET for K ka, Cs la, Ti ka, P ka, PET for Ca ka, LPET for K ka, Cs la, Ti ka, P ka, and TAP for Na ka, Mg ka.

The standards were TiO2 synthetic for Ti ka, Nepheline (partial anal.) for Na ka, Diopside (Chesterman) for Mg ka, Ca ka, Orthoclase MAD-10 for K ka, YPO4 (USNM 168499) for P ka, and Pollucite, PA-031 for Cs la.

The counting time was 80 seconds for Ti ka, P ka, 320 seconds for K ka, Cs la, and 400 seconds for Mg ka, Na ka, Ca ka. The off peak counting time was 80 seconds for Ti ka, P ka, 320 seconds for K ka, Cs la, and 400 seconds for Mg ka, Na ka, Ca ka. Off Peak correction method was Exponential for Ti ka, P ka, and Multi-Point for Na ka, Ca ka, Mg ka, K ka, Cs la.

Unknown and standard intensities were corrected for deadtime. Standard intensities were corrected for standard drift over time.

Results are the average of 12 points and detection limits ranged from .001 weight percent for K ka to .002 weight percent for Na ka to .003 weight percent for P ka.

Analytical sensitivity (at the 99% confidence level) ranged from .044 percent relative for Ti ka to 4.937 percent relative for Cs la to 70.071 percent relative for Na ka.

The exponential or polynomial background fit was utilized.

See John J. Donovan, Heather A. Lowers and Brian G. Rusk, Improved electron probe microanalysis of trace elements in quartz, American Mineralogist, 96, 274­282, 2011


And here are the results (without the interference correction for Ti on Cs La):

Un    4 CalChemist RbTiOPO4 #2, Results in Elemental Weight Percents
 
ELEM:        K      Cs      Na      Ca      Mg      Ti       P      Rb       O
TYPE:     ANAL    ANAL    ANAL    ANAL    ANAL    ANAL    ANAL    SPEC    SPEC
BGDS:     MULT    MULT    MULT    MULT    MULT     EXP     EXP
TIME:   320.00  320.00  400.00  400.00  400.00   80.00   80.00     ---     ---
BEAM:    99.63   99.63   99.63   99.63   99.63   99.63   99.63     ---     ---

ELEM:        K      Cs      Na      Ca      Mg      Ti       P      Rb       O   SUM 
    37    .018    .028    .001    .003    .000  19.427  12.506  34.979  32.741  99.702
    38    .017    .028    .000    .003    .000  19.454  12.522  34.979  32.741  99.744
    39    .017    .028    .000    .001   -.001  19.485  12.505  34.979  32.741  99.756
    40    .018    .029    .001    .003    .000  19.516  12.542  34.979  32.741  99.828
    41    .019    .027    .002    .004    .001  19.465  12.500  34.979  32.741  99.736
    42    .018    .028   -.002    .002   -.001  19.446  12.511  34.979  32.741  99.723
    43    .018    .027    .001    .002   -.001  19.471  12.568  34.979  32.741  99.805
    44    .018    .026    .002    .002    .000  19.445  12.496  34.979  32.741  99.707
    45    .018    .026   -.002    .002    .000  19.488  12.478  34.979  32.741  99.730
    46    .018    .024    .001    .003    .000  19.527  12.567  34.979  32.741  99.860
    47    .018    .026   -.001    .003   -.001  19.489  12.544  34.979  32.741  99.797
    48    .019    .028    .001    .002   -.001  19.507  12.506  34.979  32.741  99.781

AVER:     .018    .027    .000    .002    .000  19.477  12.520  34.979  32.741  99.764
SDEV:     .000    .002    .001    .001    .001    .031    .029    .000    .000    .050
SERR:     .000    .000    .000    .000    .000    .009    .008    .000    .000
%RSD:     2.29    5.61  712.86   31.93 -247.65     .16     .23     .00     .00
STDS:      374    1125     336     358     358      22    1016     ---     ---


The Ti interference is around 270 PPM in the RbTiOPO4 matrix.  Now let's check our TiO2 standard which will be used for the interference correction:

St   22 Set   2 TiO2 synthetic, Results in Elemental Weight Percents
 
ELEM:        K      Cs      Na      Ca      Mg      Ti       P      Rb       O
TYPE:     ANAL    ANAL    ANAL    ANAL    ANAL    ANAL    ANAL    SPEC    SPEC
BGDS:     MULT    MULT    MULT    MULT    MULT     EXP     EXP
TIME:    40.00   40.00   40.00   40.00   40.00   40.00   40.00     ---     ---
BEAM:    99.85   99.85   99.85   99.85   99.85   99.85   99.85     ---     ---

ELEM:        K      Cs      Na      Ca      Mg      Ti       P      Rb       O   SUM 
   279    .001    .081    .001   -.003   -.001  59.882    .001    .000  40.050 100.011
   280    .003    .076    .002    .002    .003  59.955    .000    .000  40.050 100.090
   281    .002    .080    .003    .000    .000  59.991    .001    .000  40.050 100.126
   282    .002    .079   -.002    .003    .002  59.906   -.002    .000  40.050 100.039

AVER:     .002    .079    .001    .000    .001  59.934    .000    .000  40.050 100.067
SDEV:     .001    .002    .002    .003    .002    .049    .001    .000    .000    .052


Note the we see an apparent Cs concentration of 790 PPM in our TiO2 due to the interference from Ti Ka. 

Now we apply the interference correction by simply selecting Ti as the interfering element and TiO2 as the interference standard (because it contains no Cs, and contains a known amount of the interfering element Ti, and no other interfering elements). 

Remember, because the interference correction in Probe for EPMA is iterated and quantitative, the differences in the matrix corrections between the unknown (RbTiOPO4), and the interference standard (TiO2) are properly and automatically dealt with.

Un    4 CalChemist RbTiOPO4 #2, Results in Elemental Weight Percents
 
ELEM:        K      Cs      Na      Ca      Mg      Ti       P      Rb       O
TYPE:     ANAL    ANAL    ANAL    ANAL    ANAL    ANAL    ANAL    SPEC    SPEC
BGDS:     MULT    MULT    MULT    MULT    MULT     EXP     EXP
TIME:   320.00  320.00  400.00  400.00  400.00   80.00   80.00     ---     ---
BEAM:    99.63   99.63   99.63   99.63   99.63   99.63   99.63     ---     ---

ELEM:        K      Cs      Na      Ca      Mg      Ti       P      Rb       O   SUM 
    37    .018    .002    .001    .003    .000  19.428  12.506  34.979  32.741  99.677
    38    .017    .002    .000    .003    .000  19.454  12.521  34.979  32.741  99.719
    39    .017    .003    .000    .001   -.001  19.486  12.505  34.979  32.741  99.731
    40    .018    .003    .001    .003    .000  19.517  12.542  34.979  32.741  99.803
    41    .019    .001    .002    .004    .001  19.466  12.499  34.979  32.741  99.711
    42    .018    .002   -.002    .002   -.001  19.447  12.511  34.979  32.741  99.698
    43    .018    .001    .001    .002   -.001  19.472  12.568  34.979  32.741  99.780
    44    .018    .000    .002    .002    .000  19.445  12.496  34.979  32.741  99.682
    45    .018    .000   -.002    .002    .000  19.489  12.478  34.979  32.741  99.704
    46    .018   -.002    .001    .003    .000  19.528  12.567  34.979  32.741  99.835
    47    .018    .001   -.001    .003   -.001  19.489  12.543  34.979  32.741  99.772
    48    .019    .002    .001    .002   -.001  19.507  12.506  34.979  32.741  99.756

AVER:     .018    .001    .000    .002    .000  19.477  12.520  34.979  32.741  99.739
SDEV:     .000    .002    .001    .001    .001    .031    .029    .000    .000    .050
SERR:     .000    .000    .000    .000    .000    .009    .008    .000    .000
%RSD:     2.29  128.51  712.86   31.93 -247.65     .16     .23     .00     .00
STDS:      374    1125     336     358     358      22    1016     ---     ---

STKF:    .1102   .2652   .0583   .1676   .0644   .5616   .1496     ---     ---
STCT:   9129.3 11088.8  1550.4  7022.5  3286.5 64371.5  4913.6     ---     ---

UNKF:    .0002   .0000   .0000   .0000   .0000   .1753   .0763     ---     ---
UNCT:     12.9      .4      .0      .9     -.1 20095.1  2504.8     ---     ---
UNBG:     45.8   156.1    11.1    40.4    22.7   132.4     7.6     ---     ---

ZCOR:   1.1552  1.1604  2.6811  1.0545  1.8314  1.1110  1.6413     ---     ---
KRAW:    .0014   .0000   .0000   .0001   .0000   .3122   .5098     ---     ---
PKBG:     1.28    1.00    1.00    1.02    1.00  152.73  330.98     ---     ---
INT%:     ----  -95.91    ----    ----    ----    ----    ----     ---     ---


Note that with the interference correction turned on, the apparent 270 PPM of Cs now disappears, and the interference correction magnitude is -95.91 %, which tells us that all the apparent Cs was in fact spurious.

So now we see only around ~180 PPM of potassium and maybe 20-30 PPM of Ca, and that is all.