This is a little weird, but I wanted to compare running trace elements in zircon on WDS and EDS, but wondered if using the L lines for Th, U and Hf might be better than the M series lines for EDS. Unfortunately our Thermo system does not return the background count rate since it utilizes a filter method for the background correction, so I cannot compare the detection limits and instead can only look at the variance in wt % units.
The conditions for simultaneous acquisition of the WDS and EDS spectra were:
KiloVolt = 20.0 Beam Current = 50.0 Beam Size = 10
and 640 sec on-peak with 640 sec off-peak counting times. Normally I would run WDS elements at 100 or 200 or more nA, but the SDD pulse processor cannot handle much more than that (EDS deadtime was ~30% at 50 nA).
The results on a synthetic zircon (Oak Ridge) using off-peak backgrounds is:
Formula ZrSiO4 is Calculated by Difference from 100%
Un 4 std 257 as unk, Results in Elemental Weight Percents (Off-peak background correction, no blank)
ELEM: Th Hf U P Y O Zr Si
TYPE: ANAL ANAL ANAL ANAL ANAL FORM FORM FORM
BGDS: LIN LIN LIN LIN LIN
TIME: 640.00 640.00 640.00 640.00 640.00 --- --- ---
BEAM: 50.39 50.39 50.39 50.39 50.39 --- --- ---
ELEM: Th Hf U P Y O Zr Si SUM
74 .002 .015 -.001 .027 .008 34.936 49.738 15.314 100.040
75 -.002 .015 .004 .028 .011 34.937 49.736 15.313 100.042
76 -.002 .016 .013 .025 .003 34.933 49.736 15.313 100.038
77 -.014 .018 .003 .025 .001 34.937 49.747 15.317 100.034
78 .009 .018 .014 .024 .008 34.928 49.727 15.311 100.040
79 .000 .021 .017 .024 .000 34.929 49.733 15.312 100.037
80 .013 .020 -.002 .025 .005 34.931 49.734 15.313 100.038
81 .005 .022 .003 .025 .006 34.932 49.733 15.312 100.039
82 .008 .019 .008 .025 .006 34.931 49.731 15.312 100.040
83 -.002 .017 .007 .025 .002 34.934 49.739 15.314 100.037
AVER: .002 .018 .007 .025 .005 34.933 49.736 15.313 100.038
SDEV: .008 .003 .006 .001 .003 .003 .006 .002 .002
SERR: .002 .001 .002 .000 .001 .001 .002 .001
%RSD: 431.39 13.98 94.71 4.86 69.39 .01 .01 .01
There is a very small interference from Si ka on Hf Ma:
Interference by Si KA1 at 7.12560 ( 27661.8) ( -1609.2)
Interference by Si KA2 at 7.12970 ( 27677.8) ( -1593.2)
and also a small interference from Zr La on P Ka:
Interference by Zr LA1 at 6.07170 ( 69386.5) ( -986.55)
Since I did not analyze for Si or Zr we cannot perform a proper interference correction, but we can assign the sample as a blank to itself. By assigning the sample as a blank to itself, everything is normalized to zero, but the number we want to look at is the variance in either case. After all elements are assigned as a blank correction (assuming a zero concentration for each) we can see the results here:
Formula ZrSiO4 is Calculated by Difference from 100%
Un 4 std 257 as unk, Results in Elemental Weight Percents (Off-peak background correction, with blank)
ELEM: Th Hf U P Y O Zr Si
TYPE: ANAL ANAL ANAL ANAL ANAL FORM FORM FORM
BGDS: LIN LIN LIN LIN LIN
TIME: 640.00 640.00 640.00 640.00 640.00 --- --- ---
BEAM: 50.39 50.39 50.39 50.39 50.39 --- --- ---
ELEM: Th Hf U P Y O Zr Si SUM
74 .000 -.003 -.007 .002 .003 34.918 49.767 15.323 100.002
75 -.004 -.003 -.002 .002 .006 34.918 49.765 15.322 100.003
76 -.004 -.002 .007 .000 -.002 34.914 49.765 15.322 100.000
77 -.016 .000 -.004 .000 -.004 34.918 49.776 15.326 99.996
78 .007 .000 .007 -.001 .004 34.910 49.755 15.319 100.001
79 -.002 .003 .010 -.002 -.005 34.911 49.761 15.321 99.998
80 .011 .001 -.008 -.001 .000 34.913 49.762 15.321 100.000
81 .003 .004 -.004 .000 .001 34.914 49.761 15.321 100.001
82 .006 .001 .002 .000 .001 34.912 49.759 15.320 100.001
83 -.004 -.001 .000 .000 -.003 34.915 49.768 15.323 99.998
AVER: .000 .000 .000 .000 .000 34.914 49.764 15.322 100.000
SDEV: .008 .003 .006 .001 .003 .003 .006 .002 .002
SERR: .002 .001 .002 .000 .001 .001 .002 .001
Note that the variance does not change from the application of a blank correction. Also just for fun I ran the same analyses using the MAN background correction and as expected the variances are smaller (and would have taken half the time since the off-peak measurements are not necessary!):
Formula ZrSiO4 is Calculated by Difference from 100%
Un 4 std 257 as unk, Results in Elemental Weight Percents (MAN background correction, with blank)
ELEM: Th Hf U P Y O Zr Si
TYPE: ANAL ANAL ANAL ANAL ANAL FORM FORM FORM
BGDS: MAN MAN MAN MAN MAN
TIME: 640.00 640.00 640.00 640.00 640.00 --- --- ---
BEAM: 50.39 50.39 50.39 50.39 50.39 --- --- ---
ELEM: Th Hf U P Y O Zr Si SUM
74 .004 .002 -.004 .001 -.001 34.915 49.762 15.321 100.002
75 .001 .001 .001 .003 .002 34.916 49.760 15.321 100.005
76 -.003 .002 .001 -.001 -.001 34.914 49.765 15.322 99.999
77 -.012 .000 .001 .000 .002 34.916 49.768 15.323 99.999
78 -.004 -.001 -.003 .000 .005 34.915 49.765 15.322 100.000
79 -.001 .000 .004 -.001 .001 34.913 49.762 15.321 99.999
80 .010 -.001 -.002 -.001 -.001 34.912 49.761 15.321 100.000
81 -.001 -.002 .000 .000 -.001 34.915 49.766 15.323 99.999
82 .004 .000 -.002 .000 -.005 34.914 49.765 15.322 99.999
83 -.004 -.002 -.002 -.001 -.003 34.915 49.769 15.324 99.997
AVER: -.001 .000 .000 .000 .000 34.915 49.764 15.322 100.000
SDEV: .006 .001 .002 .001 .003 .001 .003 .001 .002
SERR: .002 .000 .001 .000 .001 .000 .001 .000
But what about EDS analyses? Next let's compare using the L and M series lines for Th, U and Hf by EDS...