Author Topic: Standard/ unknown different coating?  (Read 5378 times)

UofO EPMA Lab

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Re: Standard/ unknown different coating?
« Reply #15 on: August 14, 2019, 12:46:14 pm »
While at M&M last week I was asked a question about analyzing standards in Probe for EPMA. That is one acquires data on a standard and then from the Analyze! window one clicks the Analyze button to get a quantitative analysis of that standard *as though it were an unknown*.

Of course if the standard is the primary (assigned) standard for that element, the element in question will iterate to the correct concentration, because the standard is analyzing itself as the standard. That is why the %VAR (percent variance) value for that element is displayed in parentheses- because it isn't really a test of the analytical quality. 

Of course it should be pointed out that even though Probe for EPMA only utilizes the intensities of the elements actually assigned as the primary standard for that element, if one is analyzing a standard sample as an unknown in the Analyze! window, the matrix corrections will not be able to exactly converge correctly on the (ideal or published) concentration of the assigned element for this primary standard, if there is something significantly wrong with the other (unassigned) elements in that standard sample.

So in the case of our Fe (pure metal) standard shown in the previous post, because we have analyzed carbon on a carbon coated standard, of course we detect a significant amount (~10 wt%) of carbon as being in the Fe metal standard. Now the matrix iteration correctly calculates the std k-factor for our pure metal standard (the one we are analyzing as an unknown!) as being 1.0, but when it calculates the matrix correction physics for our Fe standard as containing ~10 wt% carbon, of course it cannot converge to the 100% Fe as one might expect:

St  526 Set   3 Iron metal, Results in Elemental Weight Percents
 
ELEM:        N       C      Mo      Si      Ni       V      Cu       O      Fe      Cr      Mn
BGDS:      EXP     EXP     LIN     EXP     LIN     LIN     EXP     EXP     LIN     LIN     LIN
TIME:    40.00   40.00   40.00   40.00   20.00   20.00   20.00   40.00   20.00   20.00   20.00
BEAM:    49.56   49.56   49.56   49.56   49.56   49.56   49.56   49.56   49.56   49.56   49.56

ELEM:        N       C      Mo      Si      Ni       V      Cu       O      Fe      Cr      Mn   SUM 
   156   -.160  10.904   -.002    .011   -.006    .002   -.016    .357 102.982    .011    .008 114.091
   157   -.085  10.732   -.020    .007   -.019   -.013   -.003    .372 101.793   -.003   -.007 112.755
   158   -.285  10.792   -.025    .006    .011   -.002    .033    .432 102.560   -.019   -.009 113.495

AVER:    -.177  10.809   -.016    .008   -.004   -.004    .005    .387 102.445   -.003   -.003 113.447
SDEV:     .101    .087    .012    .002    .015    .007    .025    .040    .603    .015    .009    .669
SERR:     .058    .050    .007    .001    .008    .004    .015    .023    .348    .009    .005
%RSD:   -57.10     .81  -78.83   30.67 -328.34 -169.36  544.36   10.29     .59 -433.32 -346.16

PUBL:     n.a.    n.a.    n.a.    n.a.    n.a.    n.a.    n.a.    n.a. 100.000    n.a.    n.a. 100.000
%VAR:      ---     ---     ---     ---     ---     ---     ---     ---  (2.45)     ---     ---
DIFF:      ---     ---     ---     ---     ---     ---     ---     ---  (2.45)     ---     ---
STDS:      604     506     542     514     528     523     529     913     526     524     525


And again, this doesn't matter for any other sample that uses this Fe standard, because only the measured Fe intensities (from the standard sample), and the (ideal) composition from the standard database is being utilized for the std k-factor calculation, but if one really wants to see the composition of any carbon coated standards analyzed as though they were actual unknowns, one can simply select all the standards (except of course the carbon standard!), then click the Elements/Cations button and then click the carbon row and check the "Disable Quant" checkbox and click OK and OK. Then we will get output like this when analyzing our carbon coated standards as unknowns:

St  526 Set   3 Iron metal, Results in Elemental Weight Percents
 
ELEM:        N       C      Mo      Si      Ni       V      Cu       O      Fe      Cr      Mn
BGDS:      EXP     EXP     LIN     EXP     LIN     LIN     EXP     EXP     LIN     LIN     LIN
TIME:    40.00     ---   40.00   40.00   20.00   20.00   20.00   40.00   20.00   20.00   20.00
BEAM:    49.56     ---   49.56   49.56   49.56   49.56   49.56   49.56   49.56   49.56   49.56

ELEM:        N     C-D      Mo      Si      Ni       V      Cu       O      Fe      Cr      Mn   SUM 
   156   -.124     ---   -.002    .011   -.006    .002   -.016    .299 100.558    .011    .008 100.741
   157   -.066     ---   -.020    .007   -.018   -.012   -.003    .311  99.405   -.003   -.007  99.595
   158   -.221     ---   -.025    .007    .011   -.002    .032    .362 100.161   -.018   -.009 100.297

AVER:    -.137     ---   -.016    .008   -.004   -.004    .005    .324 100.041   -.003   -.003 100.211
SDEV:     .078     ---    .012    .002    .014    .007    .025    .033    .586    .014    .009    .578
SERR:     .045     ---    .007    .001    .008    .004    .014    .019    .338    .008    .005
%RSD:   -57.14     ---  -78.83   30.68 -328.37 -169.35  544.25   10.33     .59 -433.25 -346.11

PUBL:     n.a.    n.a.    n.a.    n.a.    n.a.    n.a.    n.a.    n.a. 100.000    n.a.    n.a. 100.000
%VAR:      ---     ---     ---     ---     ---     ---     ---     ---   (.04)     ---     ---
DIFF:      ---     ---     ---     ---     ---     ---     ---     ---   (.04)     ---     ---
STDS:      604     ---     542     514     528     523     529     913     526     524     525
« Last Edit: August 14, 2019, 12:47:48 pm by UofO EPMA Lab »
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