Stoichiometry to Another Element

EPMA Probe

Stoichiometry to Another Element

Yet another option for recalculation is the element relative to another element (by stoichiometry). This calculation is similar to the "element by stoichiometry to oxygen" as described below, however the user may select any other analyzed (acquired) or specified element as the stoichiometric basis element.

 

This calculation can be used in combination with the other calculations to handle unusual analytical situations. For example, in the following analysis of an silica sample, the results revealed significant contamination of the material with Fe and Ca. Investigation using other techniques, implied that the Fe was in the form of Fe2O3 (hematite), and the Ca was present as CaCO3 (calcium carbonate). Aside from the effect of inhomogeneity on the matrix correction, it was desirable to improve the calculation by calculating Si by difference and C by stoichiometry to Ca as follows :

 

 

 Analysis of sample  un   2   seoj #3 random                         

 Total Number of Data Points =   6            Number of "G" Data Points =   3

 Average Beam Counts =   79092.                  Average Base Time =    10.00

 Average Sample Z-bar =   11.480            Average ZAF Iterations =    2.333

 Oxygen Calculated by Cation Stoichiometry and Included in  Matrix Correction

 Element : Si  is Calculated by Difference from a Sum of 100.0 Weight Percent

 Element : C   is Calculated Relative to Element Ca   at    1.000 to 1.0 Atom

 

 Results in Weight Percent :

 

        O       Si      C       La      F       SUB  

 

 SPEC  51.526  39.743   1.134    .000    .000  92.403

 SDEV   2.932  11.897   1.939    .000    .000

 

 BGD:   MAN     MAN     MAN     MAN     MAN     MAN

 

        Fe      Al      Ca      Mg      Mn      S       SUM  

  133    .054    .018    .012    .009    .000    .000 100.000

  134  10.696    .467  11.253    .010    .054    .000 100.000

  135    .119    .013    .083    .004    .000    .000 100.000

 

 AVER   3.623    .166   3.782    .008    .018    .000 100.000

 SDEV   6.126    .261   6.470    .003    .031    .000

 SERR   3.537    .151   3.735    .002    .018    .000

 

 KRAT   .0306   .0013   .0353   .0001   .0001   .0000

 ZCOR  1.1992  1.2245  1.0981  1.3804   .9338   .8713

 KRAW   .0451   .0029   .2072   .0001   .0002   .0000

 P/B:   14.07    4.78   43.69    1.45    1.07     .92

 

 

 Results in Elemental Mole Percents :

 

        O       Si      C       La      F    

 

 AVER  65.743  28.728   2.004    .000    .000

 SDEV   1.571   7.841   3.430    .000    .000

 

        Fe      Al      Ca      Mg      Mn      S       SUM  

  133    .019    .014    .006    .007    .000    .000 100.000

  134   4.069    .368   5.965    .009    .021    .000 100.000

  135    .043    .010    .041    .003    .000    .000 100.000

 

 AVER   1.377    .130   2.004    .006    .007    .000 100.000

 SDEV   2.332    .206   3.430    .003    .012    .000

 

 

 Results in Oxide Weight Percents using Custom Cation Oxide Ratios :

 

        O       SiO2    CO2     La2O3   F    

 

 AVER    .000  85.024   4.153    .000    .000

 SDEV    .000  25.452   7.104    .000    .000

 

        Fe2O3   Al2O3   CaO     MgO     MnO     SO3     SUM  

  133    .077    .035    .017    .014    .000    .000 100.000

  134  15.293    .883  15.745    .017    .070    .000 100.000

  135    .170    .024    .116    .006    .000    .000 100.000

 

 AVER   5.180    .314   5.292    .013    .023    .000 100.000

 

 

Note that Fe was recalculated as Fe2O3 and C was added relative to Ca by stoichiometry. This calculation can be applied in numerous other ways to a variety of analytical situations. Consider the example below. Here, the user decides to calculate CO2 on the basis of moles of CaO, rather than by stoichiometry to oxygen.

 

 Analysis of sample  st 141   set  1   dolomite (Harvard #105064)             

 Total Number of Data Points =   3            Number of "G" Data Points =   3

 Average Beam Counts =    9102.                  Average Base Time =    10.00

 Average Sample Z-bar =   10.875            Average BNA Iterations =    5.000

 CO2   is Calculated Relative to Oxide CaO    at    2.000 to 1.0 Mole

 

 Results in Weight Percent :

 

        CO2     SUB  

 

 SPEC  47.791  47.791

 SDEV    .071

 

 BGD:   MAN     MAN

 

        CaO     MgO     SUM  

    9  30.501  21.735 100.109

   10  30.424  21.769  99.947

   11  30.420  22.135 100.301

 

 AVER  30.448  21.880 100.119

 SDEV    .046    .222

 SERR    .026    .128

 

 PUBL  30.560  21.880 100.186

 %VAR   -.365   -.001

                   *

 

 UNBE  1.0496  1.2242

 KRAW   .5338  1.0000

 P/B:     .00     .00

 

 

 Results in Oxide Mole Percents :

 

        CO2  

 

 AVER  50.002

 SDEV    .139

 

        CaO     MgO     SUM  

    9  25.053  24.841 100.000

   10  25.028  24.917 100.000

   11  24.922  25.233 100.000

 

 AVER  25.001  24.997 100.000

 SDEV    .069    .208