5.2. Calibration Curves
Calibration curves may be constructed which relate counts and concentration (Figures 5.2a and 5.2b). However, these require a large number of well-characterized standards with compositions bracketing the unknowns. The data used to make the curves must be taken at identical operating conditions (take-off angle, accelerating voltage and beam current) for all analyses.
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Figure 5.2a. Calibration curves for electron microprobe analysis of carbon in nickel steels (after Goldstein et al. 1981). |
Calibration curves must be constructed for each mineral group, but, because unknowns approximate the standards in compositions, corrections are unnecessary. The requirement of a great number of standards is especially difficult to satisfy especially with the accuracy required. In addition, this technique does not allow confident analysis of a truly unknown material.
| Figure 5.2b. Calibration curve of counts per second vs. weight percent MgO for chemically analyzed biotite, chlorite, staurolite, chloritoid, and garnet. The scatter in the data results from absorption (or fluorescence) due to compositional variations in the sample of oxides other than MgO. (after Bence and Albee 1968). |
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