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Goals for analytical accuracy:

Evaluate all aspects of calibration and analysis to obtain a more complete understanding of the sources of error in trace element EPMA. Develop entirely new methods for background acquisition and evaluation. Evaluate primary and secondary standards, and develop acquistion strategies that ensure both high precision and the most refined accuracy. For geochronology, secondary age standards are important, but EPMA is fundamentally a technique for assessing elemental concentration. Therefore, the veracity of the analysis must always rest on the accuracy of the estimated concentrations. Every effort must be made to ensure the highest accuracy.

The first step is recognizing that trace element EPMA critically depends on precise and accurate background analysis. As pk/bkg ratios approach unity, the background measurement becomes increasingly crucial (right) . Spectral analysis requires detailed evaluation of wavelength spectra at a level of precision commensurate with the peak acquisition.

True trace element secondary standards are difficult to come by, but if you can’t check against a known value, then try for a zero result in something appropriate that doesn’t have any of the trace element of interest (blank). “If you can’t analyze something, then see if you can analyze nothing…Because, if you can’t do nothing right, then you can’t do anything.”

Figures: Detailed step scan (upper right) of Pb M region of monazite (MOM) using PETH on a JEOL 8200 (UT-Austin). Substantial errors can result if background curvature and interferences both on peak and background are not appropriately addressed. Note that 2-pt linear interpolation will not yield an accurate background. Detailed WDS scanning is the first step. Error increases as net intensity (pk-bkg) decreases at lower concentration (lower right). For details, see Jercinovic et al. (2008).

 

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