| Quantitative analysis and X-ray maps are produced for an initial qualitative analysis. If the qualitative analysis is incorrect, both the quantitative analysis and X-ray maps will be incorrect or incomplete. EDS manufacturers have toiled many years in perfecting their peak identification routines. Thermo prides itself on having the best peak identification routines of any EDS manufacturer.
But how can you as an operator confirm the quality of the automatic peak identification routine? Or, how can you manually identify an unlabelled peak with the highest confidence? The NORAN System 7 analysis software provides SpectraCheck to assist the user in obtaining the best qualitative results.
Background
The user interface of SpectraCheck appears to be nothing more than a simple EDS spectrum simulator. But SpectraCheck is much more: it is part qualitative analysis, part quantitative analysis, part spectrum background calculation, part statistical analysis. The algorithm takes the spectrum, performs a qualitative analysis, performs a quantitative analysis, calculates a spectrum background specifically for your detector and sample, creates a synthetic spectrum, then calculates the SpectraCheck X2 value. The complexities of the algorithm are transparent to you because it is the results that interests you.
How it works
Original EDS spectrum collected from the sample is loaded and an automatic qualitative analysis has been performed. SpectraCheck is enabled, and a synthetic spectrum is overlaid on the original data. The SpectraCheck value is a reasonable 12, but could be better.
Initial EDS Spectrum
An expanded view of the Mo peak with both synthetic and residual spectra overlaid shows that all peaks have not be accounted for in the analysis. Placing the spectra cursor on the residual peak of interest in the spectrum highlights all possible elements in the periodic table that have an energy peak in the near vicinity of the cursor. Selecting these elements one-by-one and minimizing the SpectraCheck value and the residual spectrum is the next task.
Expanded view of molybdenum peak with both synthetic and residual spectra overlaid
The first possible element selected is phosphorus. It has little effect on the synthetic and residual spectra or on the SpectraCheck value. This indicates that it is not the correct element.
Selecting phosphorus has little effect, indicating it is not the correct element
The next element to add is zirconium. It too has very little effect on either spectrum or the SpectraCheck value. Another element needs to be investigated.
Adding zirconium also has little effect, another element needs investigation
Selecting niobium has a profound effect on all parameters. The synthetic spectrum is a perfect match to the original data, the residual spectrum is flat, and the SpectraCheck value dropped significantly to 2.7. This indicates that the correct element has been selected for this peak identification.
Niobium has a profound effect on all parameters
By simple statistical and graphical means, it was found that both Nb and Mo are present in this peak. We are supremely confident that any subsequent analyses based on this qualitative analysis will be the best possible.
Conclusion
SpectraCheck is an easy method to verify automatic qualitative analysis or manual peak identification of EDS spectra. There is both a numerical statistical check and numerous graphical checks.
Using this advanced feature of the NORAN System 7 system gives users great confidence that their data interpretation is correct. |
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