BS ISO 22309:2011 - Page 2

Microbeam analysis. Quantitative analysis using energy-dispersive spectrometry (EDS) for elements with an atomic number of 11 (Na) or above. | Status: Confirmed, Current

1 Scope This International Standard gives guidance on the quantitative analysis at specific points or areas of a specimen using energy-dispersive spectrometry (EDS) fitted to a scanning electron microscope (SEM) or an electron probe microanalyser (EPMA); any expression of amount, i.e. in terms of percent (mass fraction), as large/small or major/minor amounts is deemed to be quantitative. The correct identification of all elements present in the specimen is a necessary part of quantitative analysis and is therefore considered in this International Standard. This International Standard provides guidance on the various approaches and is applicable to routine quantitative analysis of mass fractions down to 1 %, utilizing either reference materials or “standardless” procedures. It can be used with confidence for elements with atomic number Z < 10. Guidance on the analysis of light elements with Z < 11 is also given.

NOTE With care, mass fractions as low as 0,1 % are measurable when there is no peak overlap and the relevant characteristic line is strongly excited. This International Standard applies principally to quantitative analyses on a flat polished specimen surface. The basic procedures are also applicable to the analysis of specimens that do not have a polished surface but additional uncertainty components will be introduced.

There is no accepted method for accurate quantitative EDS analysis of light elements. However, several EDS methods do exist. These are the following:

1. a) Measuring peak areas and comparing intensities in the same way as for heavier elements. For the reasons explained in Annex D, the uncertainty and inaccuracy associated with the results for light elements will be greater than for the heavier elements.
2. b) Where the light element is known to be combined stoichiometrically with heavier elements (Z < 10) in the specimen, its concentration can be determined by summing the appropriate proportions of concentrations of the other elements. This is often used for the analysis of oxygen in silicate mineral specimens.
3. c) Calculation of concentration by difference where the light element percentage is 100 % minus the percentage sum of the analysed elements. This method is only possible with good beam-current stability and a separate measurement of at least one reference specimen and it requires very accurate analysis of the other elements in the specimen.

Annex D summarizes the problems of light element analysis, additional to those that exist for quantitative analysis of the heavier elements. If both EDS and wavelength spectrometry (WDS) are available, then WDS can be used to overcome the problems of peak overlap that occur with EDS at low energies. However, many of the other issues are common to both techniques.