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Electron Probe Microanalysis

The Electron Probe MicroAnalyser (EPMA) is a non-destructive technique for the analysis of polished solid materials.  The Department has a Cameca SX100 microprobe equipped with 5 wavelength dispersive spectrometers (WDS), capable of automated quantitative analysis and elemental mapping of all elements from B to U.   The instrument provides a service to the Earth Sciences Community as well as to all other departments within the University of Cambridge.  We also welcome work from outside the University, both academic and/or commercial. 

The EPMA is capable of quantitative analysis of individual points (1-30 microns in diameter) or over small (usually no more than 1mm2) areas of the sample surface to produce a quantitative (or qualitative) map.  An accuracy of about ±1% for major elements, and detection limits ranging from 20 to 1000 ppm can be attained. The nominal spatial resolution is approximately 2 µm.

1. Academic Staff Member:  Dr Marie Edmonds

2. Contact: Please email the lab manager,  Dr Iris Buisman (office M9)

First-time users should arrange to meet and discuss the measurement strategy appropriate to their research and techniques of sample preparation.

Peak demand for the EPMA typically occurs from October to January. At other times of the year, the EPMA is usually over-subscribed and waiting times are typically 3-6 weeks.  Please do contact Iris if you have an urgent requirement. To look at availability, please look at the online calendarPLEASE NOTE: The calendar is only meant to allow you see the availability.  To book a slot, please email .

3. Location:   East Wing - Ground floor Room N029 

4. Quick overview of technique:

4.1 Sample preparation of different techniques

Accurate analysis is possible only if the sample is well polished.  We have holders that can accommodate thin sections 46-48mm long x 10-30 mm width and stubs of 25 or 30mm diameter.

Samples that are not electrically conducting (including most rocks and minerals) must be coated with a conducting layer, typically carbon.  Please make sure your samples are coated before your session on the instrument.  Finding specific features for analysis in the electron probe can be difficult and time-consuming: users are therefore strongly encouraged to equip themselves in advance with 'maps' and/or photomicrographs (note that photomicrographs should preferably be reversed in printing, to match the probe microscope image).

4.2 Operation of the Electron Probe

Having mounted the specimens in the holder, this is loaded into the instrument via an airlock; after the vacuum has recovered (in a few minutes), the beam can be turned on. The instrument has a built-in optical microscope with zoom capability between approximately x100 and x1000, with polariser and analyser, and transmitted or reflected light. Scanning electron images can also be obtained but you are recommended to use the SEM to get high-quality images for publication.

Point analyses can be carried out one at a time, however, this involves waiting for each analysis to be completed, which typically takes ~3-6 minutes. A more efficient approach is to store all the points required and leave the instrument to run them automatically (usually overnight). This is particularly appropriate for recording lines or grids with large numbers of points. However, it is not suitable for analysing very fine scale features, where positioning of the beam is critical, since positional reproducibility on long automated runs cannot be guaranteed to better than a few microns.

4.3  Treatment of Results

The results can be exported as weight percent, oxide weight percent, atomic percent, etc. into ASCII files.  These files typically are <150kb.  Note: for oxides a valency is assumed for each element. In the case of Fe a value of 2 is used by default and it is up to the user to carry out any recalculation required to allow for some or all of the Fe being in the trivalent state. A total oxide wt.% between 99% and 101% is acceptable, variation within this range being attributable to counting statistics. A total which is significantly low may be caused by surface topography; alternatively it may indicate one or more missing elements, or the presence of water (note that water content estimated from the deficit in the total is only approximate).

In reporting results, concentrations below the level of statistical significance should be given as zero (not detected). For major-element analyses it is undesirable to express percentages with more than 2 digits after the decimal point. More digits are required, however, for lower concentrations as obtainable by WD analysis.

4.4  Precautions

Users are trained and supervised by the Electron Probe Technician. Operating instructions for the equipment are clearly set out. Provided these instructions are followed, no special hazards exist. The probe may only be operated out of normal working hours by users who have received permission and completed the "Out of Hours Permission Form" for this equipment.

Any instrumental fault should be reported to Iris Buisman. The room is air conditioned, doors must be kept shut. 

Under no circumstances should users attempt to rectify faults on the SX100 or associated computers. No files or programmes may be loaded onto the computer.

Full safety procedures for Cambridge users.

5.  References

New probe users are encouraged to read the following book in order to gain a somewhat deeper understanding of the technique:

  • Electron Microprobe Analysis and Scanning Electron Microscopy in Geology' by S.J.B. Reed, Cambridge Univ. Press, 2nd ed. 2005 (Dept. Library no. B.23.164.1).

Other useful links: