Preparation of polished surfaces may involve the use of an oil (either to suspend/disperse the polishing media, or to lubricate the process). Such oil is often not fully removed by rinsing or ultra-sonicating with alcohol. This can lead to problems during electron-probe microanalysis.
In advance of carbon-coating a sample in preparation for such analysis, Long (1977) recommended cleaning the sample with the use of petroleum ether in conjunction with an ultrasonic bath, as quoted below:
“It is perhaps worth noting here that the cleanliness of the specimen surface is of considerable importance in achieving an effective coating: careful degreasing in Analytical Reagent-grade petroleum ether in an ultrasonic cleaning bath, followed by washing in ethanol, is recommended.”
Excerpted from: Section III. Specimen Preparation, B. Surface Coating (page 299) of:
Long, J.V.P., 1977. Electron probe microanalysis. Chapter 6 in Physical Methods in Determinative Mineralogy, second edition, J. Zussman, ed., Academic Press, New York, pp. 273-341.
Petroleum ether (CAS Registry Number 8032-32-4, boiling point 35-60 Celsius) has several synonyms or near synonyms: ligroin, ligroine, naphtha solvent, naphtha petroleum, petroleum spirit, petroleum benzin, rubber solvent, etc. General details can be found at:
https://en.wikipedia.org/wiki/Petroleum_ether http://www.cdc.gov/niosh/docs/1970/77-192.htmlPetroleum ether is an effective degreasing agent. Unlike ethanol, it does not dissolve “permanent marker”. Also, unlike acetone, it does not appear to have any effect (in the short term) on the epoxies commonly used for mounting samples for electron-probe microanalysis. Petroleum ether is insoluble in water, but is both highly volatile and highly flammable. It should be kept away from any rubber (O-rings etc.). It is probably preferable to undertake handling of small volumes of petroleum ether in an appropriate fume hood.
As petroleum ether is highly volatile, and can have negative health effects, the following procedure has been adopted in our laboratory:
1) Up to 3 thin sections or up to 5 one-inch diameter round mounts are placed (polished face up) in a transparent hard-plastic hinged box.
2) Sufficient petroleum ether is added to cover the samples (usually 10 to 15 mL).
3) The closed box is placed in a small water-filled ultrasonic bath, floating on the water.
4) The ultrasonic bath is covered by a hard plastic hood attached to an open vacuum line.
5) The ultrasonic bath is run for about 60 seconds.
6) The box is removed from the ultrasonic bath, and the samples withdrawn with the use of tongs. The samples are allowed to dry in air, and can now be rinsed with ethanol.
7) The remaining petroleum ether is decanted as chemical waste.
This text, and a photograph of our setup is given in the attached PDF.