Wavelength and energy-dispersive X-ray microanalysis with EMA and SEM-EDXRA on thin sections of soils.

Abstract

Organic matter, minerals and iron-manganese nodules were studied in thin sections of soils with an electron microprobe analyzer (EMA) and a combination of a scanning electron microscope (SEM) and an energy-dispersive X-ray analyzer (EDXRA). Both instruments were used to estimate the presence and nature of chemical elements in two selected areas, one containing a combination of organic and mineral material and another inside an iron-manganese nodule. The detection of organic matter proved problematic. Of the light elements, N could not be detected with EMA and O was detected but was not specific to organic matter. EMA could not be used for C because of the C coating of the thin section. SEM-EDXRA only detected heavier elements. EMA produced somewhat better X-ray images of heavier elements, especially from an iron-manganese nodule. However, with organic material, SEM-EDXRA X-ray images were similar to or slightly better than EMA. An advantage of SEM-EDXRA over EMA is that the soil material can be analysed at various magnifications with a much higher limit, and point analysis can be made of loose material. For soil material, SEM-EDXRA was better as a routine instrument which solved most problems. EMA can be used as a complementary instrument. Other microanalytical techniques such as the ion microprobe mass analyzer (IMMA) were necessary to analyse light elements in organic material of soils. (Abstract retrieved from CAB Abstracts by CABI’s permission)