SREL Reprint #2413

Thin-foil SEM analysis of soil and groundwater colloids: reducing instrument and operator bias

John C. Seaman

Advanced Analytical Center for Environmental Sciences, The University of Georgia,
Savannah River Ecology Laboratory, Drawer E, Aiken, South Carolina 29802

Abstract: Scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectrometry (EDS) has been widely used to characterize environmental colloids with little regard for instrumental limitations. Details associated with electron emission source, excitation voltage, and even sample-coating procedures are often omitted from publications because SEM techniques are generally considered routine. In the current study, the common analytical technique of depositing colloidal samples on polycarbonate filters (i.e., conventional analysis) and carbon coating for microanalysis was compared to a thin-foil mounting technique that enhances particle recognition and reduces the nonspecific background (i.e., Bremsstrahlung X-rays) that interferes with compositional analysis of submicron particles. Carbon-coated particle resolution was degraded compared to metal-coated samples, making it difficult to identify smaller particles or discern fine-grained aggregates during EDS analysis. The signal-to-noise ratio for the resulting EDS patterns was highly related to particle size, with smaller particles generating patterns dominated by Bremsstrahlung X-rays. For the thin-foil method, EDS patterns for smaller particles produced better signal-to-noise ratios that were independent of particle size. The ability to easily discriminate particles from the background and collect detailed EDS spectra with minimal analysis time makes this technique ideal for instrumental automation.

SREL Reprint #2413

Seaman, J.C. 2000. Thin-foil SEM analysis of soil and groundwater colloids: reducing instrument and operator bias. Environmental Science and Technology 34:187-191.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).