Quantification by SEM–EDS in uncoated non-conducting samples

• SEM–EDS quantification of insulating samples without conductive coating is proposed.
• Charging effects are considered by inputing the Duane–Hunt limit as incident energy.
• Changes in X-ray spectra due to charging were studied by Monte Carlo simulations.
• The methodology has shown to be suitable for the analysis of archaeological pigments.
• It may be applied in forensic or archaeological samples, ancient artwork, etc.

An approach to perform elemental quantitative analysis in a conventional scanning electron microscope with an energy dispersive spectrometer has been developed for non-conductive samples in which the conductive coating should be avoided. Charge accumulation effects, which basically decrease the energy of the primary beam, were taken into account by means of the Duane–Hunt limit. This value represents the maximum energy of the continuum X-ray spectrum, and is related to the effective energy of the incident electron beam. To validate the results obtained by this procedure, a non-conductive sample of known composition was quantified without conductive coating. Complementarily, changes in the X-ray spectrum due to charge accumulation effects were studied by Monte Carlo simulations, comparing relative characteristic intensities as a function of the incident energy. This methodology is exemplified here to obtain the chemical composition of white and reddish archaeological pigments belonging to the Ambato style of “Aguada” culture (Catamarca, Argentina 500–1100 AD). The results obtained in this work show that the quantification procedure taking into account the Duane–Hunt limit is suitable for this kind of samples. This approach may be recommended for the quantification of samples for which coating is not desirable, such as ancient artwork, forensic or archaeological samples, or when the coating element is also present in the sample.