Partial least squares modelization of energy dispersive X-ray fluorescence.

As a proof of concept, a green methodology has been developed for the energy dispersive X-ray fluorescence (ED-XRF) determination of calcium, potassium, iron, magnesium, aluminum, chromium, strontium, phosphorus and nickel in the peel of untreated kaki fruit (Diospyros kaki. L) samples. ED-XRF spectra of fifty-six kakis purchased in the local area of LLombay (Valencia) were obtained directly from samples without any previous treatment and without sample damage just after cleaning the fruit with distilled water. Inductively Couple Plasma Optical Emission Spectrometry (ICP-OES) was used as a reference method to determine the mineral elements after microwave assisted acid digestion. XRF spectra and concentration values obtained by ICP-OES were processed using partial least squares (PLS) data treatment to build the corresponding chemometric models for prediction of mineral profile of samples. PLS-ED-XRF permits a direct and accurate determination of Ca and K in kaki peel. For Al, Fe, Mg, Ni and Sr screening semiquantitative results were obtained. Concentrations obtained directly by the internal calibration of instrument, using GeoChem Trace model, were also compared with data predicted by chemometric models being found that PLS models must replace the calibration of the instrument for thus kind of analysis.

Direct determination by portable ED-XRF of mineral profile in cocoa powder samples.

The present study has exploited the rapidity of the analysis and the multi-elemental capability of the energy dispersive X- ray fluorescence (ED-XRF) technique for the mineral profile determination in cocoa powder. A fast, cheap and environmental sustainable method without reagent consumption or toxic waste generation has been proposed. The samples can be prepared in the form of pellets of 13 mm in diameter and 2-3 mm thickness. The different internal calibrations used by ED-XRF equipment did not provide accurate results when comparing the mineral profile with the concentration obtained by Inductively Couple Plasma Optical Emission Spectroscopy (ICP-OES) after microwave assisted digestion of samples. For direct ED-XRF analysis of the cocoa samples, an external calibration using as standards the cocoa samples diluted with sugar was prepared. The analytical parameters of Relative Standard Deviation and Limit of Detection for the determined elements are adequate to the concentration levels found in the samples.