Validation of an Energy Dispersive X-Ray Fluorescence method for small sample intake in a wide range of matrices. Application to the analysis of saffron

Abstract

Multi-elemental analyses using Energy Dispersive X-Ray Fluorescence have proven their efficacy in food authentication, but sample intake can be a drawback in the analysis of expensive matrices such as saffron. In this work, small sample holders and the double pellet method (a thin sample layer on a wax pellet) were combined to determine 19 elements of interest in food analysis, using only 1 g of sample. The trueness of these two approaches was evaluated with 17 different organic matrix reference materials of lichen, wheat flour, rice flour, bran, brown bread, cabbage, vegetable feed, pine needles, and spinach, tomato and tobacco leaves. In the analyses of reference materials, double pellets provided accurate results (recovery 100%) for Mg, Al, Si, P, Cl, S, K, Ca, Cr, Mn and Fe, but the penetration of the radiation into the wax layer of the double pellet hindered quantitative recovery for heavier elements. Contrarily, small sample holders were less accurate for the very light elements (Mg, Al and Si) but the recovery was satisfactory (> 80%) for the remaining ones, including the heavier elements (Cu, Zn, Rb, Sr, Cd and Ba). Ni and Br determinations were affected by a possible matrix dependent interference. With some few exceptions, the precision and the limits of quantification for the different elements in saffron, are comparable to those that characterise the analyses with standard pellets. The method was validated to analyse 21 Iranian saffron samples collected on the EU market.