Direct determination of mineral nutrients in soybean leaves under vivo conditions by portable X-ray fluorescence spectroscopy

A portable energy dispersive X-ray fluorescence (XRF) spectrometer furnished with an Rh X-ray tube was evaluated for the determination of macronutrients and micronutrients in soybean leaves (Glycine max L.). XRF instrumental parameters were optimized in a univariate way, and emission intensities were measured for 60 s and under vacuum for macronutrients, and during 180 s, under air, and 305 mu m Al/25.4 mu m Ti filter, for micronutrients. Fresh and dried leaves were irradiated, and it was possible to identify P, K, Ca, S, Mn, Fe, Cu, and Zn K alpha emission lines. For comparative purpose, the samples were also microwave assisted, digested and analyzed by inductively coupled plasma optical emission spectrometry. In general, linear correlations between K, Ca, Mn, Fe, Cu, and Zn concentrations in the tested samples and the corresponding portable XRF (pXRF) intensities were obtained. The linear correlation coefficients (R-2) ranged from 0.42 to 0.86. In addition, the detection limits were suitable for plant nutrient diagnosis. It is demonstrated that pXRF is a simple and powerful tool for analysis of plant materials.