Evaluation of energy dispersive X-ray fluorescence and total reflection X-ray fluorescence spectrometry for vegetal mass-limited sample analysis: Application to soybean root and shoots

Proper supply of nutrients to plants is mandatory for adequate crop production. Many strategies, such as soil fertilization, nutrient foliar spraying, and seed treatment have been proposed to this goal. Currently, plenty of studies in plant nutrition afford only a low mass of sample for analyses, which is not sufficient for most spectroscopic techniques, including conventional energy dispersive X-ray fluorescence spectrometry (EDXRF). In this context, we developed a new EDXRF method for the determination of nutrients in mass-limited soybean plant tissues. Soybean seeds were treated with different types of Zn suppliers (ZnSO4 and ZnO nanoparticle sources), sowed, and soybean roots and shoots were sampled two weeks after germination. For EDXRF analysis, 20 mg of samples were suspended in 1 mL of deionized water, and 20 mu L of the suspension were dried on a 6 mu m polypropylene film in an X-ray cup. External calibration using a set of synthetic aqueous cellulose multielemental standards suspended in 1% Triton X-100 proved to be a good strategy for quantification purposes. The trueness of the proposed method was verified analyzing several plant tissue certified reference materials. Additionally, soybean samples were also analyzed by using a validated total reflection X-ray fluorescence (TXRF) method, and good agreement was found between both analytical approaches. To sum up, the proposed EDXRF thin film method is straightforward and reliable for mass limited vegetal sample multielemental analysis and, additionally, follows the green analytical chemistry postulates.