The determination of total protein in plant samples is a difficult task, as classical nitrogen-based methods are not selective for the nature of nitrogen, and the results of biochemical methods are influenced by both associated compounds and the complex composition of the protein matrix. Using electrophoretic separation of three commercial sunflower protein samples, it was determined that the studied proteins are a mixture of salt-soluble globulins and water-soluble albumins of different molecular weights. The total protein content of the studied samples was determined using five spectrophotometric methods: direct spectrophotometry, bicinchoninic acid assay, and Benedict’s, Bradford’s, and Lowry’s methods. After comparing the results obtained, it was concluded that, for the determination of protein in these plant materials, the use of the Dumas nitrogen-based method in tandem with Lowry’s spectrophotometric method is the most suitable.

X-ray fluorescence is one of the best approaches for nondestructive elemental analysis and is consequently widely used in industry and science. Among the main problems for its application are matrix effects and a significant content of unidentified undetectable light elements, which influence the results and may be difficult to take into account. Several approaches have been proposed for solving these problems, including those based on the use of intensity ratios and the primary radiation scattered by the sample, which often allow one to achieve satisfactory accuracy using only a few reference samples. The goal of this review is to compare these approaches, discuss their advantages and disadvantages, and highlight the prospects for their further development.