A method for urinary iodine diagnostics using a portable energy-dispersion X-ray fluorescent (EDXRF) spectrometer is proposed. The principle of the method consists in excitation of the sample atoms fluorescence by the energy spectrum intentionally formed from the spectrum of an X-ray tube using an optimized X-ray scheme. The optimization by the criterion of the minimum detection limit for L-series iodine fluorescence lines included the calculation of optimal atomic numbers for materials of a

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... radiator and a filter, and their thicknesses, the collimation system parameters, and an X-ray tube voltage. Experimentally achieved detection limits were 45 and 75 g/L by I-L␣ and I-L␤ lines, respectively, at the theoretically extreme value 30 g/L. This sensitivity is found to be sufficient for urinary iodine diagnostics in the range from 50 to 200 g/L. The results obtained from different patients have shown the satisfactory convergence for the iodine concentration determination by L␣ and I-L␤ fluorescence lines. The simple sample preparation procedure and comparably small sizes of the apparatus allows rapid researches directly in clinical settings.