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Microbeam X-ray spectrometry, energy-dispersive X-ray fluorescence analysis, and neutron activation analysis were evaluated for the detection of selenium contained in the selenoprotein glutathione peroxidase. The glutathione peroxidase had been previously separated using polyacrylamide gel electrophoresis. The use of Bragg-reflected polarized X-ray beams was employed in the X-ray fluorescence measurements to minimize the problem of scatter owing to the gel matrix. Current detection limits of selenium in a gel matrix are 2.1 ng in the bench-top microbeam X-ray system and 30-60 ng using XRF with polarized beams. Neutron activation analysis was used for quality-control measurements, with a detection limit here of < 0.08 ng. The work has in principle established the feasibility of such an approach.