Direct determination of selenium in sub-milligram amounts of human sperm nuclei by electrothermal atomic absorption spectrometry

In the sperm nuclei selenium is present only in form of a single selenoenzyme, the sperm nuclei glutathione peroxidase (snGPx), involved in processes to secure the structural stability of the nuclear chromatin. As changes in its expression may affect sperm function, its analysis is of interest in the diagnosis of male infertility. A method has been developed which by removal of the other selenium compounds present in other sperm components and measurement of the concentration of selenium in the purified human sperm nuclei by electrothermal atomic absorption spectrometry (ETAAS) allows the quantitative analysis of this enzyme. As the purification resulted in yields in the range of only 150 μg nuclei/ml semen and the amount of purified nuclei in the sample could only be determined by weighing, the main analytical difficulty arose from the accurate determination of the sample masses. The procedure includes preparation of purified sperm nuclei, measurement of the sample mass and direct selenium analysis in the suspensions of the compact sperm nuclei without prior digestion of the matter, using a palladium matrix modifier, a spectrometer with Zeeman background correction and a graphite atomizer with L'vov platform. The detection limit for the determination of selenium was 8.4 pg. The quality control of the results by means of instrumental neutron activation analysis (INAA) showed the reliability of the selenium determination by ETAAS. The procedure proved to be suitable to analyze selenium and thus snGPx in very small amounts of purified human sperm nuclei.