[en] The chemical effects of isomeric transition of ⁹⁵sup(m)Tc have been investigated in solid lithium, potassium and ammonium pertechnetate matrices. The retention of ⁹⁵gTc in NH₄⁹⁹sup(()⁹⁵sup(m)sup())TcO₄ was about 60% and in Li⁹⁹sup(()⁹⁵sup(m)sup())TcO₄ and K⁹⁹sup(()⁹⁵sup(m)sup())TcO₄ higher than 70%. The unretained ⁹⁵gTc was found preponderantly as a cationic and an uncharged species. Under corresponding storage conditions the retentions for Li TcO₄ were higher than for KTcO₄. The influence of temperature and ambient atmosphere was studied. The samples stored in vacuum showed a higher retention than those kept in air. Thermal annealing leads to an increase in retention. (orig.)