[en] Technetium-99 concentrations in environmental samples are usually very close to or under the detection limit of a radiation counter. In recent years, ICP-MS has been popularized to measure low ⁹⁹Tc concentrations. Besides, the method is useful to check the concentration of determined ⁹⁹Tc by a radiation counting method. Thus, in this study, ICP-MS has been used to re-measure ⁹⁹Tc in samples prepared for a radiation counting technique. Subjected ⁹⁹Tc sources were planchet samples on which Tc was electroplated after chemical separation from algae. The ⁹⁹Tc activities were previously determined by radiation counting. Tc was continuously removed from each planchet sample with 2M HNO₃ and 2M NaOH. During the first Tc dissolving step from the planchet with 2M HNO₃, a small amount of Tc, which was thought to be fixed as TcO₂, was dissolved. However, additional two extraction steps increased the percentage of extracted Tc to 93 - 97%. After the solution containing Tc was adjusted to 0.1M HNO₃, Tc was extracted on a TEVA resin to concentrate Tc and to remove Ru. It was found that Tc was completely separated from Ru in the final solution for ICP-MS by our separation method. Thus, the isotope, whose mass was 99, could be identified as ⁹⁹Tc. The results of ⁹⁹Tc measurements by both radiation and ICP-MS methods agreed well with each other. The total recoveries for Tc on the planchet samples were almost the same, with an average of 91%. (author)