A new technique to produce isobarically pure ion beams for decay spectroscopy by using a gas-filled Penning trap was commissioned at the ion guide isotope separator on-line facility, IGISOL. β-decays of neutron-rich 100Zr, 102Zr and 104Zr isotopes were studied with this technique. In addition, the $\ensuremath Q_{\beta^{-}}$ values of 100,102,104Zr β-decays were determined from the direct mass measurements of zirconium and niobium isotopes performed with a high-precision Penning trap. The mass of 104Nb was directly measured for the first time and the obtained mass excess value for the longer-living (1+) state is -71823±10 keV. For the ground states of 100Nb and 102Nb the obtained mass excess values were -79802±20 keV and -76309±10 keV, respectively. The observed distribution of the β strength supports a prolate deformation assignment for 100,102,104Zr isotopes.