[en] After developing a ³He/⁴He dual beam collection system for the mass spectrometer, the isotopic fractionation factor was determined for helium dissolved in H₂O, D₂O, seawater and ethanol. In all solvents the temperature dependence of the fractionation is different from that for a simple isotope vapor pressure effect. Addition of salt to H₂O increases the fractionation, and the relative salting-out coefficient changes with temperature. A double isotopic effect occurs - the fractionations in D₂O and H₂O differ. In ethanol the fractionation is 25% less than in H₂O