def METHOD_NAME(m, base="ion"):
    """
    Builds NF model based on the IDAES separator for a specified property base.
    Requires prop_ion or prop_salt property package.
    """
    prop = property_models.get_prop(m, base=base)
    m.fs.NF = Separator(
        property_package=prop,
        outlet_list=["retentate", "permeate"],
        split_basis=SplittingType.componentFlow,
        energy_split_basis=EnergySplittingType.equal_temperature,
    )
    # specify
    if base == "ion":
        m.fs.NF.split_fraction[0, "permeate", "H2O"].fix(0.9)
        m.fs.NF.split_fraction[0, "permeate", "Na"].fix(0.9)
        m.fs.NF.split_fraction[0, "permeate", "Ca"].fix(0.1)
        m.fs.NF.split_fraction[0, "permeate", "Mg"].fix(0.1)
        m.fs.NF.split_fraction[0, "permeate", "SO4"].fix(0.1)
        # Cl split fraction determined through electro-neutrality for the retentate
        charge_dict = {"Na": 1, "Ca": 2, "Mg": 2, "SO4": -2, "Cl": -1}
        m.fs.NF.EN_out = Constraint(
            expr=0
            == sum(
                charge_dict[j]
                * m.fs.NF.retentate_state[0].flow_mol_phase_comp["Liq", j]
                for j in charge_dict
            )
        )
        constraint_scaling_transform(m.fs.NF.EN_out, 1)
    elif base == "salt":
        m.fs.NF.split_fraction[0, "permeate", "H2O"].fix(0.9)
        m.fs.NF.split_fraction[0, "permeate", "NaCl"].fix(0.9)
        m.fs.NF.split_fraction[0, "permeate", "CaSO4"].fix(0.1)
        m.fs.NF.split_fraction[0, "permeate", "MgSO4"].fix(0.1)
        m.fs.NF.split_fraction[0, "permeate", "MgCl2"].fix(0.2)
    # scale
    set_scaling_factor(
        m.fs.NF.split_fraction, 1
    )  # TODO: IDAES should set these scaling factors by default
    if base == "ion":
        constraint_scaling_transform(m.fs.NF.sum_split_frac[0.0, "H2O"], 1)
        constraint_scaling_transform(m.fs.NF.sum_split_frac[0.0, "Na"], 1)
        constraint_scaling_transform(m.fs.NF.sum_split_frac[0.0, "Ca"], 1)
        constraint_scaling_transform(m.fs.NF.sum_split_frac[0.0, "Mg"], 1)
        constraint_scaling_transform(m.fs.NF.sum_split_frac[0.0, "SO4"], 1)
        constraint_scaling_transform(m.fs.NF.sum_split_frac[0.0, "Cl"], 1)
    elif base == "salt":
        constraint_scaling_transform(m.fs.NF.sum_split_frac[0.0, "H2O"], 1)
        constraint_scaling_transform(m.fs.NF.sum_split_frac[0.0, "NaCl"], 1)
        constraint_scaling_transform(m.fs.NF.sum_split_frac[0.0, "CaSO4"], 1)
        constraint_scaling_transform(m.fs.NF.sum_split_frac[0.0, "MgSO4"], 1)
        constraint_scaling_transform(m.fs.NF.sum_split_frac[0.0, "MgCl2"], 1)