This work measured relative permittivity from 15.0 to 55.0 °C of aqueous solutions containing acetone or tetrahydrofuran using a BI 870 dielectric meter. A cubic polynomial fit resulted in coefficients for calculating permittivity as a function of temperature and mole fraction. Literature values for other co-solvent system resulted in similar polynomial coefficients. Using BI 870, permittivity measurements of ionic solutions were not possible because of high conductivity. A simple method using impedance spectroscopy measured these solutions. Impedance decreases with increasing temperature and decreases with increasing ionic strength. Due to the temperature dependence of impedance, all measurements were at 25.0 °C. Anions including bicarbonate, sulfate, acetate, and carbonate were determined using this method. Detection limits were at parts per trillion (ppt) levels. A simple sensor based on smaller stainless steel cylinders and a circuit to determine impedance is currently being developed in combination with an anion exchange column.