Dielectric measurements of aqueous solutions at low frequencies below 104–105Hz have always been accompanied by two problems, which have made it difficult to obtain precise results; they are (i) the electrode polarization and (ii) the thermal drift of electric dc conductivity. For the former, adoption of a four‐electrode cell has been proven to be effective in suppressing the electrode polarization. For the latter problem, a time domain measurement of the dielectric spectra is adequate. A combination of a four‐electrode method with a time domain spectrometry using a Fourier synthesized pseudorandom noise (FSPN) method gave precise dielectric spectra at low frequencies, which were difficult to obtain by previous methods, with an adequate reproducibility for aqueous solutions of biological molecules, DNA, and polyglutamic acid. A precise description of the combined system is mentioned and the precision of the measurement is discussed.
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