Dielectric analysis of aqueous poly(l-glutamic acid) and poly-l-(glutamic acid4, Tyrosine1) solutions at high frequencies from capacitance measurements

A new parallel-plate capacitor fixture has been designed and successfully used to measure dielectric loss of polyelectrolyte solutions with volumes as low as droplets of 13-26 μL. It is particularly useful when studying polypeptides that are either high-cost or can be synthesized only in limited quantities. The ease with which the fixture can be used to obtain preliminary dielectric loss data yields savings in time and cost. In this study capacitance measurements were performed in a wide range of frequencies between 1 and 800 MHz using an Agilent 4191RF Impedance Analyzer. Accuracy of measurements was carefully examined through a comparison of measured conductivity of 1M NaCl against Stogryn's equation for conductivity. A 0.3% difference between the experimentally measured and theoretically calculated results has been found, demonstrating the validity of the proposed analysis method.