Microwave dielectric relaxation spectroscopy of paracetamol and its aqueous solutions

The complex dielectric function epsilon *(omega) = epsilon' (omega) - j epsilon '' (omega) is studied for aqueous solutions of Paracetamol (PCM) (at four different temperatures 293.15 K, 303.15 K, 313.15 K and 323.15 K) across the frequency range of 200 MHz to 30 GHz and of pure PCM in pellet form (at a constant temperature of 300.15 K) over the frequency ranging from 200 MHz to 20 GHz. Dielectric properties are measured using Anritsu Shockline Vector Network Analyser (VNA) Model No. MS46322A, SPEAG DAK - 1.2 (5-50 GHz) and DAK - 3.5 (200 MHz-20 GHz) probes. Obtained dielectric data are further analysed with Debye relaxation model in order to understand the dipolar relaxation behaviour of these solutions. From obtained dielectric data; other parameters like power reflected (P-r), power transmitted (P-t), penetration depth (d(p)) have also been determined at 2.45 GHz and analysed in view of its applicability for microwave dielectric heating in pharmaceuticals. Temperature dependence of the dipolar relaxation time is used to evaluate thermodynamical parameters: Gibbs free energy of activation (Delta F-e), entropy of activation (Delta S-e) and enthalpy of activation (Delta H-e). (C) 2020 Elsevier B.V. All rights reserved.