Determination of Doxepin hydrochloride from spiked human plasma and capsule after derivatization with Eosin Y using Resonance Rayleigh Scattering, Second Order Scattering, and Frequency Doubling Scattering Methods.

Doxepin hydrochloride is a tricyclic antidepressant drug. Three sensitive spectrofluorimetric methods based on the Resonance Rayleigh scattering (RRS), Frequency Doubling Scattering (FDS) and Second Order Scattering (SOS) were developed and validated for their estimation of doxepin in spiked human plasma and formulation using liquid-liquid extraction method through the formation of an ion pair complex with eosin Y at pH 4.5. Various factors affecting fluorescence intensity were optimized, and the reaction kinetics was determined using the Arrhenius equation method. Different scattering methods RRS, FDS, and SOS were developed at maximum scattering wavelengths, λ ex /λ em being 567/567nm for RRS, 720/360nm for SOS, and 260/520nm for FDS, respectively. The methods exhibited high sensitivities, the detection limits for DOX were found to be 0.82 ng/ml,1.20 ng/ml, and 1.03 ng/ml for RRS, FDS, and SOS methods respectively. The FDS method displayed the highest sensitivity. The methods were validated using ICH guidelines and applied to determine DOX in capsule and spiked human plasma samples.