Resonance Rayleigh scattering approach based on association complex formation with erythrosine B for determination of venlafaxine, application to the dosage form and spiked human plasma.

The interaction of venlafaxine hydrochloride (VLX) with erythrosine B was investigated using a resonance Rayleigh scattering (RRS) spectroscopic technique. In acetate buffer (pH 3.4), erythrosine B reacted with VLX to form a 1:1 ion-pair complex with concomitant enhancement in RRS intensity that was measured at 330 nm. In addition, the stability constant and the change in free energy of the reaction were estimated. Based on this interaction a new method was developed for a sensitive VLX analysis using erythrosine B as a probe. The results indicated that this method had good selectivity in the presence of coexisting compounds. The scattering intensity (ΔI ) was linearly dependent on VLX concentration over the range 0.04-1.0 μg ml with a determination coefficient (r) of 0.9998. The limit of detection and limit of quantitation were 0.01 and 0.03 μg ml , respectively. This method could be suitably used for analysis of VLX in pharmaceutical capsules and human plasma.