Automated sequential injection fluorimetric set-up for multiple release testing of topical formulation

A fully automated sequential injection analysis (SIA) device for simultaneous release testing of multiple ointment samples was devised and applied to the release testing of an ointment containing salicylic acid as an active substance. The SIA system consisted of a bi-directional 5 ml syringe pump, two 8-position selection valves, auxiliary peristaltic pump, fluorescence detector and three Franz cells maintained at 32 °C (water bath). The ointment sample was placed on top of a synthetic Millipore GTTP poly(carbonate) membrane (thickness 10 μm, pore size 0.2 μm) of the Franz cell containing 15 ml of aqueous phosphate buffer of pH 7.4 as the acceptor liquid. The samples of the acceptor liquid (50 μl) were aspirated in 15 min intervals for the period of 6 h from each of the 3 cells and dispensed to a fluorescence detector to determine the concentration of salicylic acid (excitation at 297 nm and emission at 405 nm). The volume of the acceptor medium taken for analysis was automatically replenished after each measurement. The calibration curve was rectilinear for 1-100 μg ml−1 of salicylic acid. The device allowed simultaneous monitoring of the release tests for up to six cells including automated computer-aided evaluation of the release profile parameters.