Multicommutated flow-through optosensors implemented with photochemically induced fluorescence: Determination of flufenamic acid

This article describes a multicommutated flow injection-solid phase spectroscopy system implemented with photochemically induced fluorescence for the determination of flufenamic acid (FFA). A strongly fluorescent photoproduct is generated when FFA is irradiated online under UV light in a strong sulfuric medium. The photoproduct generated is retained on C18 silica gel (which fills the detection area of the flow cell) and directly monitored on the active solid support at 258/442 nm (λex/λem). After maximum signal recording, the sensing zone is regenerated by eluting the retained photoproduct with an appropriate H2SO4/MeOH solution. The sensor, completely automated, is based on the use of three-way solenoid valves conveniently operated by a homemade multicommutation software written in Java language. The system is calibrated at 10 and 60 s for sampling time, showing detection limits of 1.28 × 10−9 and 5.33 × 10−10 mol L−1 and sampling rates of 38 and 28 h−1, respectively, with relative standard deviations of 0.9 and 1.2%. The applicability of the method is demonstrated for the determination of FFA in human serum, human urine, and a pharmaceutical preparation without any pre-treatment. Good recovery levels were achieved between 90.5 and 103.7%.