Fast determination of salicylic acid in pharmaceuticals by using a terbium-sensitized luminescent SIA optosensor

In this article, we report the coupling of sequential injection analysis (SIA) and solid phase lanthanide-sensitized luminescence as a detection technique; in this technique, the energy absorbed by the analyte (retained on a solid support) is transferred to the lanthanide ion, which finally emits the luminescence signal. By using this automatic system, the determination of salicylic acid (SA) is easily, rapidly, and selectively achieved. Microspheres of commercial solid support, Sephadex-QAE A-25, are used to fill the flow-through cell and retain analyte and terbium ions; after the signal from SA-terbium complex is obtained, the solid support is easily regenerated by using an ethylenediaminetetraacetic acid disodium salt 2-hydrate (EDTA) solution. Over 200 determinations can be carried out without replacing the resin microbeads. The proposed method shows a 0.045 microg mL(-1) detection limit, with an R.S.D. lower than 3% and a sampling frequency up to 30 samples per hour. The system has been applied to the determination of SA in pharmaceuticals obtained from the Spanish Pharmacopoeia, with satisfactory results; an additional recovery study has been carried out with recoveries close to 100%.