Potentiometric determination of acetylsalicylic acid by sequential injection analysis (SIA) using a tubular salicylate-selective electrode

This paper deals with the development of an automated procedure for formula tion assays and dissolution tests based on a sequential injection analysis (SIA) system involving an ion-selective electrode as sensing device. Constr uction of a tubular salicylate (Sal) selective electrode suitable for poten tiometric determination of acetylsalicylic acid (Asa) in pharmaceutical for mulations is described. The flow-through electrode is formed by a PVC membr ane containing 29.2% (w/w) PVC, 5.8% (w/w) tetraoctylammonium salicylate (i onic sensor), 58.5% o-nitrophenyloctylether (plasticizer) and 6.5% (w/w) p- tert-octylphenol (stabilising, additive which increases electrode selectivi ty). The calibration range is 0.05-10 mM Sal, the limit of detection (LOD) is 0.05 mM Sal, the slope is 56.0 mV per decade at 22 degreesC. The R.S.D. is 0.20% (15 readings) when determining 2.5 mM Sal in standard solution. Th e electrode is used fur sensing Asa after. its on-line chemical hydrolysis to Sal in a SIA system. The sampling rate is 6 h(-1) but for the dissolutio n tests the frequency is increased to 20 h(-1). The SIA set-up is employed for the assay of Asa in plain tablets, composed tablets and effervescent ta blets and for performing dissolution tests of normal and sustained release tablets. Results obtained by this technique compare well with those require d by the US Pharmacopoeia XXIV. (C) 2001 Elsevier Science B.V. All lights r eserved.