Tropane alkaloids, especially hyoscyamine and scopolamine, are widely used in medicine because of their strong parasympatholytic actions. Recently, it has been demonstrated that the alkaloid pattern can be shifted towards scopolamine when introducing the 6h6 gene which is involved in the biosynthesis of scopolamine from hyoscyamine.1,2 Scopolamine is a tropane alkaloid from solanaceous plants, and is used as an anti-convulsant, an anti-emetic, and an anti-parkinsonism; sedative-scopolamine was also evaluated as possible diagnostic agents for dementia.Several analytical techniques have been reported for the quantitative determinations of scopolamine. Among these are high-performance liquid chromatography (HPLC), 3-5 capillary zone electrophoresis, 6 proton nuclear-magnetic resonance spectroscopy, 7 gas chromatography mass-spectrometry (GC-MS), 8 micellar electrokinetic chromatography, 9 enzymeimmunoassay, 10 and potentiometry. 11 Most of these methods involve several time-consuming manipulation steps and require sophisticated instruments.Potentiometric methods using ion-selective electrodes have found wide application, 12-16 being simple, economical, and applicable over a wide range of different areas, and offer sufficient selectivity towards the drug in the presence of various pharmaceutical excipients. 17 A membrane electrode for the determination of scopolamine using scopolamine-tetraphenylborate 11 as an electroactive material was reported. The response of the electrode was linear for 0.02 -100 mmol dm -3 , with a response time of 15 s with a detection limit of 4 µmol dm -3 .The present work describes the preparation, characterization and some possible applications of a novel scopolamine PVC sensor based on the use of a scopolamine-phosphotungstate ionpair complex as the electroactive material and dioctylphthalate or o-nitrophenyloctyl ether as a placticizer. The sensitivity and stability offered by this simple electrode configuration are sufficient high to allow an accurate determination of low levels of scopolamine. Selectivity coefficient measurements by many cations and anions are negligibly small.
ExperimentalApparatus All potentiometric measurements were made at 25 ± 1˚C, unless otherwise stated, using an Orion pH/mV meter (Model 330). A combined Ross glass pH electrode (Orion 81-02) was used for pH measurements. An Orion double-junction Ag-AgCl reference electrode (Model 90-02) containing 10% (w/v) potassium nitrate in the outer compartment was used.
Reagents and materialsAll chemicals used were of analytical reagent grade, unless otherwise stated. Doubly distilled water was used throughout. Polyvinyl chloride powder (PVC) of high molecular weight, dioctylphthalate (DOP), o-nitrophenyloctyl ether (ONPOE), and tetrahydrofurane (THF) of purity >99% were obtained from Aldrich Chemical Company. Scopolamine hydrobromide, sodium tetraphenylborate, and phosphotungstic acid were obtained from BDH. Scopolamine injection (1 mg/cm 3 ) and ophthalmic solutions (0.25%) were obtained from Ciba Vision (Niederwagen, S...