Construction and Evaluation of Scopolamine Ion-Selective Electrode

The coiistniction of plasticised PVC matrix-type scopolamine ionselective ineinbrane electrode and its use in tlie potentioinetric detenninatioii of scopolainine in pliannaceutical preparations are described. It is based on the use of tlie ion-associate species, fonned by scopolainine cation and 5-nitrobarbitoric counter ion. The basic electrode peifonnance characteristics are evaluated according to IUPAC I-ecoininendatioiis. It exhibited a linear response for 1 x 1 o ' ~ -1 x10" M of scopolainine solidions witli a catioiiic Nernstian slope over the pH range of 4 Coininon organic and inorganic cations showed negligible interference. Direct potentioinetric detenninatioii of 1 x 1 0-' 1 x 1 0" M aqueous tuboctirarine chloride using this ineinbrane electrode systein sliowed ail average recovery of 99.05 witli a inean standard deviation of 0. I . This electrode system was successfillly applied to tlie potentioinetric detenninatioii of scopolainine in some pliannaceutical preparations. Kc)! wordv : Scopolamine ineinbrane electrode, potentioinetry , phannaceutical analysis. A. S h a I a b y et al.:


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In this paper, attempt has been made to develop a simple potentio~netric ~netl~od using a PVC membrane electrode responsive for scopolainine botylbro~nide with sufficiently high accuracy, selectivity and speed.

Reagents:
All chemicals were of analytical-reagent grade and solutions were prepared with de-ionised water.Poly (Vinyl chloride) (PVC), tetrahydrofitran.dioctylpl~thalate and 5-nitrobarbitl~ric acid were obtained from Signa chemical Co. Scopolamine butylbrolnide and its pharmaceutical preparations were obtained from Chemical Industries Developinent Co., (CID) Egypt.

Sensor Preparation:
The scopola~nine-5-nitrobarbiturate was prepared by mixing 20 1n1 of I M aqueous scopolamine butyl bromide with 20 in1 of 1 M ethanolic 5nitrobarbituric acid solution '47'.After stirring for 15 inin., the yellowish precipitate was filtered off on a porosity-3 sintered-glass crucible, washed twice with doubly distilled water, followed by ethanol, dried at 100" C for one hour, then ground to fine powder.Eleinental analysis and the infrared spectra of the products confinned that 1 : I compounds had been fonned.(Fig. 1 )

Effect of pH:
The effect of pH on the potential of the electrode system was studied iising two pH/mV meters.The combined glass caloinel electrode \\.as connected to one instn~inent and the PVC scopolainine membrane with the double junction AdAgCl reference electrode was connected to the second instiuinent. 30in1 aliqt~ots of 1 x 1 o", 1 x 1 o-' and 1 xl0" M scopolamine butyl broinide were trailsferred to a 100 in1 beaker where the three electrodes were immersed, the potential reading corresponding to different pH values were recorded.The pH was gradually increased or decreased by the addition of sinall aliquots of dilute solutions of sodium hydroxide or hydrochloric acid respectively and the inV-pH was plotted.

Interference Effects:
The response of the electrode was also examined in the presence of a nuinber of organic and inorganic ions.The potentiometric selectivity were used to evaluate the degree of interference .coefficients $cop+.Where E l and E2 are the potential readings observed after one minute due to the same concentratioil of scopolainine butylbroinide and the interfereots respectively and S is the slope of the scopolainine calibration ~~~a p h (mV/concentration decade).Scop' is the abbreviation of scopolainine.
For all the previous filial diluted solution the pH was adjusted to pH 1-7.The PVCscopolamine-5-nitrobarbiturate membrane electrode and an Orion double-junction Ag-AgC1 reference electrode were immersed in the solution.The electrode system was allowed to equilibrate with stirring aiid tlie e.1n.f was recorded aiid compared with tlie calibration graph.

Nature and response characteristics of the Electrode:
Scopola~nine reacts with hitrobarbituric acid to fonn a water insoluble scopolalnine complex.The electrochemical performance characteristics of this electrode system were evaluated according to Tlie dynainic respoiise time of tlie electrode system was tested for  separate solutions metl~od ' "" " '.' ' with lo-' M concentration of both the standard scopola~nine and the interferents.The results obtained, table 2 sliows reasonable selectivity for scopolamine in the presence of inany interferents.In most cases, no significant influence on the electrode Direct potentioinetric determination of scopolainine butyl bromide using tlie scopolamine 5-nitrobarbiturate-PVC membrane electrode was perfonned and calcl~lated fioin the calibration curve.The statistical data of the analytical reslllts obtained by the proposed method and the official inetl~od'~'' for tlie tested dnlg in pure fonn has been illustrated in table (3).
The results obtained by both ~netliods are approxi~nately in good agreement, however, the electrode neth hod offers several advantages in tern1 of si~nplicity, selectivity, less time consuming aiid precision.Further, the results obtained were encouraging to apply the proposed method for tlie detenninatioil of scopolainiiie botylbroinide in some pliannaceutical preparations.The results listed in table (4), show agreement with those g i ~e n with the official inetliods.Tl~us it is recoinine~~ded for the precise direct poteiitioinetric assay of scopolainine butyl bromide in pure fonn and ill phannaceutical preparations.
scopolainine butyl bromide solutions.Tlie ineaslire~nent sequence was froin low concentration to tlie higher_ and back.The required time for the electrode to reach values within k 0.5 inV fioin the fiilal equilibri~lin potential after illcreasing the scopolainine btityl bromide concentration level to 10 fold is fairly short, it reaches 90% of its final stead?! potential after 15 sec.

N=Table 4 :
Number of experiments S .D .= Standard deviation S. E. = Standard error F = Variance test t = t test of unpaired data Comparative analytical results of the proposed and official method for the scopolamine in some pharmaceutical preparations.