New Conventional Coated-Wire Ion-Selective Electrodes for Flow-Injection Potentiometric Determination of Chlordiazepoxide

Abstract

New chlordiazepoxide hydrochloride (Ch-Cl) ion-selective electrodes (conventional type) based on ion associates, chlordiazepoxidium-phosphomolybdate (I) and chlordiazepoxidium-phosphotungstate (II), were prepared. The electrodes exhibited mean slopes of calibration graphs of 59.4 mV and 60.8 mV per decade of (Ch-Cl) concentration at 25˚C for electrodes (I) and (II), respectively. Both electrodes could be used within the concentration range 3.16 × 10 -6 -1 × 10 -2 M (Ch-Cl) within the pH range 2.0 -4.5. The standard electrode potentials were determined at different temperatures and used to calculate the isothermal coefficients of the electrodes, which were 0.00139 and 0.00093 V ˚C -1 for electrodes (I) and (II), respectively. The electrodes showed a very good selectivity for Ch-Cl with respect to the number of inorganic cations, amino acids and sugars. The electrodes were applied to the potentiometric determination of the chlordiazepoxide ion and its pharmaceutical preparation under batch and flow injection conditions. Also, chlordiazepoxide was determined by conductimetric titrations. Graphite, copper and silver coated wires were prepared and characterized as sensors for the drug under investigation.

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“…The influenceo fs omee xcipients, inorganicc ations,a mino acidsa nd sugars on the response of bromhexinium electrodes wasi nvestigatedi nF IA andb atch conditions applying separate solution method as previously described [25].…”

“…The selectivity mechanism is mainly based on the sterospecificity and electrostatic environment, and is dependent on how much fitting is present between the locations of the lipophilicity sites in the two competing species on the bathing solution side and those present in the receptor of thei on-exchanger [25].I no ther words, thed istributiono ft he active components situated at theelectrode surfaceallow theprimary ions to reactbut do notenter the membrane phaseu nder zero-current conditions andt hise xplained thef actt hatt he electrodes urface is notc ompletelyf latb ut hasd epressions andh ills [26]. …”