G. Papeschi

Potentiometric titration of thiols, cationic surfactants and halides using a solid-state silver—silver sulphide electrode

A rugged, low resistance silver-silver sulphide solid-state electrode for determining pharmaceuticals as authentic samples or in dosage forms by potentiometric titration is described. Sodium tetraphenylborate, mercury(II) acetate and silver nitrate (0.01) M were employed as titrants in the analysis of cationic surfactants (cetylpyridinium chloride, benzethonium chloride, benzalkonium chloride and chlorhexidine salts), antithyroid drugs (methimazole and propylthiouracil) or sodium halides respectively.

Chlorhexidine loss from simulated contact lens solutions stored in glass and plastic packages.

A storage test on chlorhexidine gluconate (0.004%) in aqueous or simulated contact lens solutions, conducted for 6 months in various containers, suggested [l] that loss of activity by a surface adsorption process was occurring. It has been reported [2] that contact lens solutions containing chlorhexidine gluconate (0.~5%) stored at room temperature in the dark for 6 months in polypropylene, polyethylene, and amber and clear glass, showed an antiseptic loss of 4-10% in plastic containers and, unexpectedly, of 16% and 25% in amber and clear glass respectively. However, the type of glass employed was not stated. More recently [3], storage experiments on ophthalmic drops containing benzalkonium chloride or chlorhexidine acetate indicated no adsorption by glass or ~lyethylene containers. The calorimetric method [4] used in this case for assaying the preservatives has been criticized as yielding large errors [5] and as unsuitable for the determination of chlorhexidine salts [6]. Chlorhexidine gluconate (O.OOl-0.006%), combined with benzalkonium chloride or thiomersal, is widely employed as a preservative in contact lens solutions. These solutions are ~mmonly packaged in polyolefin containers and many regulatory authorities demand that there should be no container-preservative interaction. Recently the present workers described [6] a rapid and reliable calorimetric method for determining chlorhexidine gluconate in commercial contact lens solutions through the formation of a stable ion-pair with methyl orange. The ion pair can be extracted with chloroform without interference from other ingredients or from 4-chloroaniline, the main breakdown product of chlorhexidine. The present paper reports the application of

Differential-pulse adsorptive stripping voltammetry of chlorhexidine

Chlorhexidine gluconate was shown to adsorb onto a hanging mercury drop electrode and to be amenable to quantification by adsorptive stripping voltammetry. A sensitivity of 1 × 10–7 mol dm–3 was easily achieved by simply immersing the electrode in a stirred solution (pH 9.7 ammonia-ammonium acetate buffer) of the drug for a fixed time (60 s), at a suitable potential (0.0 V versus Ag–AgCl), and then stripping cathodically in the differential-pulse mode. The stripping peak potential was –1.53 V. Cyclic voltammetry was used to test the interfacial and redox behaviour. Chlorhexidine gluconate was assayed in mouthrinse and contact lens solution dosage forms.

Differential pulse polarographic determination of total benzophenantridinium alkaloids in Sanguinaria extract-based oral rinses

A differential pulse polarographic method was developed for the determination of total benzophenantridinium alkaloids in Sanguinaria canadensis extract-based oral rinses without prior extraction procedures, Mcllvaine buffer (pH 3.4) being employed as the supporting electrolyte. The electrochemical reduction involves the transfer of one electron and potential of the single peak occurs between − 0.39 and −0.44 V vs Ag/AgCl as a function of the different relative percentage of benzophenantridinium alkaloids. The alkaloid amount was expressed as chelerythrine chloride and calculated by means of a calibration graph. A column Chromatographie procedure to obtain chelerythrine chloride reference standard is described. Common oral rinse excipients and zinc ions were found not to interfere.

Evidence of silver(I) adsorption processes on the electroactive surface of the silver/silver selenide electrode

Abstract A silver(I) ion-selective electrode, based on the silver selenide formed by cathodic deposition of selenium directly onto a silver substrate, is described. The deposition is carried out at a density current of 2 mA cm −2 from 0.1 M Na 2 SeO 3 solution whose pH is decreased to between 5 and 6 with either sulphuric or hydrochloric acid. Experimental results about the adsorption process of silver(I) ions on the electroactive surface of the Ag/Ag 2 Se electrode are discussed. In order to measure the silver(I) release or uptake of one Ag/Ag 2 Se electrode, a second Ag/Ag 2 Se electrode previously stabilized in the base electrolyte is used as a measuring electrode in the same solution.

Copper(II) ion-selective sensor with electrolytically plated chalcogenide coating

Abstract The performance characteristics of a copper(II) ion-selective electrode, based on the copper selenide formed by cathodic deposition of selenium directly onto a copper substrate, are reported. The deposition is carried out at a constant current of 2 mA/cm2 from 0.1 M Na2SeO3 solution whose pH is adjusted to between 6 and 4 with either sulphuric or hydrochloric acid. The electrodes exhibit a linear Nernstian response down to 10−5 M copper(II) in non-buffered medium. Data on the electrode response time and pH dependence are also presented.

Reliability of polarographic method in measurement of contact lens oxygen permeability

Accurate and precise contact lens oxygen permeability (Dk) measurements are obtained with the polarographic method if: 1 the electrode head is kept clean and dry between measurements, 2 a check is kept that there is only the minimum saline solution necessary between lens and electrode, 3 humidity is kept constant with a sponge soaked in water underneath the special chamber cover, especially for soft lenses, 4 the lens thickness is measured with great accuracy. In fact small errors (10 pm) in thickness measurement result in significant error (1 unit) in Dk value.