We developed and characterised two membrane ion-selective electrodes, one of them with PVC matrix (I) and the other one with liquid membrane (II), both using atropine tetraphenylborate as electroactive material. These electrodes were used in order to quantitatively determine atropine sulphate from vegetal and pharmaceutical products, as well as total alkaloids expressed as hyoscine from vegetal products.

Studied electrodes present the following functional characteristics:

• both electrodes have a linear response for atropine sulphate concentrations in the range of 10^-5 M - 10^-2 M;
• the detection limit is 3.29·10^-6 M atropine sulphate for electrode (I) and 2.83·10^-6 M for electrode (II);
• the electrodes' slopes are 39.65 mV/decade (I) and respectively 44 mV/decade (II);
• these electrodes can be used in the pH range of 2.0 - 5.0.

Electrodes' selectivity was good for tested interfering species (Na⁺, K⁺, and other alkaloids). The mentioned electrodes were used with good results for quantitative atropine sulphate assay by direct potentiometry from: 1‰ atropine sulphate injectable solution, Apitropin 1% eye drops, Chibro Atropine 1% eye drops and total alkaloids from extractum Belladonnae siccum expressed as hyoscine.

The mean recovery was between 97.8% and 100.1%, and the variation coefficient was between 0.35% and 0.82% (n=5).