Dopamine Ion-Selective Electrode for Potentiometry in Pharmaceutical Preparations

 This paper reports the construction and evaluation of a dopamine sensitive electrode and its usefulness for the determination of this compound by direct potentiometry in pharmaceutical preparations. The electrode comprised a carboxylated poly(vinyl chloride) membrane based on β-cyclodextrine dissolved in 2-fluoro-2-nitrodiphenyl ether and using tetrakis(p-chlorophenyl) borate as a fixed anionic site. For comparison purposes membranes with similar composition but including normal high molecular weight PVC were also prepared. The electrodes including carboxylated poly(vinyl chloride) presented linear response within the concentration range of 5×10⁻⁵ and 10⁻¹ mol dm⁻³ of dopamine with a slope of about 59 mV decade⁻¹ of activity, in the pH range of 2 to 7.5 units. The response time was less than 15 seconds. Selectivity coefficients for different interferents including sodium, potassium, ammonium, lithium, epinephrine and norepinephrine were evaluated using the separated solution method and no significant interferences were observed. The electrode displays useful analytical characteristics for the direct determination of dopamine in pharmaceutical preparations. Results with an average recovery of 98.6±0.3% were obtained. Received May 28, 1998. Revision March 2, 1999.