Properties of ion-selective electrodes with polymer membranes for ibuprofen determination

Composition of a polymeric potential-determining phase for the ibuprofen selective electrode was determined. The different possibilities of using various quaternary ammonium salts — dimethyldidecylammonium bromide, methyltrioctylammonium chloride, tetraoctylammonium chloride and methyltrioctyloammonium 2-(4-isobuthylphenyl) priopionate — as anion exchangers in polymer membranes of ibuprofen electrodes were examined. The following basic electrode parameters were investigated: measurement range, slope, limit of detection, lifetime, dependence of the electrode potential on pH and selectivity coefficients in relation to some organic and inorganic anions.

Experimental comparison of several quaternary ammonium salts used as electroactive materials in ibuprofen electrodes shows that the methyltrioctylammonium chloride PVC membrane sensor plasticized with mixed plasticizers 5% TBP and 95% DIBP possesses the best performance characteristics. The electrode shows a near-Nernstian characteristics slope of 60 mV decade!1 in ibuprofen concentration in the range of 10!4–10!1mole L!1 and low limit of detection 4 10!5 mole L!1. The electrode exhibits the selectivity coefficients against some organic and inorganic ions determined by the SSM and MPM methods in the ! ! sequence: NO3 >benzoate>acetate>Br!>H2PO4 > ! Cl >sulfate > citrate. The interfering agents were chosen to check if selectivity were correct for the type of membranes in which the ability of ion penetration from the aqueous phase to the organic phase depends only on the hydration energy of a given anion. The selectivities follow the Hofmeister series. If would be of significant importance also to study the extent of other interfering agent actions, e.g., those constituting the tablet mass. However, auxiliary substances such as gelatin, cellulose acetate, lactose, poly-ethylene glycol, magnesium stearate, sodium lauryl sulfate or injection solvents do not disturb the potentiometric measurements [10]. The ibuprofen electrode can be used for determination of the (2-(4-isobuthylphenyl)propionate) anion in pharmaceutical preparations, for testing drug qualities and in the process of their production in the aqueous solutions of ibuprofen concentrations over 4 10!5 mole L!1 due to the short electrode response time (20 s), sufficient measurement range (4 10!5–10!1 mole L!1) and long electrode lifetime (3 months) stored at +4°C.