Development of a Silver/Silver Ibuprofenate Potentiometric Sensor for Ibuprofen Quantification in Pharmaceutical Products

Nonsteroideal antiinflamatory drugs (NSAIDs) are the most used drugs  due to their analgesic, antipyretic and antiinflamatory properties, along with the fact that these are sold without the requirement of a medical prescription. Within this group of pharmaceutical compounds, ibuprofen (acid-α-methyl-4(isobutyl)-phenylacetic) is found. The use of Ibuprofen has increased because it is useful for treating headaches and arthritis. It is considered a safe drug since the human body can degrade it to its main metabolites and then excrete them through urine.

Nevertheless, to assure consumer’s health, it is necessary the development of analytical methodologies to allow an accurate and exact quantification of ibuprofen. Potentiometry has demonstrated to be an advantageous technique, where stands out the use of second type electrodes, which in accordance with the Nernst equation can detected  anions activities.

Considering this last, in this work we present the development and analytical characterization of a second-type electrode based on the Silver/Silver Ibuprofenate (Ag/AgIbu) pair.

A pure silver wire was modified using a 0.05 M sodium ibuprofenate solution and 0.1 M of sodium nitrate as supporting electrolyte. Chronoamperometry was used to achieve the modification of the electrode (Ag/AgIbu), the technique parameters were optimized and the registered optimums where: 0.8 V (vs Ag/AgCl) potential for 30 s. Calibration curves were performed to obtain the best analytical parameters: it was registered a sensitivity of -41.69 ± 1.61 mV/log (ibuprofenate molar activity), a linear range of 1.22x10^-4 - 8.98 x 10^-3 M, and a detection limit of 8.11x10^-5 M. Repeatability interpreted as the relative error percentage, was 2.46%. The pH effect on the system response was studied, it was found that the best working pH is 7.0. The electrode’s time response was 3.3 min with a drift of -0.01 mV s^-1. With the Matched Potential Method it was possible to determine that chloride and carbonate are the most important interferents.

Ibuprofen was measured in commercial drugs with no significant differences found between the manufacture’s reported value and the one obtained with the proposed sensor.