Highly selective and sensitive potentiometric determination of favipiravir in COVID-19 antiviral drug formulations

In this study, a novel all-solid-state electrochemical sensor based on favipiravir-tetraphenylborate (FAV-TPB) electroactive material was developed and reported for FAV's highly selective and sensitive potentiometric determination in COVID-19 antiviral drug formulations. All-solid-state FAV selective sensor was fabricated by mixing and properly pressing FAV-TPB, graphite (G), multi-walled carbon nanotube (MWCNT), and paraffin oil (PO). In order to obtain the best sensor response, the sensor component ratios were optimized. The most satisfying response characteristics was obtained with the sensor composition FAV-TPB:G:MWCNT:PO in the ratio 32.5:42.5:5:20 (w/w %). The developed sensor displayed a wide linear near-Nernstian response to FAV over the concentration of 1.0 x 10-6 - 1.0 x 10- 1 molL- 1 with a slope of 53.6 +/- 1.4 mV (R2 = 0.9997). The detection limits of the sensor was calculated as 6.0 x 10- 7molL- 1, respectively. The dynamic response time of the sensor was 7 s, and the sensor exhibited fairly reproducible potentiometric responses. In the pH range of 6.0-8.0, the sensor's potential response was not affected by the pH change of the test solutions. The improved sensor had a wide temperature tolerance, and its response remained unchanged in the 10-40 degree celsius temperature range. The interference effect of some chemical and biological species was evaluated by the matched potential method and separate solution method. The sensor worked stable for 12 weeks without any considerable change in its potential response. The analytical applications of the sensor were successfully carried out with the potentiometric titration of FAV with sodium tetraphenylborate solution and also the direct determination of favipiravir in COVID-19 antiviral drug formulations.