New Insights on Naproxen Quantification Using Voltammetry and Graphite Electrodes: Development of an Optimized and Competitive Methodology

The non-steroidal anti-inflammatory drugs (NSAID’s) comprise a group of compounds bearing different chemical structures, displaying primarily an inhibition capacity of the prostaglandins synthesis through inhibition of the enzyme cyclo-oxygenase [1]. These medicaments share similarly undesirable pharmacological actions and effects. Naproxen is found among the group of widely prescribed and well-known pharmaceuticals, Figure 1, which exhibit anti-inflammatory analgesic and anti-pyretic properties [2]. The fact that naproxen is much more commonly used with and without appropriate medical prescription has made it necessary to implement stricter quality controls for this drug; during the last years it has also been considered an emerging contaminant in residual waters systems.

Figure 1. Naproxen’s chemical structure

Naproxen, acid ((S)-2-(6-methoxy-2-naftyl) propanoic acid) is a non-steroidal anti-inflammatory drug, frequently used to diminish pain, fever, inflammation and the stiffness provoked through osteoarthritis, rheumatoid arthritis, and other illnesses [3]. Naproxen is considered an NSAID of the propionic acid group with a pKa of 4.2, it is liposoluble, practically insoluble in water at pH < 4, though when the pH > 6, the reverse is true [1].

The present work discuses new findings in the electrochemistry of naproxen over graphite electrodes. This new approach, along with a formal optimization of the variables related with differential pulse voltammetry, allows the proposal of a simple and competitive low-cost method to carry out naproxen’s voltammetric quantification. Naproxen’s indirect quantification through an adsorption anodic wave was performed at a graphite bar electrode using differential pulse voltammetry. An anodic current maximum was recorded at a potential of -0.3 V referred to a saturated Ag/AgCl reference electrode, in the presence of 0.1 mol dm^-3 phosphates buffer at pH 7. A calibration plot was done, having a correlation coefficient of 0.990, with a sensibility of 4.19 ± 0.62  µA cm³ µg^-1, with detection and quantification limits of 0.68 and 3.3 µg cm^-3, respectively, and a quantification interval of 3.3 - 28.18 µg cm^-3. The method proposed was adequate for naproxen quantification in pharmaceutical samples.

 References

 [1] P. Todd, S. Clissold, Naproxen. A reappraisal of its pharmacology, and therapeutic use in rheumatic diseases and pain states, Drugs 40 (1) (1990) 91-137.

[2] B. Raskin,  Gastrointestinal effects of nonsteroidal anti-inflammatory, Therapy  Americ. J. Medic. 106 (1999) 3S–12S.

[3] C. Boynton, C. Dick, G. Mayer, NSAIDs: An Overview, J. Clin. Pharmacol. (28) 6 (1998) 512-517.