Dual analytical approach for niflumic acid: HPLC determination and electrochemical sensing by quaternary ammonium salt-assisted modification of pencil graphite electrode

Abstract

In this study, a novel and efficient electrochemical sensing platform for the determination of niflumic acid (NFA) was developed based on a quaternary ammonium salt-assisted modification of a pencil graphite electrode (PGE) in a non-aqueous medium. The electrode surface was electrochemically polarized using tetrabutylammonium hexafluorophosphate (TBAPFs) dissolved in dimethyl sulfoxide (DMSO), leading to the formation of a positively charged and ionically organized interface. Systematic optimization studies revealed that the optimal electrode fabrication conditions were obtained using 0.025 M TBAPFs in DMSO, two cyclic voltammetric cycles, and a synthesis potential window of -0.2 to -2.75 V. Electrochemical impedance spectroscopy (EIS) demonstrated a pronounced decrease in charge-transfer resistance from 128.54 Omega for the bare PGE to 82.08 Omega for the TBAPFs/ DMSO/PGE, confirming significantly enhanced interfacial electron-transfer kinetics. The modified electrode exhibited excellent electroanalytical performance toward niflumic acid in Britton-Robinson buffer (pH 5.0), providing a low detection limit of 1.61 & times; 10-7 M (161 nM), a quantification limit of 5.38 & times; 10-7 M, and good repeatability with an RSD of 3.49%. The sensor showed high selectivity in the presence of common interfering species and was successfully applied to real pharmaceutical samples, yielding recoveries between 100.59% and 104.75%. Furthermore, ferri/ferrocyanide probe studies confirmed that the enhanced electrochemical response originates from intrinsic improvements in interfacial conductivity rather than analyte-specific effects. Complementary spectroscopic and morphological characterizations (SEM, FT-IR, and XRD) further support the successful surface modification of the electrode. The proposed TBAPFs/DMSO/PGE platform offers a simple, cost-effective, and reliable alternative for sensitive niflumic acid determination in pharmaceutical analysis.