Abstract
Levofloxacin (LF) is a medically important antibiotic drug that is used to treat a variety of bacterial infections. In this study, three highly sensitive and selective carbon paste electrodes (CPEs) were fabricated for potentiometric determination of the LF drug: (i) CPEs filled with carbon paste (referred to as CPE); (ii) CPE coated (drop-casted) with ion-selective PVC membrane (referred to as C-CPE); (iii) CPE filled with carbon paste modified with a plasticizer (PVC/cyclohexanone) (referenced as P-CPE). The CPE was formulated from graphite (Gr, 44.0%) and reduced graphene oxide (rGO, 3.0%) as the carbon source, tricresyl phosphate (TCP, 47.0%) as the plasticizer; sodium tetrakis[3,5-bis(trifluoromethyl)phenyl] borate (St-TFPMB, 1.0%) as the ion exchanger; and levofloxacinium-tetraphenylborate (LF-TPB, 5.0%) as the lipophilic ion pair. It showed a sub-Nernstian slope of 49.3 mV decade−1 within the LF concentration range 1.0 × 10−2 M to 1.0 × 10−5 M, with a detection limit of 1.0 × 10−5 M. The PVC coated electrode (C-CPE) showed improved sensitivity (in terms of slope, equal to 50.2 mV decade−1) compared to CPEs. After the incorporation of PVC paste on the modified CPE (P-CPE), the sensitivity increased at 53.5 mV decade−1, indicating such improvement. The selectivity coefficient () against different interfering species (Na+, K+, NH4+, Ca2+, Al3+, Fe3+, Glycine, Glucose, Maltose, Lactose) were significantly improved by one to three orders of magnitudes in the case of C-CPE and P-CPE, compared to CPEs. The modification with the PVC membrane coating significantly improved the response time and solubility of the LF-TPB within the electrode matrix and increased the lifetime. The constructed sensors were successfully applied for LF determination in pharmaceutical preparation (Levoxin® 500 mg), spiked urine, and serum samples with high accuracy and precision.
Highlights
polyvinyl chloride (PVC) membrane electrodes (PVCEs) are one of the subdivisions of potentiometric sensors
IP: ion-pair (LF-TPB); PVCM: PVC contents used in the formulation of PVC membrane of the PVCEs; Gr: Graphite; StTFPMB: sodium tetrakisphenyl borate as an ion exchanger; CD: cyclodextrin as a modifier; multiwalled carbon nanotubes (MWCNTs); multi-walled carbon nanotubes as carbon modifier; rGO: reduced graphene oxide as carbon modifier; TCP: tricresyl phosphate as a plasticizer, PVCP: PVC liquid paste used in the preparation of the P-carbon paste electrodes (CPEs); DOP: dioctyl phthalate as a plasticizer, LOD: limit of detection in M; slope in mV/conc.decade; Relative standard deviation (RSD): relative standard deviation for three measSensors 2021, 21, 3150 urements; *Coated: PVC membrane of composition in sensor 4 coated on the CPE
IP: ion-pair (LF-TPB); PVCM: PVC contents used in the formulation of PVC membrane of the PVCEs; Gr: Graphite; St-TFPMB: sodium tetrakisphenyl borate as an ion exchanger; CD: cyclodextrin as a modifier; MWCNTs; multi-walled carbon nanotubes as carbon modifier; rGO: reduced graphene oxide as carbon modifier; TCP: tricresyl phosphate as a plasticizer, PVCP: PVC liquid paste used in the preparation of the paste on the modified CPE (P-CPE); DOP: dioctyl phthalate as a plasticizer, LOD: limit of detection in M; slope in mV/conc.decade; RSD: relative standard deviation for three measurements; *Coated: PVC membrane of composition in sensor 4 coated on the CPE
Summary
PVC membrane electrodes (PVCEs) are one of the subdivisions of potentiometric sensors. Electrode (ISEs) that have attracted great attention due to their chemical inertness, robustness, renewability, stable response, low ohmic resistance, no need for an internal solution, offering an renewable surface for electron exchange, and suitability for a variety of sensing and detection applications [2,3] These electrodes are typically made of graphite powder, ionophore for binding the analyte, pasting liquid (mineral oils), and other modifiers that facilitate the mobility and binding of the analytical species in the sample solutions with the electrode active surface, which in turn reduces the response time [4,5]. The carbon paste of CPEs has been modified by ionic liquid, tetraphenyl borate derivatives and conductive polymers, which is not possible in the case of PVCEs [2,3,6] These modifications significantly improved the detection limit of the CPEs, intrinsic conductivity, the solvating ability for a wide range of soluble and insoluble ionophores, and linear dynamic range, response time, and other properties [6,7].
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