Potentiometric screen-printed sensor for determination of oxybutynin hydrochloride
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ORIGINAL PAPER
Potentiometric screen‑printed sensor for determination of oxybutynin hydrochloride Rehab O. El‑Attar1 · Hassan A. M. Hendawy2 · Elmorsy Khaled1 Received: 9 January 2020 / Accepted: 9 June 2020 © Iranian Chemical Society 2020
Abstract The present work describes the fabrication of disposable screen-printed oxybutynin hydrochloride (OXB) potentiometric sensors. The electrode matrix composition was investigated on the basis of the effect of the nature and concentration of sensing ionophores, anionic sites, plasticizers and nanomaterials. Incorporation of single-walled carbon nanotubes (SWCNTs) as transducer and (2, 3, 6-tri-O-methyl)-β-cyclodextrin as molecular recognition elements in the electrode matrix improved both the sensitivity and selectivity of the sensor towards oxybutynin hydrochloride. The fabricated sensors showed Nernstian slope of 57.5 ± 1.0 mV decade−1 in the concentration range from 1 0–6 to 1 0–2 mol L−1 OXB with detection limit of 8 × 10–7 mol L−1. Moreover, the presence of SWCNTs in the electrode matrix enhanced the potential reading stability, response time ( heptakis(2,6-tri-O-methyl)β-CD > native β-CD. All the studied β-CD derivatives have the same cavity diameter and the variation in the stability constants may be explained on the basis of the increasing cavity height and lipophilicity generation by substitution with methyl derivatives. However, the unsubstituted β-CD has a height of 8 Å, therefore part of the drug could still be outside the nanocage (vide infra). In addition, the presence of the methyl groups increased the height of ring cavity to 11 Å which enhanced more penetration and fitting of the drug inside the ring cavity [42]. Effect of ionic sites Neutral ionophore-based potentiometric sensors operate only when ionic sites with opposite charge to the target analyte are present in the sensing membrane matrix [43–45]. In addition, the presence of lipophilic ionic sites promotes the
interfacial ion-exchange kinetics at the sensing membrane surface and diminishes the membrane resistance which enhances both the selectivity and sensitivity of the sensor. Blank electrode matrix fabricated without ionic sites showed Nernstian response about 36.4 ± 0.35 mV decade−1 (Fig. 3a), while those incorporated with different ionic sites showed higher Nernstian response (52.6 ± 1.3, 58 ± 1.0 and 56.8 ± 0.7 mV decade−1 for NaTPB, KTClPB and NaTFPB, respectively). Performing potentiometric titration of OXB against NaTPB applying sensors contained different ionic sites (Fig. 3b) showed the superiority of potassium tetrakis (KTClPB) indicated by high potential jump and potential change at the inflexion point. Effect of membrane plasticizers The dielectric constant of plasticizers governs the polarity of sensing membrane, control the molecular recognition element and the stability of the formed inclusion complex [46, 47]. In the present study, five different plasticizers with different dielectric constants were applied as membrane mediator, namely, DOP, DOS, TCP, o-NPOE and f-PNPE (ɛ
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