Elsevier

Analytica Chimica Acta

Volume 404, Issue 1, 10 January 2000, Pages 111-119
Analytica Chimica Acta

All-solid-state calcium-selective electrode prepared of soluble electrically conducting polyaniline and di(2-ethylhexyl)phosphate with tetraoctylammonium chloride as cationic additive

https://doi.org/10.1016/S0003-2670(99)00686-8Get rights and content

Abstract

A novel all-solid-state Ca2+-selective electrode was prepared of soluble electrically conducting polyaniline (PANI), di(2-ethylhexyl)phosphate (H+DEHP) and tetraoctyl ammonium chloride (TOA+Cl). PANI is made soluble and electrically conducting in tetrahydrofuran (THF) with H+DEHP. The DEHP anion is a complexing agent of the charged carrier type for Ca2+. TOA+Cl is added to this solution and electrode membranes are then prepared by drop casting on a GC substrate. PANI membranes containing 0–40% (m/m) TOA+Cl has been studied in this work.

The Ca2+-sensitivity was significantly improved by incorporation of 20–30% (m/m) TOA+Cl in the PANI electrode membrane. The best Ca2+-sensitivity, 27.0 ± 0.4 mV/log aCa (10−1–10−3 M CaCl2, n = 3, LOD = 10−4 M) in 0.1 M NaCl, was obtained with an electrode membrane containing 25% TOA+Cl (PANI25). The reproducibility of the standard potential of three identical PANI25 electrodes was also very good. The selectivity coefficient (logKCa,jpot) of this electrode towards j = Na+, K+ and Li+ is −1.6. However, Mg2+ shows severe interference in determination of Ca2+.

No redox sensitivity was observed for the PANI25 electrode in a 10 mM Fe(CN)63−/4− solution with 0.1 M CaCl2 as the ionic background and only a weak redox response, 5 mV/decade, could be detected with 10−3 M CaCl2 as the ionic background. The pH sensitivity of the PANI25 electrodes studied was found to be approximately 5 mV/pH within the pH range of 4.5–9.7.

Furthermore, the impedance spectrum and the cyclic voltammogram of the PANI25 electrode reveal that TOA+Cl improves the ionic mobility within the PANI membrane. Finally, it is shown that the working mechanism of the PANI electrode membrane can be explained with the charge carrier model, which is usually applied to PVC-based ion-selective electrodes.

Introduction

This paper presents a further development of the all-solid-state calcium electrode that is described in a previous paper [1]. Schaller et al. [2] have reported that incorporation of ionic sites into a PVC-based ion-selective membrane (ISM) improves the potentiometric performance of a charged carrier-based ion-selective electrode (ISE) of the conventional type with an inner reference solution. They showed that anion exchangers are needed for cation-selective electrodes and vice versa. In their experiments, incorporation of the anion exchanger tridodecylammonium chloride (TDMA+Cl) creates positively charged cationic sites (TDMA+) in the ISM. This improved the selectivity, the slope of the calibration curve, the long-term stability and lowered the electrode resistance of a calcium-selective electrode with dinonylnaphthalenesulfonic acid (DNNS) as the charged carrier for Ca2+. The reason for the improved performance was that the concentration of the uncomplexed negatively charged carrier increased, in order to fulfill the electroneutrality condition in the ISM, as the concentration of TDMA+ increases in the membrane. The concentration of the uncomplexed negatively charged carrier in the ISM can therefore, be kept constant and thus the concentration of uncomplexed Ca2+ ions and interfering ions in the membrane decreases. Finally, the ionic strength in the electrode membrane will mainly be determined by TDMA+ and the negatively charged carrier and is therefore, not influenced by the ionic strength of the sample solution.

In this work we will study if the concept presented by Schaller et al. [2] can also be applied to an electrically conducting PANI-based ISE membrane free of PVC. Tetraoctylammonium chloride (TOA+Cl) will be incorporated in an all-solid-state PANI electrode membrane to improve the Ca2+-sensitivity. The PANI membrane contains also DEHP which is a negatively charged carrier for Ca2+. Electrode membranes containing 0–40% (m/m) TOA+Cl will be studied.

Section snippets

Reagents

Tetraoctylammonium chloride (TOA+Cl) was obtained from Aldrich. All the other chemicals used in this work have been described in previous paper [1]. The chemical structures of the membrane components used in this work are shown in Fig. 1.

Protonation of polyaniline and electrode preparation

Protonation of polyaniline and electrode preparation were done according to the same procedure as described in a previous paper [1]. The following electrode membrane compositions were studied: 60–100% (m/m) PANI (which also includes H+DEHP) and 0–40% (m/m) TOA

Ca2+-sensitivity

H+DEHP is used to protonate the emeraldine base (EB) form of polyaniline in order to transform the non-conducting EB form to the conducting emeraldine salt (ES) form of polyaniline. H+DEHP molecules form strong hydrogen bonds between themselves. Those H+DEHP molecules that protonate PANI and make it soluble, can therefore, be solvated by the free H+DEHP molecules present in the protonation solution. H+DEHP is therefore, enriched in the soluble fraction (ES form) of PANI. The molar ratio (y

Conclusions

A novel all-solid-state Ca2+-selective electrode based on electrically conducting polyaniline, di(2-ethylhexyl)phosphate and tetraoctylammonium chloride is presented in this paper. The working mechanism of the electrode membranes containing 20–30% tetraoctylammonium chloride can be explained with the charged carrier model that is usually applied to ion-selective electrodes based on plasticized PVC membranes. The number of components required for the membrane preparation can be reduced with this

References (9)

  • A. Pron et al.

    Synth. Met.

    (1993)
  • A. Cadogan et al.

    Talanta

    (1992)
  • J. Bobacka et al.

    Talanta

    (1993)
  • J. Bobacka et al.

    Anal. Chim. Acta

    (1999)
There are more references available in the full text version of this article.

Cited by (65)

  • Improving the stability of Pb<sup>2+</sup> ion-selective electrodes by using 3D polyaniline nanowire arrays as the inner solid-contact transducer

    2021, Electrochimica Acta
    Citation Excerpt :

    In order to improve the potential stability and reproducibility of all-solid-state ISEs, various conductive materials including conducting polymers (including polyaniline, polypyrrole and poly(3,4-ethylenedioxythiophene)) [7,8], carbon-based nanomaterials [9,10] and metal-based nanomaterials [11,12] have been investigated as solid contact (SC) materials. In addition, further efforts have been made to improve electrode stability by enhancing the capacitance [13,14] or hydrophobicity [15,16] of the transducer materials. Various strategies have been used to modify the capacitance performance [17–19], with improving the specific surface area (SSA) [20,21] recognized as one of the most effective approaches.

  • A novel all-solid-state ammonium electrode with polyaniline and copolymer of aniline/2,5-dimethoxyaniline as transducers

    2015, Journal of Electroanalytical Chemistry
    Citation Excerpt :

    On the other hand, since the first successful preparation of the coated wire electrodes in 1971, by Cattrall and Freiser [13], the all-solid-state ion-selective electrodes have gone through four stages, namely coated wire electrodes [13], neutral ionophore electrodes [14], hydrogel electrodes [15] and conductive polymer electrodes [16]. Electrochemical materials have achieved great progress in recent years, high performance solid ionic conductor has been used to make batteries, and electrodes [17–21], such as poly(3,4-ethylenedioxythiophene) for Ca2+ and Pb2+ [22,23], polypyrrole for urea [24], and polyaniline for Ca2+ [25]. Subsequently, the conductivity, chemical activity and catalytic activity of inorganic membrane materials have been improved by ion doping technology [26,27], and the organic and inorganic composite membranes have been used for fabricating electrodes [28].

  • Advanced solid-contact ion selective electrode based on electrically conducting polymers

    2012, Fenxi Huaxue/ Chinese Journal of Analytical Chemistry
View all citing articles on Scopus
View full text