Improving the detection limit of anion-selective electrodes: An iodide-selective membrane with a nanomolar detection limit
ABSTRACT The lower detection limit and the selectivity behavior of anion-selective electrodes (ISEs) are improved by using optimized inner solutions and membrane compositions. With a membrane based on the recently described ionophore mercuracarborand-3, a detection limit of 2 x 10(-9) M has been achieved for iodide. Nevertheless, the improvements are less pronounced than in the case of cation ISEs. This is mainly due to the fact that so far no anion ISE is known with the extremely high selectivities of cation ISEs. If the membrane does not contain an ionophore, leaching of the ion exchanger from the membrane into the sample is also a relevant limiting factor except for ion exchangers of very high lipophilicity.
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- "Recently, electrodes based on derivatives of vitamin B 12 or on transition metal complexes of porphyrin, phthalocyanine, metallocenes, and Schiff base (Schulthess et al. 1985; Stepanek at al. 1986; Chaniotakis et al. 1988; Daunert and Bachas 1989; Huser et al. 1990; Daunert et al. 1991; Rothmaier and Simon 1993; Gao et al. 1994; Yuan et al. 1993; Shamsipur et al. 2003; Ganjali et al. 2003) have been reported as typical examples of nonconventional carriers with potential response characteristics apparently deviating from the Hofmeister sequence. Due to the outstanding work of the groups of Pretsch, Bakker, Bühlmann, and Meyerhoff, who reported many important theoretical and experimental works with the crucial achievement of improving the low detection limit near nanomolar concentrations, the field of ion-selective electrodes has expanded, especially in the last decades (Bakker et al. 1997; Mi et al. 1999; Malon et al. 2003; Radu et al. 2003). In view of the gradually understood importance of a lipophilic ionic additive (so-called ionic sites) in membrane cocktails, to potentiometric responses of membrane electrodes, the direct incorporation of lipophilic ionic additives into polymer membranes has become a fairly standard practice for anion-selective electrodes, in order to improve the selectivity of the studied electrodes towards the target anion and the response slopes, as well as to provide information of possible response mechanism of the chosen ionophore (Bakker et al. 1994; Steinle et al. 1998; Steinle et al. 2000; Schaller et al. 1994). "
ABSTRACT: Three kinds of transition metal chelates of unsymmetrical tetradentate Schiff base, o‐hydroxybenzophenone‐1,2‐diaminobenzene‐pyrrole‐2‐carbaldehyde(H2L), were synthesized to prepare anion‐selective electrodes and their anion response characteristics were investigated. The results show that the performances of the electrodes are considerably influenced by the nature of the central metals. The proposed electrode with the Cu(II)‐chelate and cationic additive demonstrated an anti‐Hofmeister selectivity sequence with a good selectivity towards thiocyanate in the following order: Thiocyanate>iodide>salicylate>perchlorate>bromide>nitrite>chloride>acetate>fluoride>nitrate>sulfite>sulfate. The electrode had an excellent linear response to thiocyanate from 3.4×10 to 1.0×10 M in phosphate buffer solution at pH 5.0 with a slope of −58.7 mV per decade, a detection limit of 1.6×10 M, and a fast response time within 5 s over the entire concentration series. Spectroscopic techniques and AC impedance were used to investigate the response mechanism to thiocyanate of the membrane doped with Cu(II)‐chelate. The preliminary application of the electrode for determination of thiocyanate in wastewater and urine samples is reported.Analytical Letters 01/2007; 40(2):369-386. DOI:10.1080/00032710600964742 · 0.98 Impact Factor
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ABSTRACT: A triiodide-selective electrode based on copper (II)-Schiff base complex as a membrane carrier is proposed. The electrode was prepared by incorporating the carrier into a plasticized polyvinylchloride (PVC) membrane and was directly coated on the surface of a graphite electrode. The obtained electrode showed a near Nernstian slope of 57.0 ± 0.4 mV/decade to I 3 − ions over an activity range of 1.0 × 10−5−1.0 × 10−1 M with a limit of detection of 4.8 × 10−6 M. The response time of the electrode was fast (5 s) and the electrode could be used for about 2 months without considerable divergence in response. The potentiometric selectivity coefficients were evaluated and displayed anti-Hofmeister behavior. The electrode was used as an indicator electrode in the potentiometric titration of the triiodide ion and in the determination of ascorbic acid in vitamin C tablets.Journal of Analytical Chemistry 07/2006; 61(7):677-682. DOI:10.1134/S1061934806070136 · 0.81 Impact Factor
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ABSTRACT: Three platinum(II) complexes were synthesized and studied to characterize their ability as an anion carrier in a PVC membrane electrode. The polymeric membrane electrodes (PME) and also coated glassy carbon electrodes (CGCE) prepared with one of these complexes showed excellent response characteristics to perchlorate ions. The electrodes exhibited Nernstian responses to ClO4 − ions over a wide concentration range from 1.5 × 10−6 to 2.7 × 10−1 M for PME and 5.0 × 10−7 to 1.9 × 10−1 M for CGCE with low detection limits (9.0 × 10−7 M for PME and 4.0 × 10−7 M for CGCE). The electrodes possess fast response time, satisfactory reproducibility, appropriate lifetime and, most importantly, good selectivity toward ClO4 − relative to a variety of other common anions. The potentiometric response of the electrodes is independent of the pH of the test solution in the pH range 2.0–9.0. The proposed sensors were used in potentiometric determination of perchlorate ions in mineral water and urine samples.Monatshefte fuer Chemie/Chemical Monthly 12/2008; 139(12):1439-1445. DOI:10.1007/s00706-008-0947-8 · 1.35 Impact Factor