Complexes of tetra- tert-butyl-tetraazaporphine with Al(III) and Zr(IV) cations as fluoride selective ionophores (original) (raw)
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Electroanalysis, 2012
In this work, complexes of Zr(IV) and Al(III) cations with tert-butyl substituted tetraphenylporphyrin or tetraazaporphine were tested as F À -selective ionophores in plasticized aminated or carboxylated PVC membranes of ion-selective electrodes. It was found that functional groups present in the backbone of applied polymers influence the complexing properties of tested ligands, causing changes of F À -selectivity of electrodes prepared with their use in comparison with the electrodes with unmodified PVC membranes. This work shows, that application of functionalized PVC can eliminate the need of relatively expensive ionic sites addition to ion-selective membranes doped with metallocomplexes.
Zirconium(IV)-salophens as fluoride-selective ionophores in polymeric membrane electrodes
Analytica Chimica Acta, 2005
The feasibility of using Zr(IV)-salophens as ionophores to prepare anion-selective polymeric membrane electrodes is examined. It is shown that electrodes formulated with these compounds exhibit greatly enhanced selectivity towards fluoride anion (as compared to a classical quaternary ammonium anion-exchanger) when introduced into plasticized PVC films containing lipophilic anionic site additives. Electrodes constructed with optimal membrane compositions exhibit the following selectivity pattern:
Analytica Chimica Acta, 2006
Metallo-salens of cobalt(II) (Co-Sal), chromium(III) (Cr-Sal), and aluminum(III) (Al-Sal) are used as the active ionophores within plasticized poly(vinyl chloride) membranes. It is shown that central metal-ion plays a critical role in directing the ionophore selectivity. Polymer-membrane electrodes based on Co-Sal, Cr-Sal, and Al-Sal are demonstrated to exhibit enhanced responses and selectivity toward nitrite/thiocyanate, thiocyanate, and fluoride anions, respectively. The improved anion selectivity of the three ionophore systems is shown to deviate significantly from the classical Hofmeister pattern that is based only on ion lipophilicity. For example, optimized membrane electrodes for nitrite ion based on Co-Sal exhibit log K pot Nitrite,Anion values of −5.22, −4.66, −4.48, −2.5 towards bromide, perchlorate, nitrate, and iodide anions, respectively. Optimized membrane electrodes based on Co-Sal and Cr-Sal show near-Nernstian responses towards nitrite (−57.9 ± 0.9 mV/decade) and thiocyanate (−56.9 ± 0.8 mV/decade), respectively, with fast response and recovery times. In contrast, Al-Sal based membrane electrodes respond to fluoride ion in a super-Nernstian (−70 ± 3 mV/decade) and nearly an irreversible mode. The operative response mechanism of Co-Sal, Cr-Sal, and Al-Sal membrane electrodes is examined using the effect of added ionic sites on the potentiometric response characteristics. It is demonstrated that addition of lipophilic anionic sites to membrane electrodes based on the utilized metallo-salens enhances the selectivity towards the primary ion, while addition of cationic sites resulted in Hofmeister selectivity patterns suggesting that the operative response mechanism is of the charged carrier type. Electron spin resonance (ESR) data indicates that Co(II) metal-ion center of Co-Sal ionophore undergoes oxidation to Co(III). This process leads to formation of a charged anion-carrier that is consistent with the response behavior obtained for Co-Sal based membrane electrodes.
Aluminum(III) Porphyrins as Ionophores for Fluoride Selective Polymeric Membrane Electrodes
Electroanalysis, 2006
Aluminum(III) porphyrins are examined as potential fluoride selective ionophores in polymeric membrane type ionselective electrodes. Membranes formulated with Al(III) tetraphenyl (TPP) or octaethyl (OEP) porphyrins are shown to exhibit enhanced potentiometric selectivity for fluoride over more lipophilic anions, including perchlorate and thiocyanate. However, such membrane electrodes display undesirable super-Nernstian behavior, with concomitant slow response and recovery times. By employing a sterically hindered Al(III) picket fence porphyrin (PFP) complex as the membrane active species, fully reversible and Nernstian response toward fluoride is achieved. This finding suggests that the super-Nernstian behavior observed with the nonpicket fence metalloporphyrins is due to the formation of aggregate porphyrin species (likely dimers) within the membrane phase. The steric hindrance of the PFP ligand structure eliminates such chemistry, thus leading to theoretical response slopes toward fluoride. Addition of lipophilic anionic sites into the organic membranes enhances response and selectivity, indicating that the Al(III) porphyrin ionophores function as charged carrier type ionophores. Optimized membranes formulated with Al(III)-PFP in an o-nitrophenyloctyl ether plasticized PVC film exhibit fast response to fluoride down to 40 mM, with very high selectivity over SCN À , ClO 4 À , Cl À , Br À and NO 3 À (k pot < 10 À3 for all anions tested). With further refinements in the membrane chemistry, it is anticipated that Al(III) porphyrin-based membrane electrodes can exhibit potentiometric fluoride response and selectivity that approaches that of the classical solid-state LaF 3 crystal-based fluoride sensor.
Analytica Chimica Acta, 2007
Novel aluminum(III)-and zirconium(IV)-tetraphenylporhyrin (TPP) derivatives are examined as fluoride selective ionophores for preparing polymer membrane-based ion-selective electrodes (ISEs). The influence of t-butyl-or dichloro-phenyl ring substituents as well as the nature of the metal ion center (Al(III) vs. Zr(IV)) on the anion complexation constants of TPP derivative ionophores are reported. The anion binding stability constants of the ionophores are characterized by the so-called "sandwich membrane" method. All of the metalloporphyrins examined form their strongest anion complexes with fluoride. The influence of plasticizer as well as the type of lipophilic ionic site additive and their amounts in the sensing membrane are discussed. It is shown that membrane electrodes formulated with the metalloporphyrin derivatives and appropriate anionic or cationic additives exhibit enhanced potentiometric response toward fluoride over all other anions tested. Since selectivity toward fluoride is enhanced in the presence of both anionic and cationic additives, the metalloporphyrins can function as either charged or neutral carriers within the organic membrane phase. In contrast to previously reported fluoride-selective polymeric membrane electrodes based on metalloporphyrins, nernstian or near-nernstian (−51.2 to −60.1 mV decade −1 ) as well as rapid (t < 80s) and fully reversible potentiometric fluoride responses are observed. Moreover, use of aluminum (III)-t-butyltetraphenylporphyrin as the ionophore provides fluoride sensors with prolonged (7 months) functional life-time. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
Talanta, 2004
Poly(vinyl chloride) polymeric membranes plasticized with o-NPOE (o-nitrophenyl octyl ether) or DOS (dibutyl sebacate) and containing Zr(IV)-octaethyl(OEP)-or Zr(IV)-tetraphenylporphyrins (TPP) along with lipophilic cationic additives (tridodecylmethylammonium chloride; TDMACl) are examined potentiometrically and optically with respect to their response toward fluoride. It is shown that these zirconium porphyrins can function as neutral anion carriers within the organic membranes of the electrodes. Spectrophotometric measurements of thin polymeric films indicate that the presence of lipophilic cationic sites in the form of TDMA + and use of lower dielectric constant plasticizer (DOS) prevents formation of metalloporphyrin dimers in the organic polymer phase, which have been observed previously in polymeric membranes formulated with the same Zr(IV) porphyrins but with lipophilic anion site additives. By preventing dimer formation, rapid and Nernstian potentiometric response of the corresponding membrane electrodes toward fluoride ion is observed. Indeed, electrodes prepared with PVC/DOS membranes containing Zr(IV)-OEP and 15 mol% of TDMACl (relative to the ionophore) exhibit fast (t 95 < 15 s) and reversible response toward fluoride. The slope of calibration plots are near-Nernstian (−59.9 mV per decade). Such electrodes display the following selectivity pattern: ClO 4 − > SCN − > F − > NO 3 − > Br − > Cl − , which differs significantly from the classical Hofmeister series, with greatly enhanced potentiometric selectivity toward fluoride. The data presented herein, coupled with results from a previous study, confirm that Zr(IV) porphyrins can serve as either charged or neutral type anion carriers with respect to their enhanced interactions with fluoride when used as ionophores to prepare liquid-polymeric membrane electrodes, and that the nature of membrane additives and plasticizer dictates the response mechanism at play for given membrane formulations.
Analytical Sciences, 1998
With the evolution of ion-selective ionophore-based liquid/polymer membrane electrodes (ISEs) over the past 25 years, many cations of physiological and industrial significance can be measured effectively by direct potentiometry. However, there is a noticeable lack of analogous electrodes for many common anions. 1 Although commercial electrodes based on anionexchangers such as quaternary ammonium salts can be analytically useful, their selectivity patterns are always correlated solely with anion lipophilicity, resulting in the classical Hofmeister series (ClO 4->SCN-> salicyl a t e-> I-> N O 3-> B r-> N O 2-> C l-> H C O 3-> F-). 2 Therefore, highly hydrated anions such as fluoride, bicarbonate, chloride, and nitrite are difficult to monitor due to significant interference from more lipophilic anion species that may be present in the sample. Recently, examination of a variety of compounds that have strong yet reversible interactions with target anions has resulted in new ionophores with decidedly non-Hofmeister selectivity toward anions. 3,4 Many research groups are studying a wide variety of new ionophores that demonstrate these characteristics such as mercury 5 , silver 6 , and tin 7 organometallic compounds, fluorinated (poly)ethers 8 , metallophthalocyanines 9 , metallocenes 10 , and trifluoroacetyl derivatives. 11 The pioneering work of Simon et al., in which the behavior of lipophilic vitamin B 12 derivatives as ionophores was examined, led to one of the first nitrite 79
Analytica Chimica Acta, 2002
A series of bis(halodiphenylstannyl)alkanes (Ph 2 XSn) 2 (CH 2 ) n , (X: Cl, Br, OAc, n = 1-4) have been evaluated as fluoride ionophores in polymeric-membrane ion-selective electrodes. It is shown that the selectivity pattern of these molecules is governed by their structural characteristics. An entirely non-Hofmeister selectivity sequence with a remarkable preference towards fluoride is obtained for bis(chlorodiphenylstannyl)methane, (Ph 2 ClSn) 2 CH 2 . The latter compound was utilised for further studies on the improvement of the ISEs selectivity towards fluoride. The optimum membrane composition for best potentiometric performance was achieved with DOS-elasticised membranes doped with 10 mol% KTpClPB, suggesting that this compound operates via a charged-carrier mechanism. This membrane composition results in a preference to fluoride over several lipophilic anions, such as perchlorate, nitrate and iodide.