Response Characteristics of Anion-Selective Polymer Membrane Electrodes Based on Gallium(III), Indium(III) and Thallium(III) Porphyrins

Abstract

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 eTherefore, 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 selective liquid/polymer membrane electrodes. 12 Metalloporphyrins, which are one carbon larger but structurally analogous to the cobyrinate ring of vitamin B 12 , also exhibit unique anion ionophore properties when incorporated into plasticized polymer membranes. Mn(III) [13][14][15][16][17][18][19][20] , Co(III) 13,16,[21][22][23][24][25][26] , Ru(II) 16 , and Sn(IV) 25,27-29 porphyrin-based ISEs have been shown to exhibit useful selectivity for thiocyanate, nitrite/thiocyanate, thiocyanate, and salicylate, respectively. More recently, the nature of the ionophore-anion interaction mechanism has been correlated to the charge of the central metal ion.25 Metal(II) porphyrins were found to serve as neutral carriers, metal(IV) as charged carriers and metal(III) porphyrins as either neutral or charged depending on the existance and number of bound axial ligands. The use of lipophilic ionic additives, either cationic (quaternary ammonium salts for neutral carriers) or anionic (tetraphenylborate salts for charged carriers) can help to determine the dominant mechanism within the polymer membrane responsible for EMF response. 30 These ionic sites have also been found to improve general electrode performance by reducing the membrane resistance, decreasing counter-ion interference, and enhancing selectivity. 25,[30][31][32] In this work, porphyrins containing group XIII ions as metal centers are examined as unique ionophores in the preparation of anion ISEs. Electrodes based on indium(III) porphyrins in poly(vinyl chloride) (PVC) membranes have been shown previously to exhibit enhanced responses toward...

Polymeric membrane electrodes with improved fluoride selectivity and lifetime based on Zr(IV)- and Al(III)-tetraphenylporphyrin derivatives

“…Similarly, thus far, relatively few useful fluoride-selective polymeric membrane electrodes have been reported [8][9][10][11][12][13][14][15]. Most suffer from practical problems such as high level of interference by lipophilic anions [11,12,15], super-nernstian response slopes, sluggish and not fully reversible response properties [8,9,10,14] and short use lifetimes of the electrodes [14].…”

“…Most suffer from practical problems such as high level of interference by lipophilic anions [11,12,15], super-nernstian response slopes, sluggish and not fully reversible response properties [8,9,10,14] and short use lifetimes of the electrodes [14]. Recent research has suggested that membranes formulated with Al(III) octaethylporhyrin (Al [OEP]) and Al(III) tetraphenylporphyrin (Al[TPP]) [14] exhibit very high potentiometric selectivity towards fluoride anions, and this has led also to the design of highly selective optical fluoride sensors with sub-micromolar fluoride ion detection limit [16,17].…”

Fluoride-Selective Optical Sensor Based on Aluminum(III)−Octaethylporphyrin in Thin Polymeric Film: Further Characterization and Practical Application

“…19 Recently it was found that polymer membranes doped with Ga(III) and Zr(IV) porphyrins exhibit an enhanced potentiometric selectivity for fluoride due to the ability of these species to interact selectively with fluoride ion via a preferred axial ligation reaction. [20][21][22][23][24] Further, it appears that the Ga(III) and Zr(IV) porphyrins may be useful for preparing bulk-optode sensing films for fluoride without the need for addition of a suitable pH indicator, owing to the ability of fluoride ion binding to the respective metal ion centers to alter the equilibrium between monomeric porphyrins and hydroxide ion bridged dimeric porphyrins within the polymeric film. 20-23 The dimer and monomeric species have different Soret band λ max for absorption.…”

Sulfadiazine-selective determination in aquaculture environment: Selective potentiometric transduction by neutral or charged ionophores

“…PPHR complexes with transition metal ions are very stable and are often used to construct structures in supramolecular chemistry, taking advantage of the Lewis acidity of the coordinated metal [16]. Several metalloporphyrins have been employed as electroactive components in the membrane of potentiometric sensors, and their response to anions has been interpreted by a dissociation ion-exchange mechanism or metal-ligand interaction mechanism [16][17][18][19][20].…”