Optical Chloride Sensor Based on Dimer−Monomer Equilibrium of Indium(III) Octaethylporphyrin in Polymeric Film

Abstract

A novel transduction chemistry for preparing optical anion-selective polymeric films that respond reversibly and selectively to chloride ion activity is demonstrated. The chloride sensors are prepared by casting thin (5-10 microm) plasticized PVC films containing indium(III) octaethylporphyrin hydroxide, along with optimized levels of a lipophilic tetraphenylborate salt, onto glass slides. When bathed in low-pH buffered solutions void of chloride, the porphyrin species spontaneously forms a hydroxide ion-bridged dimer, with the added lipophilic borate species serving as the counteranion for this complex. The maximum for the Soret absorption band of this dimeric species is shifted to 390 nm, from 410 nm for the initial monomeric porphyrin. Increases in chloride ion levels in the bathing solution results in chloride extraction and ligation to the In(III) center, and concomitant breaking of the dimer into monomeric porphyrin species, yielding a decrease in absorbance at 390 nm and an increase in optical signal at 410 nm. Under optimized conditions, optical selectivity coefficients toward chloride over a wide range of other anions (NO3-, ClO4-, SCN-, SO4(2-), F-, Br-, H2PO4-) are measured to be < 10(-3). Of all anions tested, only salicylate yields a slightly greater response than chloride. This selectivity is shown to be adequate for reversible and accurate sensing of chloride levels in diluted serum samples.

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

“…This was observed when a 1:1 molar ratio of each compound was present (Fig. 2) [24][25][26], this was not observed in the present studies.…”

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

“…It is well known that most membrane electrodes based on metalloporhyrin ionophores have significant response to hydroxide ions [28,29]. Hydroxide has a great affinity to the metal ion center of examined metalloporphyrins (logK F-,OH-= 6.6, 6.9, 7.0 and 7.5 for electrodes 1, 9, 14 and 22 respectively) replacing the counterion of metalloporphyrin when in contact with water [30].…”

Aluminum(III) Porphyrins as Ionophores for Fluoride Selective Polymeric Membrane Electrodes

“…It has been reported that other group 13 metalloporphyrins (Ga(III) and In(III)) form hydroxy-bridged dimer species [32], and that selective cleavage of these dimers by analyte ions (F À for Ga(III) and Cl À for In(III)) is responsible for the observed non-Nernstian behavior. [33] Indeed, such dimer - monomer chemistry has already been employed to construct optical sensors for chloride [34] and gaseous amines [35] since the dimeric and monomeric forms of the porphyrins exhibit significant differences in their l max for UV-Vis absorption. For the aluminum(III) porphyrin systems reported here, membrane electrodes equilibrated and conditioned with 10 mM fluoride (added to the internal solution, electrodes VIII and XII) display near-Nernstian fluoride response (see Fig.…”