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, 598 (2), 295-303

Optical Fluoride Sensor Based on Monomer-Dimer Equilibrium of scandium(III)-octaethylporphyrin in a Plasticized Polymeric Film

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Optical Fluoride Sensor Based on Monomer-Dimer Equilibrium of scandium(III)-octaethylporphyrin in a Plasticized Polymeric Film

Youngjea Kang et al. Anal Chim Acta.

Abstract

A fluoride-selective optical sensor based on scandium(III)-octaethylporphyrin (Sc(III)OEP) as an ionophore within a plasticized PVC film is described. The presence of fluoride ion in the aqueous sample phase increases the formation of a difluoro-bridged Sc(III)OEP dimer species in the polymer film. The ability of the Sc(III) porphyrin to form the dimeric structure in the presence of fluoride is confirmed by UV-vis spectroscopy and X-ray crystallography. For more practical sensing applications, a pH chromoionophore (ETH 7075) is added to the plasticized PVC film along with Sc(III)OEP and the observed optical response is based on coextraction of protons with sample phase fluoride to create the dimeric porphyrin and a protonated chromoionophore species. The selectivity pattern observed is F- >> ClO4(-), SCN-, NO3(-) > Br-, Cl-. Only organic salicylate is a significant interferent. Fast and reversible fluoride response is observed over the range of 10(-4) to 10(-2) M fluoride, allowing use of the sensing film in a waveguide configuration for flow-injection measurements.

Figures

Figure 1
Figure 1
Structures of (a) bis(μ-hydroxide) dimer of Sc(III)OEP and (b) ETH 7075.
Figure 1
Figure 1
Structures of (a) bis(μ-hydroxide) dimer of Sc(III)OEP and (b) ETH 7075.
Figure 2
Figure 2
(a) Absorbance of Sc(III)OEP in different concentrations in the o-NPOE/PVC films when the film is conditioned pH 3.0 Gly-phosphate buffer (0.05 M). (b) Absorbance change of Sc(III)OEP upon fluoride response at pH 3.0 with the film Sc(III)OEP(OH) (1wt%)/o-NPOE (66 wt%)/PVC (33 wt%).
Figure 2
Figure 2
(a) Absorbance of Sc(III)OEP in different concentrations in the o-NPOE/PVC films when the film is conditioned pH 3.0 Gly-phosphate buffer (0.05 M). (b) Absorbance change of Sc(III)OEP upon fluoride response at pH 3.0 with the film Sc(III)OEP(OH) (1wt%)/o-NPOE (66 wt%)/PVC (33 wt%).
Figure 3
Figure 3
crystal structure of bis(μ-fluoro) dimer of Sc(III)OEP (left). Diagram of structural characteristics of [Sc(III)OEP]2(μ-F)2 (right).
Figure 4
Figure 4
Response curves for anions (chloride (■), bromide (×), nitrate (*), thiocyanate (●), perchlorate (◆), salicylate (▲), and fluoride (+)) in (a) DOS/PVC film and (b) o-NPOE/PVC film. Black points represent experimental data points, and grey lines are based on best-fitting curves for each response. Film compositions : Sc(III)OEP(OH) (1 wt%)/ ETH 7075 (100 mol%) / plasticizer (DOS or o-NPOE 66 wt%)/ PVC (33 wt%).
Figure 4
Figure 4
Response curves for anions (chloride (■), bromide (×), nitrate (*), thiocyanate (●), perchlorate (◆), salicylate (▲), and fluoride (+)) in (a) DOS/PVC film and (b) o-NPOE/PVC film. Black points represent experimental data points, and grey lines are based on best-fitting curves for each response. Film compositions : Sc(III)OEP(OH) (1 wt%)/ ETH 7075 (100 mol%) / plasticizer (DOS or o-NPOE 66 wt%)/ PVC (33 wt%).
Figure 5
Figure 5
Fluoride response (●) at different total fluoride concentration in the 0.05 M Gly-phosphate buffer (pH 3.0) with the film composition : Sc(III)OEP (1 wt%)/ETH 7075 (100 mol%)/o-NPOE (66 wt%)/PVC(33 wt%) and theoretical response curves based on rxn. 2 and rxn. 3.
Figure 6
Figure 6
Spectral shift of Sc(III)OEP/ETH 7075/NPOE/PVC film upon (a) fluoride and (b) salicylate responses. Absorbance change at 550 nm is attributed to both anions, while absorbance change at 393 nm is solely by fluoride response.
Figure 6
Figure 6
Spectral shift of Sc(III)OEP/ETH 7075/NPOE/PVC film upon (a) fluoride and (b) salicylate responses. Absorbance change at 550 nm is attributed to both anions, while absorbance change at 393 nm is solely by fluoride response.
Figure 7
Figure 7
Reversible response (550 nm) to fluoride between 10-4 M and 10-2 M in (a) DOS/PVC film and (b) o-NPOE/PVC film.
Figure 7
Figure 7
Reversible response (550 nm) to fluoride between 10-4 M and 10-2 M in (a) DOS/PVC film and (b) o-NPOE/PVC film.

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