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Application of Metallocomplexes as Ionophores in Various Polymer Matrices
Available online at www.sciencedirect.com
Procedia Engineering 47 (2012) 672 – 675
Proc. Eurosensors XXVI, September 9-12, 2012, Kraków, Poland
Application of metallocomplexes as ionophores in various polymer matrices Mariusz Pietrzak*, Agnieszka Bala, Monika Mroczkiewicz, Elżbieta Malinowskaa Department of Microbioanalytics, Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, Warsaw 00-664, Poland
Abstract In the framework of presented studies, various metallocomplexes (mainly metalloporphyrins) have been tested in plasticized aminated or carboxylated poly(vinyl chloride) (PVC) and unplasticized polyurethane instead of usually used plasticized PVC-based membranes. Such modification allows for relatively simple preparation of miniaturized planar electrodes (thanks to good adhesion of these membranes to certain substrates) or immobilization of biomolecules to prepare biosensors (thanks to functional groups of applied polymers). It was found, that the presence of functional groups of applied polymers can influence the complexing properties of tested ionophores and consequently the working parameters of ion-selective electrodes prepared with their use. © 2012 The Authors. Published by Elsevier Ltd. Selection and/or peer-review under responsibility of the Symposium Cracoviense © 2012 Published by Elsevier Ltd. Sp. z.o.o.
Keywords: metalloporphyrins, anion-selective electrodes, polyurethane, functionalized poly(vinyl chloride)
1. Introduction Ion-selective electrodes (ISEs) have proved to be valuable analytical tools allowing for fast and cheap analysis of many ionic species [1]. In case of polymer membrane-based ISEs - the group, which is the most frequently studied and has the biggest range of applications (among all ISEs), the most important component of ion-selective membrane is an ionophore. Ionophore is responsible for selective complexation of target ion, which assures the appropriate functioning of electrodes, even in samples of complex matrices. The polymer materials, which give the appropriate physical properties of membranes are usually chemically inert and do not influence the selectivity neither other working parameters of ISEs.
* Corresponding author. Tel.: +48-22-234-7573; fax:+48-22-234-5631. E-mail address: [email protected].
1877-7058 © 2012 The Authors. Published by Elsevier Ltd. Selection and/or peer-review under responsibility of the Symposium Cracoviense Sp. z.o.o. doi:10.1016/j.proeng.2012.09.236
Mariusz Pietrzak et al. / Procedia Engineering 47 (2012) 672 – 675
However, when preparing the miniaturized ISEs or enzymatic biosensor based on ISEs, such inertness can be considered as a significant drawback. The presence of functional groups in a backbone of applied polymers can distinctly influence the properties of membranes, increasing the adhesion to various substrates (particularly important for miniaturization of ISEs in a planar variant) and allowing for biomolecule (enzymes, antibodies, aptamers, etc.) immobilization on their surface [2,3]. Unfortunately, the functional groups of applied polymers are also capable of interaction with ionophores present in a membrane phase, influencing their complexing abilities. Moreover, the working parameters of electrodes prepared with the use of polymers bearing such functionalities can be also altered in comparison with electrodes based on unmodified PVC doped with the same ionophores. 2. Experimental The compounds: chloro 2,7,12,17-tetra-tert-butyl-5,10,15,20-tetraazaporphine aluminum(III) (AlTAP) - described as F-selective ionophore [4], chloro 5,10,15,20-tetrakis(4-t-butylphenyl)porphyrin aluminum(III) (AlBTPP) - described as F-selective ionophore [5], dichloro 5,10,15,20-tetrakis(4-tbutylphenyl)porphyrin zirconium(IV) (ZrBTPP) - described as F-selective ionophore [5], chloro 5,10,15,20-tetrakisphenylporphyrin gallium(III) (GaTPP) - described as F-selective ionophore [6], 5,10,15,20-tetrakisphenylporphyrin nickel(II) (NiTPP) - described as SCN-selective ionophore [7], dichloro 5,10,15,20-tetrakisphenylporphyrin tin(IV) - described as salicylate-selective ionophore [8], chloro 5,10,15,20-tetrakisphenylporphyrin manganese(III) (MnTPP) - described as SCN-selective ionophore [9], chloro 2,3,7,8,12,13,17,18-octaethylporphyrin chromium(III) (CrOEP) - chromium complexes described as salicylate-selective ionophore [10] and chloro 2,3,7,8,12,13,17,18octaethylporphyrin indium(III) (InOEP) - described as Cl-selective ionophore [11] were chosen as anionselective ionophores. For preparation of polymeric ion-selective membranes carboxylated poly(vinyl chloride) (cPVC) (1.8% carboxyl basis), aminated poly(vinyl chloride) (0,79% N of product), polyurethane (PU, Tecoflex SG-80A), o-nitrophenyloctyl ether (o-NPOE), dioctylsebacate (DOS), potassium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (KTFPB) and tetrahydrofuran (THF) were used. For preparation of buffer solutions, glycine (Gly) and orthophosporic acid were used. The ion-selective membranes based on functionalized PVC contained 1 wt.% of ionophore in a carboxylated or aminated PVC:plasticizer (1:2) polymeric matrix. The ion-selective membranes based on PU consisted of 1 wt.% of and 99 wt.% of PU. Some of the ion-selective membranes were also doped with anionic additives. All components were dissolved in 2 mL of THF and the mixture was then transferred to a glass ring (24 mm i.d) mounted on a glass slide. The solvent was allowed to evaporate overnight. Discs (5 mm o.d.) were then cut out from the parent membrane and mounted into Philips electrode bodies (ISE – 561) (Glasblaserei, W. Moller AG, Zurich, Switzerland). The performance of the electrodes was examined by measuring the cell EMF for aqueous solutions of given anions (sodium salts) over the concentration range of 10-7-10-1 mol·dm-3 in buffer solution (0.05 M Gly/H3PO4 buffer, pH 3.0 was used). 3. Results and discussion All of the prepared electrodes based on aminated PVC membranes shown anionic response (see table 1). However, the chemical nature of primary amine groups influenced the working parameters of electrodes with membranes doped with of examined metallocomplexes. When comparing the calibration curves of electrodes with membranes formulated with unmodified PCV (with no additives) with electrodes with membranes formulated with aminated PCV, one can observe shifting of selectivity in favor of more lipophilic anions for aPVC-based electrodes (however, still distinct from Hofmeister series). The amine groups present in a backbone of aPVC can undergo protonation (pH 3.0 was applied),
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Mariusz Pietrzak et al. / Procedia Engineering 47 (2012) 672 – 675
Table 1. The influence of a membrane material on complexing ability of tested metallocomplexes.
Ionophore Membrane
AlTAP
AlBTPP
GaTPP
ZrBTPP
InOEP
MnTPP
CrOEP
SnTPP
NiTPP
aPVC
+
+
+
+
+
+
+
+
h
cPVC
+
+
-
-
-
+
+
-
-
'+' - ionophore works, '-' - ionophore does not work (no response), 'h' - ionophore does not work (selectivity pattern according to Hofmeister series)
hereby becoming the anion-exchanger. For NiTPP the influence of aPVC was so pronounced, that the NiTPP-based electrode exhibited selectivity corresponding to Hofmeister series. The effect of amine groups on ionophores could be neutralized by addition of anionic sites to the membranes. Fig.1. shows the influence of KTFPB addition to the aPVC-base membranes doped with AlBTPP, AlTAP or ZrBTPP on selectivity of electrodes prepared with the use of these ionophores. As it is easy to observe, the higher the KTFPB concentration (up to some limit), the smaller is the influence of lipophilic anions on electrodes' response. 3
2
AlTAP
AlBTPP
ZrBTPP SCN-
1
F,Y
-1
pot
log K
F0
F-
F-
ClO4-
SCNSCN-
-2
NO3Cl -
NO3-3
ClO4-
Br-
ClO4NO3BrCl -
Br-
Cl -
-4 aPVC 50% 100% 150% KTFPB KTFPB KTFPB
aPVC 50% KTFPB
100% KTFPB
150% aPVC 50% KTFPB KTFPB
100% KTFPB
150% KTFPB
Fig. 1. Potentiometric selectivity coefficients of electrodes based on aPVC doped with AlBTPP, AlTAP, ZrBTPP and KTFPB (mol.% according to ionophore).
In contrary to membranes prepared from aminated PVC, only few ionophores (among tested) exhibited useful properties in carboxylated PVC membranes. In case of electrodes with cPVC membranes doped with GaTPP, ZrBTPP, InOEP, GaTPP or NiTPP no anionic response was observed. These electrodes shown only cationic response for high concentration (usually over 10-2 M) of salts used for calibrations (response towards sodium cation). The carboxylic groups present in the polymer structure can function as anionic additives, in some cases suppressing (due to their big amount) the complexing ability of
Mariusz Pietrzak et al. / Procedia Engineering 47 (2012) 672 – 675
ionophores, but in other improving the working parameters of electrodes such as selectivity or detection limit (in comparison with unmodified PVC). Moreover, the carboxylic anion is also capable of direct interaction with metallic centers of ionophores, which can be also reflected as a complete lack of anion response. The compounds based on Al3+, Mn3+ and Cr3+ can be successfully used as ionophores in cPVCbased membranes. While for CrOEP and MnTPP, the replacement of PVC with cPVC reflected as only tiny shift in selectivity, in the case of AlTAP and AlBTPP (F-selective ionophores) the effect of such replacement was more distinct. The selectivity coefficients (KF,Y) against the most lipophilic anions such as thiocynate and perchlorate were lower about one order of magnitude when polymer was changed from PVC to cPVC. The experiments carried out for unplasticized PU-based membranes revealed that anion response of some of the tested ionophores is blocked in such membranes. However, among others Al3+-complexes could be successfully used as ionophores in such membranes.
Acknowledgements This work has been financially supported by Warsaw University of Technology
References
[1] Bühlmann P, Pretsch , Bakker E. Carrier-based ion-selective electrodes and bulk optodes. 2. Ionophores for potentiometric and optical sensors. Chem Rev 1998;98: 1593-687. [2] Leszczyńska E, Gła̧b S, Sokół A, Dziȩgielewski K, Rokicka, Koncki R. Potentiometric biosensor for control of biotechnological production of penicillin G. Anal Chim Acta 1998;368:205-10. [3] Cosofret VV, Erdosy, Buck RP, Kao WJ, Anderson JM, Lindner E, Neuman MR. Electroanalytical and biocompatibility studies on carboxylated poly(vinyl chloride) membranes for microfabricated array sensors. Analyst 1994;119:2283-92. [4] Górski Ł, Mroczkiewicz M, Pietrzak M, Malinowska E. Complexes of tetra-tert-butyl-tetraazaporphine with Al(III) and Zr(IV) cations as fluoride selective ionophores. Anal Chim Acta 2009;633:181-7. [5] Pietrzak M, Meyerhoff ME, Malinowska E. Polymeric membrane electrodes with improved fluoride selectivity and lifetime based on Zr(IV)- and Al(III)-tetraphenylporphyrin derivatives. Anal Chim Acta 2007;596:201-9. [6] Steinle ED, Schaller U, Meyerhoff ME. Response Characteristics of Anion-Selective Polymer Membrane Electrodes Based on Gallium(III), Indium(III) and Thallium(III) Porphyrins. Anal Sci1998;14:79-84. [7] Amini MK, Shahrokhian S, Tangestaninejad S. Thiocyanate-selective electrodes based on nickel and iron phthalocyanines. Anal Chim Acta 1999;402:137-43. [8] Chaniotakis NA, Park S., Meyerhoff ME. Salicylate-selective membrane electrode based on tin(IV) tetraphenylporphyrin. Anal Chem 1989;61:566-70. [9] Khorasani JH, Amini MK, Motagui H, Tangestaninejad S, Moghamad M. Manganese porphyrin derivatives as ionophores for thiocyanate-selective electrodes: The influence of porphyrin substituents and additives on the response properties. Sens Actuat B 2002;87:448-56. [10] Shahrokhian S, Hamzehloei A, Bagherzadeh M. Chromium(III) porphyrin as a selective ionophore in a salicylate-selective membrane electrode. Anal Chem 2002;74:3312-20. [11] Steinle ED, Amemiya S, Bühlmann P, Meyerhoff ME. Origin of non-Nernstian anion response slopes of metalloporphyrinbased liquid/polymer membrane electrodes. Anal Chem 2000;72:5766-73.
675
Procedia Engineering 47 (2012) 672 – 675
Proc. Eurosensors XXVI, September 9-12, 2012, Kraków, Poland
Application of metallocomplexes as ionophores in various polymer matrices Mariusz Pietrzak*, Agnieszka Bala, Monika Mroczkiewicz, Elżbieta Malinowskaa Department of Microbioanalytics, Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, Warsaw 00-664, Poland
Abstract In the framework of presented studies, various metallocomplexes (mainly metalloporphyrins) have been tested in plasticized aminated or carboxylated poly(vinyl chloride) (PVC) and unplasticized polyurethane instead of usually used plasticized PVC-based membranes. Such modification allows for relatively simple preparation of miniaturized planar electrodes (thanks to good adhesion of these membranes to certain substrates) or immobilization of biomolecules to prepare biosensors (thanks to functional groups of applied polymers). It was found, that the presence of functional groups of applied polymers can influence the complexing properties of tested ionophores and consequently the working parameters of ion-selective electrodes prepared with their use. © 2012 The Authors. Published by Elsevier Ltd. Selection and/or peer-review under responsibility of the Symposium Cracoviense © 2012 Published by Elsevier Ltd. Sp. z.o.o.
Keywords: metalloporphyrins, anion-selective electrodes, polyurethane, functionalized poly(vinyl chloride)
1. Introduction Ion-selective electrodes (ISEs) have proved to be valuable analytical tools allowing for fast and cheap analysis of many ionic species [1]. In case of polymer membrane-based ISEs - the group, which is the most frequently studied and has the biggest range of applications (among all ISEs), the most important component of ion-selective membrane is an ionophore. Ionophore is responsible for selective complexation of target ion, which assures the appropriate functioning of electrodes, even in samples of complex matrices. The polymer materials, which give the appropriate physical properties of membranes are usually chemically inert and do not influence the selectivity neither other working parameters of ISEs.
* Corresponding author. Tel.: +48-22-234-7573; fax:+48-22-234-5631. E-mail address: [email protected].
1877-7058 © 2012 The Authors. Published by Elsevier Ltd. Selection and/or peer-review under responsibility of the Symposium Cracoviense Sp. z.o.o. doi:10.1016/j.proeng.2012.09.236
Mariusz Pietrzak et al. / Procedia Engineering 47 (2012) 672 – 675
However, when preparing the miniaturized ISEs or enzymatic biosensor based on ISEs, such inertness can be considered as a significant drawback. The presence of functional groups in a backbone of applied polymers can distinctly influence the properties of membranes, increasing the adhesion to various substrates (particularly important for miniaturization of ISEs in a planar variant) and allowing for biomolecule (enzymes, antibodies, aptamers, etc.) immobilization on their surface [2,3]. Unfortunately, the functional groups of applied polymers are also capable of interaction with ionophores present in a membrane phase, influencing their complexing abilities. Moreover, the working parameters of electrodes prepared with the use of polymers bearing such functionalities can be also altered in comparison with electrodes based on unmodified PVC doped with the same ionophores. 2. Experimental The compounds: chloro 2,7,12,17-tetra-tert-butyl-5,10,15,20-tetraazaporphine aluminum(III) (AlTAP) - described as F-selective ionophore [4], chloro 5,10,15,20-tetrakis(4-t-butylphenyl)porphyrin aluminum(III) (AlBTPP) - described as F-selective ionophore [5], dichloro 5,10,15,20-tetrakis(4-tbutylphenyl)porphyrin zirconium(IV) (ZrBTPP) - described as F-selective ionophore [5], chloro 5,10,15,20-tetrakisphenylporphyrin gallium(III) (GaTPP) - described as F-selective ionophore [6], 5,10,15,20-tetrakisphenylporphyrin nickel(II) (NiTPP) - described as SCN-selective ionophore [7], dichloro 5,10,15,20-tetrakisphenylporphyrin tin(IV) - described as salicylate-selective ionophore [8], chloro 5,10,15,20-tetrakisphenylporphyrin manganese(III) (MnTPP) - described as SCN-selective ionophore [9], chloro 2,3,7,8,12,13,17,18-octaethylporphyrin chromium(III) (CrOEP) - chromium complexes described as salicylate-selective ionophore [10] and chloro 2,3,7,8,12,13,17,18octaethylporphyrin indium(III) (InOEP) - described as Cl-selective ionophore [11] were chosen as anionselective ionophores. For preparation of polymeric ion-selective membranes carboxylated poly(vinyl chloride) (cPVC) (1.8% carboxyl basis), aminated poly(vinyl chloride) (0,79% N of product), polyurethane (PU, Tecoflex SG-80A), o-nitrophenyloctyl ether (o-NPOE), dioctylsebacate (DOS), potassium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (KTFPB) and tetrahydrofuran (THF) were used. For preparation of buffer solutions, glycine (Gly) and orthophosporic acid were used. The ion-selective membranes based on functionalized PVC contained 1 wt.% of ionophore in a carboxylated or aminated PVC:plasticizer (1:2) polymeric matrix. The ion-selective membranes based on PU consisted of 1 wt.% of and 99 wt.% of PU. Some of the ion-selective membranes were also doped with anionic additives. All components were dissolved in 2 mL of THF and the mixture was then transferred to a glass ring (24 mm i.d) mounted on a glass slide. The solvent was allowed to evaporate overnight. Discs (5 mm o.d.) were then cut out from the parent membrane and mounted into Philips electrode bodies (ISE – 561) (Glasblaserei, W. Moller AG, Zurich, Switzerland). The performance of the electrodes was examined by measuring the cell EMF for aqueous solutions of given anions (sodium salts) over the concentration range of 10-7-10-1 mol·dm-3 in buffer solution (0.05 M Gly/H3PO4 buffer, pH 3.0 was used). 3. Results and discussion All of the prepared electrodes based on aminated PVC membranes shown anionic response (see table 1). However, the chemical nature of primary amine groups influenced the working parameters of electrodes with membranes doped with of examined metallocomplexes. When comparing the calibration curves of electrodes with membranes formulated with unmodified PCV (with no additives) with electrodes with membranes formulated with aminated PCV, one can observe shifting of selectivity in favor of more lipophilic anions for aPVC-based electrodes (however, still distinct from Hofmeister series). The amine groups present in a backbone of aPVC can undergo protonation (pH 3.0 was applied),
673
674
Mariusz Pietrzak et al. / Procedia Engineering 47 (2012) 672 – 675
Table 1. The influence of a membrane material on complexing ability of tested metallocomplexes.
Ionophore Membrane
AlTAP
AlBTPP
GaTPP
ZrBTPP
InOEP
MnTPP
CrOEP
SnTPP
NiTPP
aPVC
+
+
+
+
+
+
+
+
h
cPVC
+
+
-
-
-
+
+
-
-
'+' - ionophore works, '-' - ionophore does not work (no response), 'h' - ionophore does not work (selectivity pattern according to Hofmeister series)
hereby becoming the anion-exchanger. For NiTPP the influence of aPVC was so pronounced, that the NiTPP-based electrode exhibited selectivity corresponding to Hofmeister series. The effect of amine groups on ionophores could be neutralized by addition of anionic sites to the membranes. Fig.1. shows the influence of KTFPB addition to the aPVC-base membranes doped with AlBTPP, AlTAP or ZrBTPP on selectivity of electrodes prepared with the use of these ionophores. As it is easy to observe, the higher the KTFPB concentration (up to some limit), the smaller is the influence of lipophilic anions on electrodes' response. 3
2
AlTAP
AlBTPP
ZrBTPP SCN-
1
F,Y
-1
pot
log K
F0
F-
F-
ClO4-
SCNSCN-
-2
NO3Cl -
NO3-3
ClO4-
Br-
ClO4NO3BrCl -
Br-
Cl -
-4 aPVC 50% 100% 150% KTFPB KTFPB KTFPB
aPVC 50% KTFPB
100% KTFPB
150% aPVC 50% KTFPB KTFPB
100% KTFPB
150% KTFPB
Fig. 1. Potentiometric selectivity coefficients of electrodes based on aPVC doped with AlBTPP, AlTAP, ZrBTPP and KTFPB (mol.% according to ionophore).
In contrary to membranes prepared from aminated PVC, only few ionophores (among tested) exhibited useful properties in carboxylated PVC membranes. In case of electrodes with cPVC membranes doped with GaTPP, ZrBTPP, InOEP, GaTPP or NiTPP no anionic response was observed. These electrodes shown only cationic response for high concentration (usually over 10-2 M) of salts used for calibrations (response towards sodium cation). The carboxylic groups present in the polymer structure can function as anionic additives, in some cases suppressing (due to their big amount) the complexing ability of
Mariusz Pietrzak et al. / Procedia Engineering 47 (2012) 672 – 675
ionophores, but in other improving the working parameters of electrodes such as selectivity or detection limit (in comparison with unmodified PVC). Moreover, the carboxylic anion is also capable of direct interaction with metallic centers of ionophores, which can be also reflected as a complete lack of anion response. The compounds based on Al3+, Mn3+ and Cr3+ can be successfully used as ionophores in cPVCbased membranes. While for CrOEP and MnTPP, the replacement of PVC with cPVC reflected as only tiny shift in selectivity, in the case of AlTAP and AlBTPP (F-selective ionophores) the effect of such replacement was more distinct. The selectivity coefficients (KF,Y) against the most lipophilic anions such as thiocynate and perchlorate were lower about one order of magnitude when polymer was changed from PVC to cPVC. The experiments carried out for unplasticized PU-based membranes revealed that anion response of some of the tested ionophores is blocked in such membranes. However, among others Al3+-complexes could be successfully used as ionophores in such membranes.
Acknowledgements This work has been financially supported by Warsaw University of Technology
References
[1] Bühlmann P, Pretsch , Bakker E. Carrier-based ion-selective electrodes and bulk optodes. 2. Ionophores for potentiometric and optical sensors. Chem Rev 1998;98: 1593-687. [2] Leszczyńska E, Gła̧b S, Sokół A, Dziȩgielewski K, Rokicka, Koncki R. Potentiometric biosensor for control of biotechnological production of penicillin G. Anal Chim Acta 1998;368:205-10. [3] Cosofret VV, Erdosy, Buck RP, Kao WJ, Anderson JM, Lindner E, Neuman MR. Electroanalytical and biocompatibility studies on carboxylated poly(vinyl chloride) membranes for microfabricated array sensors. Analyst 1994;119:2283-92. [4] Górski Ł, Mroczkiewicz M, Pietrzak M, Malinowska E. Complexes of tetra-tert-butyl-tetraazaporphine with Al(III) and Zr(IV) cations as fluoride selective ionophores. Anal Chim Acta 2009;633:181-7. [5] Pietrzak M, Meyerhoff ME, Malinowska E. Polymeric membrane electrodes with improved fluoride selectivity and lifetime based on Zr(IV)- and Al(III)-tetraphenylporphyrin derivatives. Anal Chim Acta 2007;596:201-9. [6] Steinle ED, Schaller U, Meyerhoff ME. Response Characteristics of Anion-Selective Polymer Membrane Electrodes Based on Gallium(III), Indium(III) and Thallium(III) Porphyrins. Anal Sci1998;14:79-84. [7] Amini MK, Shahrokhian S, Tangestaninejad S. Thiocyanate-selective electrodes based on nickel and iron phthalocyanines. Anal Chim Acta 1999;402:137-43. [8] Chaniotakis NA, Park S., Meyerhoff ME. Salicylate-selective membrane electrode based on tin(IV) tetraphenylporphyrin. Anal Chem 1989;61:566-70. [9] Khorasani JH, Amini MK, Motagui H, Tangestaninejad S, Moghamad M. Manganese porphyrin derivatives as ionophores for thiocyanate-selective electrodes: The influence of porphyrin substituents and additives on the response properties. Sens Actuat B 2002;87:448-56. [10] Shahrokhian S, Hamzehloei A, Bagherzadeh M. Chromium(III) porphyrin as a selective ionophore in a salicylate-selective membrane electrode. Anal Chem 2002;74:3312-20. [11] Steinle ED, Amemiya S, Bühlmann P, Meyerhoff ME. Origin of non-Nernstian anion response slopes of metalloporphyrinbased liquid/polymer membrane electrodes. Anal Chem 2000;72:5766-73.
675