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Analytica Chimica Acta (v.591, #1)
Benefit of liquid crystal moieties in the MIP technique by Corinne Binet; Sandrine Ferrère; Armand Lattes; Elisabeth Laurent; Jean-Daniel Marty; Monique Mauzac; Anne-Françoise Mingotaud; Guillaume Palaprat; Marie Weyland (pp. 1-6).
Several liquid crystalline imprinted materials have been synthesized from polysiloxanes or polyacrylates bearing mesogenic side-chains and low contents of cross-linkers. They were imprinted by various achiral or chiral templates, then tested for molecular recognition or assessed as specific catalysts. All mesogenic imprinted networks exhibit a much higher affinity towards the template than non-imprinted networks. On the other hand, the molecular trapping capacity was shown to be much greater than that of most of the previously studied non-mesomorphous systems. Moreover, it was shown that mesomorphic order provides significant enhancement to the bonding between the template and the liquid crystalline network and reinforces the shape memory of the imprinted cavities. Some of these materials were used to catalyze the isomerization of benzisoxazole. They exhibited an acceleration effect close to 100 between imprinted sites and non-imprinted ones. Lastly, cholesteric networks, that were imprinted by a chiral template, showed good properties for the enantiomer separation leading to an enantiomeric excess of 35% and a capacity of around 1mmolg−1.
Keywords: Liquid crystal; Molecular imprinted polymers; Enantiomer separation; Catalysis; Sensors
Benefit of liquid crystal moieties in the MIP technique by Corinne Binet; Sandrine Ferrère; Armand Lattes; Elisabeth Laurent; Jean-Daniel Marty; Monique Mauzac; Anne-Françoise Mingotaud; Guillaume Palaprat; Marie Weyland (pp. 1-6).
Several liquid crystalline imprinted materials have been synthesized from polysiloxanes or polyacrylates bearing mesogenic side-chains and low contents of cross-linkers. They were imprinted by various achiral or chiral templates, then tested for molecular recognition or assessed as specific catalysts. All mesogenic imprinted networks exhibit a much higher affinity towards the template than non-imprinted networks. On the other hand, the molecular trapping capacity was shown to be much greater than that of most of the previously studied non-mesomorphous systems. Moreover, it was shown that mesomorphic order provides significant enhancement to the bonding between the template and the liquid crystalline network and reinforces the shape memory of the imprinted cavities. Some of these materials were used to catalyze the isomerization of benzisoxazole. They exhibited an acceleration effect close to 100 between imprinted sites and non-imprinted ones. Lastly, cholesteric networks, that were imprinted by a chiral template, showed good properties for the enantiomer separation leading to an enantiomeric excess of 35% and a capacity of around 1mmolg−1.
Keywords: Liquid crystal; Molecular imprinted polymers; Enantiomer separation; Catalysis; Sensors
Shape selectivity versus functional group pre-organization in molecularly imprinted polymers by Ryan Simon; Melissa E. Collins; David A. Spivak (pp. 7-16).
A systematic survey of related molecular probes differing in shape or functional group orientation was used to compare the effects of shape selectivity versus pre-organization of functional monomers on imprinting and rebinding performance of molecularly imprinted polymers (MIPs). These studies revealed that templates with two functional group interactions with the MIPs are influenced to a larger degree by shape selective interactions than templates with three functional group interactions. For example, with two functional group interactions, increasing side chain size of compounds1–5 increased selectivity 5-fold; while the same size change for compounds with three functional group interactions leads to a maximum 2-fold increase. Thus, the effects of shape selectivity and pre-organization of functional groups do not appear to work in concert with each other during the imprinting process or in the rebinding behavior. Furthermore, greater selectivity is generally found for templates with two functional groups, where the dominant mode of molecular recognition is shape selectivity. For example, the α value for the MIP elicited toward template compound5 with two hydrogen bonding groups was 5–12-fold higher than equivalently shaped compounds6–8 that have three non-covalent binding interactions (Table 3). On the other hand, pre-organization of functional groups dominated the performance of MIPs elicited toward templates with three template–functional group interactions. This is observed in Tables 6–8, where compounds with identical positioning of three functional groups all show less than an order of magnitude change in α values despite changes in shape.
Keywords: Molecularly imprinted polymers; Shape selectivity; Pre-organization; Structure-binding relationship; Molecular recognition
Shape selectivity versus functional group pre-organization in molecularly imprinted polymers by Ryan Simon; Melissa E. Collins; David A. Spivak (pp. 7-16).
A systematic survey of related molecular probes differing in shape or functional group orientation was used to compare the effects of shape selectivity versus pre-organization of functional monomers on imprinting and rebinding performance of molecularly imprinted polymers (MIPs). These studies revealed that templates with two functional group interactions with the MIPs are influenced to a larger degree by shape selective interactions than templates with three functional group interactions. For example, with two functional group interactions, increasing side chain size of compounds1–5 increased selectivity 5-fold; while the same size change for compounds with three functional group interactions leads to a maximum 2-fold increase. Thus, the effects of shape selectivity and pre-organization of functional groups do not appear to work in concert with each other during the imprinting process or in the rebinding behavior. Furthermore, greater selectivity is generally found for templates with two functional groups, where the dominant mode of molecular recognition is shape selectivity. For example, the α value for the MIP elicited toward template compound5 with two hydrogen bonding groups was 5–12-fold higher than equivalently shaped compounds6–8 that have three non-covalent binding interactions (Table 3). On the other hand, pre-organization of functional groups dominated the performance of MIPs elicited toward templates with three template–functional group interactions. This is observed in Tables 6–8, where compounds with identical positioning of three functional groups all show less than an order of magnitude change in α values despite changes in shape.
Keywords: Molecularly imprinted polymers; Shape selectivity; Pre-organization; Structure-binding relationship; Molecular recognition
Which molecularly imprinted polymer is better? by B. Tóth; T. Pap; V. Horvath; G. Horvai (pp. 17-21).
Molecularly imprinted polymers (MIP) have been successfully synthesized toward many different compounds in the last decades. The mechanistic details of selective binding at binding sites are not yet well understood. For this reason the characterization of MIP binding has been mostly phenomenological and this makes the transfer of results between different laboratories or between different types of applications difficult. In this paper we analyze the relationship between different types of characterization like isotherms, binding site models, chromatographic k and α values, etc. as they relate to different applications like HPLC, solid phase extraction (SPE), binding assays, batch extraction and sensors. It is shown that α values determined by elution chromatography depend on seemingly irrelevant factors as the length and diameter of the column, respectively. The determination of distribution ratios or partition coefficients is proposed as an easily understandable and useful quantity in the characterization of novel MIPs. Data used for the characterization of a MIP should be transferable between different applications but the qualification of MIPs as better or worse will depend on the application in case.
Keywords: Molecularly imprinted polymer; Distribution ratio; Partition coefficient; Isotherm
Which molecularly imprinted polymer is better? by B. Tóth; T. Pap; V. Horvath; G. Horvai (pp. 17-21).
Molecularly imprinted polymers (MIP) have been successfully synthesized toward many different compounds in the last decades. The mechanistic details of selective binding at binding sites are not yet well understood. For this reason the characterization of MIP binding has been mostly phenomenological and this makes the transfer of results between different laboratories or between different types of applications difficult. In this paper we analyze the relationship between different types of characterization like isotherms, binding site models, chromatographic k and α values, etc. as they relate to different applications like HPLC, solid phase extraction (SPE), binding assays, batch extraction and sensors. It is shown that α values determined by elution chromatography depend on seemingly irrelevant factors as the length and diameter of the column, respectively. The determination of distribution ratios or partition coefficients is proposed as an easily understandable and useful quantity in the characterization of novel MIPs. Data used for the characterization of a MIP should be transferable between different applications but the qualification of MIPs as better or worse will depend on the application in case.
Keywords: Molecularly imprinted polymer; Distribution ratio; Partition coefficient; Isotherm
Chromatographic characterisation, under highly aqueous conditions, of a molecularly imprinted polymer binding the herbicide 2,4-dichlorophenoxyacetic acid by C. Legido-Quigley; J. Oxelbark; E. De Lorenzi; A. Zurutuza-Elorza; P.A.G. Cormack (pp. 22-28).
The affinity of a 2,4-dichlorophenoxyacetic acid (2,4-D) molecularly imprinted polymer (MIP), which was synthesised directly in an aqueous organic solvent, for its template (2,4-D) was studied and compared with the affinity exhibited by two other reference (control) polymers, NIPA and NIPB, for the same analyte. Zonal chromatography was performed to establish the optimal selectivity, expressed as imprinting factor (IF), under chromatographic conditions more aqueous than those described so far in the literature. Frontal analysis (FA) was performed on columns packed with these polymers, using an optimized mobile phase composed of methanol/phosphate buffer (50/50, v/v), to extract adsorption isotherm data and retrieve binding parameters from the best isotherm model. Surprisingly, the template had comparable and strong affinity for both MIP ( K=3.8×104M−1) and NIPA ( K=1.9×104M−1), although there was a marked difference in the saturation capacities of selective and non-selective sites, as one would expect for an imprinted polymer. NIPB acts as a true control polymer in the sense that it has relatively low affinity for the template ( K=8.0×102M−1). This work provides the first frontal chromatographic characterization of such a polymer in a water-rich environment over a wide concentration range. The significance of this work stems from the fact that the chromatographic approach used is generic and can be applied readily to other analytes, but also because there is an increasing demand for well-characterised imprinted materials that function effectively in aqueous media and are thus well-suited for analytical science applications involving, for example, biofluids and environmental water samples.
Keywords: Molecular imprinting; 2,4-Dichlorophenoxyacetic acid; Frontal chromatography; Adsorption isotherm
Chromatographic characterisation, under highly aqueous conditions, of a molecularly imprinted polymer binding the herbicide 2,4-dichlorophenoxyacetic acid by C. Legido-Quigley; J. Oxelbark; E. De Lorenzi; A. Zurutuza-Elorza; P.A.G. Cormack (pp. 22-28).
The affinity of a 2,4-dichlorophenoxyacetic acid (2,4-D) molecularly imprinted polymer (MIP), which was synthesised directly in an aqueous organic solvent, for its template (2,4-D) was studied and compared with the affinity exhibited by two other reference (control) polymers, NIPA and NIPB, for the same analyte. Zonal chromatography was performed to establish the optimal selectivity, expressed as imprinting factor (IF), under chromatographic conditions more aqueous than those described so far in the literature. Frontal analysis (FA) was performed on columns packed with these polymers, using an optimized mobile phase composed of methanol/phosphate buffer (50/50, v/v), to extract adsorption isotherm data and retrieve binding parameters from the best isotherm model. Surprisingly, the template had comparable and strong affinity for both MIP ( K=3.8×104M−1) and NIPA ( K=1.9×104M−1), although there was a marked difference in the saturation capacities of selective and non-selective sites, as one would expect for an imprinted polymer. NIPB acts as a true control polymer in the sense that it has relatively low affinity for the template ( K=8.0×102M−1). This work provides the first frontal chromatographic characterization of such a polymer in a water-rich environment over a wide concentration range. The significance of this work stems from the fact that the chromatographic approach used is generic and can be applied readily to other analytes, but also because there is an increasing demand for well-characterised imprinted materials that function effectively in aqueous media and are thus well-suited for analytical science applications involving, for example, biofluids and environmental water samples.
Keywords: Molecular imprinting; 2,4-Dichlorophenoxyacetic acid; Frontal chromatography; Adsorption isotherm
Solid phase extraction of food contaminants using molecular imprinted polymers by Claudio Baggiani; Laura Anfossi; Cristina Giovannoli (pp. 29-39).
Food contamination from natural or anthropogenic sources poses severe risks to human health. It is now largely accepted that continuous exposure to low doses of toxic chemicals can be related to several chronic diseases, including some type of cancer and serious hormonal dysfunctions.Contemporary analytical methods have the sensitivity required for contamination detection and quantification, but direct application of these methods on food samples can be rarely performed. In fact, the matrix introduces severe disturbances, and analysis can be performed only after some clean-up and preconcentration steps. Current sample pre-treatment methods, mostly based on the solid phase extraction technique, are very fast and inexpensive but show a lack of selectivity, while methods based on immunoaffinity extraction are very selective but expensive and not suitable for harsh environments. Thus, inexpensive, rapid and selective clean-up methods, relaying on “intelligent” materials are needed. Recent years have seen a significant increase of the “molecularly imprinted solid phase extraction” (MISPE) technique in the food contaminant analysis. In fact, this technique seems to be particularly suitable for extractive applications where analyte selectivity in the presence of very complex and structured matrices represents the main problem. In this review, several applications of MISPE in food contamination analysis will be discussed, with particular emphasis on the extraction of pesticides, drugs residua, mycotoxins and environmental contaminants.
Keywords: Molecular imprinting; Solid phase extraction; Food analysis; Contaminants; Pesticides; Drugs; Antibiotics; Mycotoxins
Solid phase extraction of food contaminants using molecular imprinted polymers by Claudio Baggiani; Laura Anfossi; Cristina Giovannoli (pp. 29-39).
Food contamination from natural or anthropogenic sources poses severe risks to human health. It is now largely accepted that continuous exposure to low doses of toxic chemicals can be related to several chronic diseases, including some type of cancer and serious hormonal dysfunctions.Contemporary analytical methods have the sensitivity required for contamination detection and quantification, but direct application of these methods on food samples can be rarely performed. In fact, the matrix introduces severe disturbances, and analysis can be performed only after some clean-up and preconcentration steps. Current sample pre-treatment methods, mostly based on the solid phase extraction technique, are very fast and inexpensive but show a lack of selectivity, while methods based on immunoaffinity extraction are very selective but expensive and not suitable for harsh environments. Thus, inexpensive, rapid and selective clean-up methods, relaying on “intelligent” materials are needed. Recent years have seen a significant increase of the “molecularly imprinted solid phase extraction” (MISPE) technique in the food contaminant analysis. In fact, this technique seems to be particularly suitable for extractive applications where analyte selectivity in the presence of very complex and structured matrices represents the main problem. In this review, several applications of MISPE in food contamination analysis will be discussed, with particular emphasis on the extraction of pesticides, drugs residua, mycotoxins and environmental contaminants.
Keywords: Molecular imprinting; Solid phase extraction; Food analysis; Contaminants; Pesticides; Drugs; Antibiotics; Mycotoxins
Hybrid molecular imprinted membranes having selectivity and separation behavior to targeted indole derivatives by Kohei Takeda; Kohei Uemura; Takaomi Kobayashi (pp. 40-48).
Molecular imprinted membrane of indole-3-ethanol (IE) was prepared by hybridization of IE imprinted polymer powder and polysulfone (PSf) membrane. The IE imprinted polymer by covalent imprinting method was synthesized with copolymerization of indole-3-ethyl methacrylate (IEMA) and divinylbenzene (DVB). The cross-linked P(IEMA- co-DVB) was ground to be powders having less than 63μm size and then hybridized within PSf membrane by using phase inversion process. The resultant imprinted powder showed binding capacities of 1.8, 7.2, 0 and 0μmolg−1 for IE, indole, 8-hydroxyquinoline and pyrrole in aqueous solution, respectively, and after hybridization with the PSf membrane, the value was 46, 26, 0 and 0μmolg−1. As a result, it was found that the IE imprinted powder alone showed non-selectively binding to the IE, but, the hybridized powder within the PSf membrane bound selectively the IE. Evidence was presented that hydrophobic interaction of the PSf matrix caused the selective and efficient binding. We also showed separation behavior of the hybrid membranes and discussed on the binding selectivity of the IE molecule. In view point of hybrid effect of the PSf membrane and the cross-linked imprinted powder, the results of the separation of these substrates were considered.
Keywords: Molecular imprinted polymers; Hybrid membrane; Separation; Permeation; Adsorption
Hybrid molecular imprinted membranes having selectivity and separation behavior to targeted indole derivatives by Kohei Takeda; Kohei Uemura; Takaomi Kobayashi (pp. 40-48).
Molecular imprinted membrane of indole-3-ethanol (IE) was prepared by hybridization of IE imprinted polymer powder and polysulfone (PSf) membrane. The IE imprinted polymer by covalent imprinting method was synthesized with copolymerization of indole-3-ethyl methacrylate (IEMA) and divinylbenzene (DVB). The cross-linked P(IEMA- co-DVB) was ground to be powders having less than 63μm size and then hybridized within PSf membrane by using phase inversion process. The resultant imprinted powder showed binding capacities of 1.8, 7.2, 0 and 0μmolg−1 for IE, indole, 8-hydroxyquinoline and pyrrole in aqueous solution, respectively, and after hybridization with the PSf membrane, the value was 46, 26, 0 and 0μmolg−1. As a result, it was found that the IE imprinted powder alone showed non-selectively binding to the IE, but, the hybridized powder within the PSf membrane bound selectively the IE. Evidence was presented that hydrophobic interaction of the PSf matrix caused the selective and efficient binding. We also showed separation behavior of the hybrid membranes and discussed on the binding selectivity of the IE molecule. In view point of hybrid effect of the PSf membrane and the cross-linked imprinted powder, the results of the separation of these substrates were considered.
Keywords: Molecular imprinted polymers; Hybrid membrane; Separation; Permeation; Adsorption
Gas phase detection of explosives such as 2,4,6-trinitrotoluene by molecularly imprinted polymers by Gudrun Bunte; Jürgen Hürttlen; Heike Pontius; Kerstin Hartlieb; Horst Krause (pp. 49-56).
Fast, reliable and inexpensive analytical techniques for trace detection of explosive components are in high demand. Our approach is to develop specific sensor coating materials based on molecularly imprinted polymers (MIPs). Despite the known inhibition of radical polymerisations by nitro groups and the known shrinkage of the polymer lattice during/after drying we were able to synthesize particulate MIPs by suspension polymerisation as well as thin MIP coatings by direct surface polymerisation on quartz crystal microbalances (QCM). The best method to purify the porous beads was Soxhlet extraction followed by supercritical carbon dioxide extraction (SFE with sc-CO2) at mild conditions (150bar, 50°C). At least a removal of >99.7% of the template was achieved. Performance tests of TNT imprinted polymer beads showed that acrylamide (AA) and more pronounced also methacrylic acid (MAA) possessed an enhanced adsorption tendency for gaseous TNT. An adsorption of 2,4-DNT, dinitrotoluene, by these MIPs was not detected. Using 2,4-DNT as template and methacrylamide, MAAM, a positive imprint effect for gaseous 2,4-DNT was achieved with no measurable cross-sensitivity for 2,4,6-TNT.The thin MIP coatings directly synthesized on the QCMs showed thicknesses of 20 to up to 500nm. Preliminary screening experiments were performed for five different monomers and three different solvents (acetonitrile, chloroform and dimethylformamide). Best adsorption properties for TNT vapour until now showed a PAA-MIP synthesized with chloroform. Direct measurements of the mass attachment, respectively frequency decrease of the coated QCMs during vapour treatment showed a TNT-uptake of about 150pg per μg MIP per hour. Results look worthy for further studies.
Keywords: Detection of explosive vapours; Low-cost sensors; Molecularly imprinted polymers (MIP); Quartz crystal microbalance (QCM); Suspension polymerisation; Polymerisation initiated by ultraviolet light (UV)
Gas phase detection of explosives such as 2,4,6-trinitrotoluene by molecularly imprinted polymers by Gudrun Bunte; Jürgen Hürttlen; Heike Pontius; Kerstin Hartlieb; Horst Krause (pp. 49-56).
Fast, reliable and inexpensive analytical techniques for trace detection of explosive components are in high demand. Our approach is to develop specific sensor coating materials based on molecularly imprinted polymers (MIPs). Despite the known inhibition of radical polymerisations by nitro groups and the known shrinkage of the polymer lattice during/after drying we were able to synthesize particulate MIPs by suspension polymerisation as well as thin MIP coatings by direct surface polymerisation on quartz crystal microbalances (QCM). The best method to purify the porous beads was Soxhlet extraction followed by supercritical carbon dioxide extraction (SFE with sc-CO2) at mild conditions (150bar, 50°C). At least a removal of >99.7% of the template was achieved. Performance tests of TNT imprinted polymer beads showed that acrylamide (AA) and more pronounced also methacrylic acid (MAA) possessed an enhanced adsorption tendency for gaseous TNT. An adsorption of 2,4-DNT, dinitrotoluene, by these MIPs was not detected. Using 2,4-DNT as template and methacrylamide, MAAM, a positive imprint effect for gaseous 2,4-DNT was achieved with no measurable cross-sensitivity for 2,4,6-TNT.The thin MIP coatings directly synthesized on the QCMs showed thicknesses of 20 to up to 500nm. Preliminary screening experiments were performed for five different monomers and three different solvents (acetonitrile, chloroform and dimethylformamide). Best adsorption properties for TNT vapour until now showed a PAA-MIP synthesized with chloroform. Direct measurements of the mass attachment, respectively frequency decrease of the coated QCMs during vapour treatment showed a TNT-uptake of about 150pg per μg MIP per hour. Results look worthy for further studies.
Keywords: Detection of explosive vapours; Low-cost sensors; Molecularly imprinted polymers (MIP); Quartz crystal microbalance (QCM); Suspension polymerisation; Polymerisation initiated by ultraviolet light (UV)
Enantioseparation on molecularly imprinted monoliths—Preparation and adsorption isotherms by Axel Seebach; Andreas Seidel-Morgenstern (pp. 57-62).
In this paper we report the synthesis of monolithic molecularly imprinted polymers (monolithic MIPs) for the chromatographic separation of Z-phenylalanine by “in situ” polymerisation. Four different functional monomers were used for the preparation and the columns were tested with a standard mobile phase of 1% acetic acid in acetonitrile. 4-Vinylpyridine has shown the best separation performance with a resolution factorR>1 and was chosen for a further improvement of the imprinted stationary phase, which leads to a resolution factorR=2.06. All monoliths investigated have surface areas of around 400 m2 g−1. The columns containing 4-vinylpyridine as functional monomer were characterised by frontal analysis and peak fitting method. These methods allow the determination of the adsorption isotherm which quantify the separation potential of the imprinted monoliths.
Keywords: Moelcularly imprinted polymers; Enantioseparation; Adsorption isotherms; Peak maximum fitting
Enantioseparation on molecularly imprinted monoliths—Preparation and adsorption isotherms by Axel Seebach; Andreas Seidel-Morgenstern (pp. 57-62).
In this paper we report the synthesis of monolithic molecularly imprinted polymers (monolithic MIPs) for the chromatographic separation of Z-phenylalanine by “in situ” polymerisation. Four different functional monomers were used for the preparation and the columns were tested with a standard mobile phase of 1% acetic acid in acetonitrile. 4-Vinylpyridine has shown the best separation performance with a resolution factorR>1 and was chosen for a further improvement of the imprinted stationary phase, which leads to a resolution factorR=2.06. All monoliths investigated have surface areas of around 400 m2 g−1. The columns containing 4-vinylpyridine as functional monomer were characterised by frontal analysis and peak fitting method. These methods allow the determination of the adsorption isotherm which quantify the separation potential of the imprinted monoliths.
Keywords: Moelcularly imprinted polymers; Enantioseparation; Adsorption isotherms; Peak maximum fitting
Surface plasmon resonance sensor for lysozyme based on molecularly imprinted thin films by Takateru Matsunaga; Takayuki Hishiya; Toshifumi Takeuchi (pp. 63-67).
Molecularly imprinted polymers (MIPs) selective for lysozyme were prepared on SPR sensor chips by radical co-polymerization with acrylic acid and N, N′-methylenebisacrylamide. Gold-coated SPR sensor chips were modified with N, N′-bis(acryloyl)cystamine, on which MIP thin films were covalently conjugated. The presence of NaCl during the polymerization and the re-binding tests affected the selectivity and the optimization of NaCl concentration in the pre-polymerization mixture and the re-binding buffer could enhance the selectivity in the target protein sensing. When the lysozyme-imprinted polymer thin films were prepared in the presence of 40mM NaCl, the selectivity factor (target protein bound/reference protein bound) of MIP in the re-binding buffer containing 20mM NaCl was 9.8, meanwhile, that of MIP in the re-binding buffer without NaCl was 1.2. A combination of SPR sensing technology with protein-imprinted thin films is a promising tool for the construction of selective protein sensors.
Keywords: Molecular imprinting; Protein recognition; Lysozyme; Surface plasmon resonance sensor; Acrylic acid; N; ,; N; ′-Methylenebisacrylamide
Surface plasmon resonance sensor for lysozyme based on molecularly imprinted thin films by Takateru Matsunaga; Takayuki Hishiya; Toshifumi Takeuchi (pp. 63-67).
Molecularly imprinted polymers (MIPs) selective for lysozyme were prepared on SPR sensor chips by radical co-polymerization with acrylic acid and N, N′-methylenebisacrylamide. Gold-coated SPR sensor chips were modified with N, N′-bis(acryloyl)cystamine, on which MIP thin films were covalently conjugated. The presence of NaCl during the polymerization and the re-binding tests affected the selectivity and the optimization of NaCl concentration in the pre-polymerization mixture and the re-binding buffer could enhance the selectivity in the target protein sensing. When the lysozyme-imprinted polymer thin films were prepared in the presence of 40mM NaCl, the selectivity factor (target protein bound/reference protein bound) of MIP in the re-binding buffer containing 20mM NaCl was 9.8, meanwhile, that of MIP in the re-binding buffer without NaCl was 1.2. A combination of SPR sensing technology with protein-imprinted thin films is a promising tool for the construction of selective protein sensors.
Keywords: Molecular imprinting; Protein recognition; Lysozyme; Surface plasmon resonance sensor; Acrylic acid; N; ,; N; ′-Methylenebisacrylamide
Dispersive liquid–liquid microextraction followed by high-performance liquid chromatography-diode array detection as an efficient and sensitive technique for determination of antioxidants by Mir Ali Farajzadeh; Morteza Bahram; Jan Åke Jönsson (pp. 69-79).
Dispersive liquid–liquid microextraction (DLLME) and high performance liquid chromatography-diode array detection (HPLC-DAD) was presented for extraction and determination of Irganox 1010, Irganox 1076 and Irgafos 168 (antioxidants) in aqueous samples. Carbon tetrachloride at microliter volume level and acetonitrile were used as extraction and dispersive solvents, respectively. The main advantages of method are high speed, high enrichment factor, high recovery, good repeatability and extraction solvent volume at μL level. Limit of detection for analytes is between 3 and 7ngmL−1. One variable at a time optimization and response surface modeling were used to obtain optimum conditions for microextraction procedure and nearly same experimental conditions were obtained using both optimization methods. Recoveries in the ranges 78–86% and 84–110% were obtained by one variable at a time and response surface modeling, respectively. Using tap water and packed water as matrices do not show any detrimental effect on the extraction recoveries and enrichment factors of analytes.
Keywords: Dispersive liquid–liquid extraction; Antioxidant; High-performance liquid chromatography; Sample preparation; One variable at a time optimization; Response surface modeling
Dispersive liquid–liquid microextraction followed by high-performance liquid chromatography-diode array detection as an efficient and sensitive technique for determination of antioxidants by Mir Ali Farajzadeh; Morteza Bahram; Jan Åke Jönsson (pp. 69-79).
Dispersive liquid–liquid microextraction (DLLME) and high performance liquid chromatography-diode array detection (HPLC-DAD) was presented for extraction and determination of Irganox 1010, Irganox 1076 and Irgafos 168 (antioxidants) in aqueous samples. Carbon tetrachloride at microliter volume level and acetonitrile were used as extraction and dispersive solvents, respectively. The main advantages of method are high speed, high enrichment factor, high recovery, good repeatability and extraction solvent volume at μL level. Limit of detection for analytes is between 3 and 7ngmL−1. One variable at a time optimization and response surface modeling were used to obtain optimum conditions for microextraction procedure and nearly same experimental conditions were obtained using both optimization methods. Recoveries in the ranges 78–86% and 84–110% were obtained by one variable at a time and response surface modeling, respectively. Using tap water and packed water as matrices do not show any detrimental effect on the extraction recoveries and enrichment factors of analytes.
Keywords: Dispersive liquid–liquid extraction; Antioxidant; High-performance liquid chromatography; Sample preparation; One variable at a time optimization; Response surface modeling
An improved biosensor for acetaldehyde determination using a bienzymatic strategy at poly(neutral red) modified carbon film electrodes by Mariana Emilia Ghica; Rasa Pauliukaite; Nicolas Marchand; Eric Devic; Christopher M.A. Brett (pp. 80-86).
Improved biosensors for acetaldehyde determination have been developed using a bienzymatic strategy, based on a mediator-modified carbon film electrode and co-immobilisation of NADH oxidase and aldehyde dehydrogenase. Modification of the carbon film electrode with poly(neutral red) mediator resulted in a sensitive, low-cost and reliable NADH detector. Immobilisation of the enzymes was performed using encapsulation in a sol–gel matrix or cross-linking with glutaraldehyde. The bienzymatic biosensors were characterized by studying the influence of pH, applied potential and co-factors. The sol–gel and glutaraldehyde biosensors showed a linear response up to 60μM and 100μM, respectively, with detection limits of 2.6μM and 3.3μM and sensitivities were 1.7μAmM−1 and 5.6μAmM−1. The optimised biosensors showed good stability and good selectivity and have been tested for application for the determination of acetaldehyde in natural samples such as wine.
Keywords: Nicotinamide adenine dinucleotide oxidase; Aldehyde dehydrogenase; Carbon film electrode; Poly(neutral red); Enzyme cross-linking; Sol–gel
An improved biosensor for acetaldehyde determination using a bienzymatic strategy at poly(neutral red) modified carbon film electrodes by Mariana Emilia Ghica; Rasa Pauliukaite; Nicolas Marchand; Eric Devic; Christopher M.A. Brett (pp. 80-86).
Improved biosensors for acetaldehyde determination have been developed using a bienzymatic strategy, based on a mediator-modified carbon film electrode and co-immobilisation of NADH oxidase and aldehyde dehydrogenase. Modification of the carbon film electrode with poly(neutral red) mediator resulted in a sensitive, low-cost and reliable NADH detector. Immobilisation of the enzymes was performed using encapsulation in a sol–gel matrix or cross-linking with glutaraldehyde. The bienzymatic biosensors were characterized by studying the influence of pH, applied potential and co-factors. The sol–gel and glutaraldehyde biosensors showed a linear response up to 60μM and 100μM, respectively, with detection limits of 2.6μM and 3.3μM and sensitivities were 1.7μAmM−1 and 5.6μAmM−1. The optimised biosensors showed good stability and good selectivity and have been tested for application for the determination of acetaldehyde in natural samples such as wine.
Keywords: Nicotinamide adenine dinucleotide oxidase; Aldehyde dehydrogenase; Carbon film electrode; Poly(neutral red); Enzyme cross-linking; Sol–gel
Analysis of chloroacetanilide herbicides in water samples by solid-phase microextraction coupled with gas chromatography–mass spectrometry by Xiaoqin Xu; Huanghao Yang; Ling Wang; Bin Han; Xiaoru Wang; Frank Sen-Chun Lee (pp. 87-96).
A solid-phase microextraction (SPME) method has been developed for the determination of 3 chloroacetanilide herbicides in both fresh and seawater samples. The extracted sample was analyzed by gas chromatography with mass spectrometry detection (GC–MS), and parameters affecting SPME operation including fibre type, sample pH, sample temperature, mixing speed and extraction time have been evaluated and optimized. The amount of dissolved organic matter (DOM) and the salt content both affected SPME extraction efficiency, but the presence of other competitive extractants such as organochlorine pesticides (OCPs) in the matrix showed no insignificance interference. The limit of detection (LOD) for acetochlor, metolachlor and butachlor were 1.2, 1.6 and 2.7ngL−1, respectively. The recoveries for the herbicides ranged from 79 to 102%, and the linear dynamic range was from 10 to 1000ngL−1. The developed method has been used to monitor herbicides contaminations in coastal water samples collected around Laizhou bay and Jiaozhou bay in Shandong peninsula, China. The concentrations of acetochlor and metolachlor ranged from undetectable to 78.5ngL−1 and undetectable to 35.6ngL−1, respectively. Butachlor was not observed but in only one sample and the concentration is lower than the limit of quantification (LOQ). The concentrations of the three herbicides in this study are low compared to most of the other places reported.
Keywords: Water analysis; Solid-phase microextraction; Environmental analysis; Herbicides; Gas chromatography–mass spectrometry
Analysis of chloroacetanilide herbicides in water samples by solid-phase microextraction coupled with gas chromatography–mass spectrometry by Xiaoqin Xu; Huanghao Yang; Ling Wang; Bin Han; Xiaoru Wang; Frank Sen-Chun Lee (pp. 87-96).
A solid-phase microextraction (SPME) method has been developed for the determination of 3 chloroacetanilide herbicides in both fresh and seawater samples. The extracted sample was analyzed by gas chromatography with mass spectrometry detection (GC–MS), and parameters affecting SPME operation including fibre type, sample pH, sample temperature, mixing speed and extraction time have been evaluated and optimized. The amount of dissolved organic matter (DOM) and the salt content both affected SPME extraction efficiency, but the presence of other competitive extractants such as organochlorine pesticides (OCPs) in the matrix showed no insignificance interference. The limit of detection (LOD) for acetochlor, metolachlor and butachlor were 1.2, 1.6 and 2.7ngL−1, respectively. The recoveries for the herbicides ranged from 79 to 102%, and the linear dynamic range was from 10 to 1000ngL−1. The developed method has been used to monitor herbicides contaminations in coastal water samples collected around Laizhou bay and Jiaozhou bay in Shandong peninsula, China. The concentrations of acetochlor and metolachlor ranged from undetectable to 78.5ngL−1 and undetectable to 35.6ngL−1, respectively. Butachlor was not observed but in only one sample and the concentration is lower than the limit of quantification (LOQ). The concentrations of the three herbicides in this study are low compared to most of the other places reported.
Keywords: Water analysis; Solid-phase microextraction; Environmental analysis; Herbicides; Gas chromatography–mass spectrometry
Chemical composition of contemporary black printing inks based on infrared spectroscopy: Basic information for the characterization and discrimination of artistic prints by Anna Vila; Núria Ferrer; Jose F. García (pp. 97-105).
This article aims to provide the basic information necessary to afford the discrimination of artistic prints based on chemical information. The presence of original and non-original prints in the art market is a real problem, especially for contemporary artists. Most of the non-original elements can be distinguished on the basis of their stylistics and printing characteristics, but sometimes this information is not enough. To facilitate discrimination in these cases, we propose to add, to the previously indicated aspects, the chemical information of the materials involved in the production of the original series (inks, paper and pencil). Comparison of the composition of any element with that established for the original series will permit the attribution of any doubtful element. This article is focused on the evaluation of this approach by determining the chemical composition of contemporary black printing inks by infrared spectroscopy and by searching, on the basis of the information obtained, for criteria capable to discriminate between prints made of different inks. The success of the approach with this set of inks could easily be extended to the study of colour inks. The study also includes the characterization and discrimination of black pigments because they are the most characteristic component of these inks and because this information can also be useful for other artistic studies. The procedure proposed permits the analysis of inks with minimum deterioration of the artwork. Results indicate the capability of the approach because, following the procedure, it is possible to distinguish between black pigments attending to the presence of hydroxyapatite, silicate and some other specific bands, whereas black inks can be discriminated by paying attention to the inclusion in their composition of such pigments as bone black, Prussian blue, mars brown or other specific bands. Scanning electron microscopy analyses have corroborated the results obtained.
Keywords: Artistic prints; Black pigments; Black inks; Characterization of artistic prints; Print discrimination; Fraud; Fake; Falsification; Infrared spectroscopy
Chemical composition of contemporary black printing inks based on infrared spectroscopy: Basic information for the characterization and discrimination of artistic prints by Anna Vila; Núria Ferrer; Jose F. García (pp. 97-105).
This article aims to provide the basic information necessary to afford the discrimination of artistic prints based on chemical information. The presence of original and non-original prints in the art market is a real problem, especially for contemporary artists. Most of the non-original elements can be distinguished on the basis of their stylistics and printing characteristics, but sometimes this information is not enough. To facilitate discrimination in these cases, we propose to add, to the previously indicated aspects, the chemical information of the materials involved in the production of the original series (inks, paper and pencil). Comparison of the composition of any element with that established for the original series will permit the attribution of any doubtful element. This article is focused on the evaluation of this approach by determining the chemical composition of contemporary black printing inks by infrared spectroscopy and by searching, on the basis of the information obtained, for criteria capable to discriminate between prints made of different inks. The success of the approach with this set of inks could easily be extended to the study of colour inks. The study also includes the characterization and discrimination of black pigments because they are the most characteristic component of these inks and because this information can also be useful for other artistic studies. The procedure proposed permits the analysis of inks with minimum deterioration of the artwork. Results indicate the capability of the approach because, following the procedure, it is possible to distinguish between black pigments attending to the presence of hydroxyapatite, silicate and some other specific bands, whereas black inks can be discriminated by paying attention to the inclusion in their composition of such pigments as bone black, Prussian blue, mars brown or other specific bands. Scanning electron microscopy analyses have corroborated the results obtained.
Keywords: Artistic prints; Black pigments; Black inks; Characterization of artistic prints; Print discrimination; Fraud; Fake; Falsification; Infrared spectroscopy
Chemiluminescent studies on the antioxidant activity of amino acids by T.M. Triantis; E. Yannakopoulou; A. Nikokavoura; D. Dimotikali; K. Papadopoulos (pp. 106-111).
The effect of various concentrations of essential α-amino acids on the luminol–sodium hypochlorite chemiluminescence (CL) has been studied. It was found that all tested compounds have an inhibiting effect. Amino acids with phenolic groups present higher inhibition than basic, acidic or neutral amino acids. The calculated antioxidant activities by the CL method are compared with those of the N, N-diphenyl-picryl hydrazyl (DPPH) method.
Keywords: Chemiluminescence; Antioxidant activity; Amino acids; N; ,; N; -Diphenyl-picryl hydrazyl (DPPH)
Chemiluminescent studies on the antioxidant activity of amino acids by T.M. Triantis; E. Yannakopoulou; A. Nikokavoura; D. Dimotikali; K. Papadopoulos (pp. 106-111).
The effect of various concentrations of essential α-amino acids on the luminol–sodium hypochlorite chemiluminescence (CL) has been studied. It was found that all tested compounds have an inhibiting effect. Amino acids with phenolic groups present higher inhibition than basic, acidic or neutral amino acids. The calculated antioxidant activities by the CL method are compared with those of the N, N-diphenyl-picryl hydrazyl (DPPH) method.
Keywords: Chemiluminescence; Antioxidant activity; Amino acids; N; ,; N; -Diphenyl-picryl hydrazyl (DPPH)
A rapid fluorimetric screening method for the 1,4-benzodiazepines: Determination of their metabolite oxazepam in urine by A.M. Gil Tejedor; P. Fernández Hernando; J.S. Durand Alegría (pp. 112-115).
Oxazepam is the major metabolite screened in urine samples for the evidence of the use of benzodiazepine drugs. The methods currently used, however, are laborious and time consuming. This paper proposes an oxazepam detection method based on its hydrolysis and cyclization – a reaction catalysed by cerium (IV) in an ortho-phosphoric acid-containing medium – to form 2-chloro-9(10H)-acridinone, a strongly fluorescent molecule. The variables involved in the hydrolysis and cyclization stages were optimised. Oxazepam was detectable in the 5–900ngmL−1 range, with a detection limit of 4.15ngmL−1 for k=3. The method was successfully used for the determination of oxazepam in urine samples collected at different times after the oral administration of Valium® and Tranxilium®.
Keywords: Benzodiazepines; Screening; Fluorimetry; Oxazepam; Urine
A rapid fluorimetric screening method for the 1,4-benzodiazepines: Determination of their metabolite oxazepam in urine by A.M. Gil Tejedor; P. Fernández Hernando; J.S. Durand Alegría (pp. 112-115).
Oxazepam is the major metabolite screened in urine samples for the evidence of the use of benzodiazepine drugs. The methods currently used, however, are laborious and time consuming. This paper proposes an oxazepam detection method based on its hydrolysis and cyclization – a reaction catalysed by cerium (IV) in an ortho-phosphoric acid-containing medium – to form 2-chloro-9(10H)-acridinone, a strongly fluorescent molecule. The variables involved in the hydrolysis and cyclization stages were optimised. Oxazepam was detectable in the 5–900ngmL−1 range, with a detection limit of 4.15ngmL−1 for k=3. The method was successfully used for the determination of oxazepam in urine samples collected at different times after the oral administration of Valium® and Tranxilium®.
Keywords: Benzodiazepines; Screening; Fluorimetry; Oxazepam; Urine
Sensitive determination of ultra-trace nitric oxide in blood using derivatization-polymer monolith microextraction coupled with reversed-phase high-performance liquid chromatography by Ke-Jing Huang; Min Zhang; Wan-Zhen Xie; Hua-Shan Zhang; Yu-Qi Feng; Hong Wang (pp. 116-122).
Nitric oxide (NO) plays a very important role in human blood system. In this work, a novel approach has been developed for the quantitation of ultra-trace NO derivatized with 1,3,5,7-tetramethyl-8-(3′,4′-diaminophenyl)-difluoroboradiaza- s- indacene (DAMBO) using a polymer monolith microextraction (PMME) with a poly(methacrylic acid-ethylene glycol dimethacrylate) (MAA-EGDMA) monolith in conjunction with high-performance liquid chromatography (HPLC). Both derivatization and PMME conditions have been optimized in detail. The detection limit of derivatized NO was 2×10−12molL−1 (signal to noise=3) and linear range was 9×10−11–4.5×10−8molL−1. The proposed DAMBO-based derivatization-PMME–HPLC-fluorescence detection method has been successfully applied for the determination of NO in 10μL blood samples of healthy persons and patients suffering from ischemic cardio-cerebrovascular diseases with recoveries varying from 87.40 to 91.60%.
Keywords: 1,3,5,7-Tetramethyl-8-(3′,4′-diaminophenyl)-difluoroboradiaza; -s; -indacene; Nitric oxide; Polymer monolith microextraction; Monolithic capillary column; Reversed-phase high-performance liquid chromatography
Sensitive determination of ultra-trace nitric oxide in blood using derivatization-polymer monolith microextraction coupled with reversed-phase high-performance liquid chromatography by Ke-Jing Huang; Min Zhang; Wan-Zhen Xie; Hua-Shan Zhang; Yu-Qi Feng; Hong Wang (pp. 116-122).
Nitric oxide (NO) plays a very important role in human blood system. In this work, a novel approach has been developed for the quantitation of ultra-trace NO derivatized with 1,3,5,7-tetramethyl-8-(3′,4′-diaminophenyl)-difluoroboradiaza- s- indacene (DAMBO) using a polymer monolith microextraction (PMME) with a poly(methacrylic acid-ethylene glycol dimethacrylate) (MAA-EGDMA) monolith in conjunction with high-performance liquid chromatography (HPLC). Both derivatization and PMME conditions have been optimized in detail. The detection limit of derivatized NO was 2×10−12molL−1 (signal to noise=3) and linear range was 9×10−11–4.5×10−8molL−1. The proposed DAMBO-based derivatization-PMME–HPLC-fluorescence detection method has been successfully applied for the determination of NO in 10μL blood samples of healthy persons and patients suffering from ischemic cardio-cerebrovascular diseases with recoveries varying from 87.40 to 91.60%.
Keywords: 1,3,5,7-Tetramethyl-8-(3′,4′-diaminophenyl)-difluoroboradiaza; -s; -indacene; Nitric oxide; Polymer monolith microextraction; Monolithic capillary column; Reversed-phase high-performance liquid chromatography
Process monitored spectrophotometric titration coupled with chemometrics for simultaneous determination of mixtures of weak acids by Lifu Liao; Jing Yang; Jintao Yuan (pp. 123-131).
A new spectrophotometric titration method coupled with chemometrics for the simultaneous determination of mixtures of weak acids has been developed. In this method, the titrant is a mixture of sodium hydroxide and an acid–base indicator, and the indicator is used to monitor the titration process. In a process of titration, both the added volume of titrant and the solution acidity at each titration point can be obtained simultaneously from an absorption spectrum by least square algorithm, and then the concentration of each component in the mixture can be obtained from the titration curves by principal component regression. The method only needs the information of absorbance spectra to obtain the analytical results, and is free of volumetric measurements. The analyses are independent of titration end point and do not need the accurate values of dissociation constants of the indicator and the acids. The method has been applied to the simultaneous determination of the mixtures of benzoic acid and salicylic acid, and the mixtures of phenol, o-chlorophenol and p-chlorophenol with satisfactory results.
Keywords: Spectrophotometric titration; Mixture of weak acids; Principal component regression
Process monitored spectrophotometric titration coupled with chemometrics for simultaneous determination of mixtures of weak acids by Lifu Liao; Jing Yang; Jintao Yuan (pp. 123-131).
A new spectrophotometric titration method coupled with chemometrics for the simultaneous determination of mixtures of weak acids has been developed. In this method, the titrant is a mixture of sodium hydroxide and an acid–base indicator, and the indicator is used to monitor the titration process. In a process of titration, both the added volume of titrant and the solution acidity at each titration point can be obtained simultaneously from an absorption spectrum by least square algorithm, and then the concentration of each component in the mixture can be obtained from the titration curves by principal component regression. The method only needs the information of absorbance spectra to obtain the analytical results, and is free of volumetric measurements. The analyses are independent of titration end point and do not need the accurate values of dissociation constants of the indicator and the acids. The method has been applied to the simultaneous determination of the mixtures of benzoic acid and salicylic acid, and the mixtures of phenol, o-chlorophenol and p-chlorophenol with satisfactory results.
Keywords: Spectrophotometric titration; Mixture of weak acids; Principal component regression
Simplified Fourier-transform mid-infrared spectroscopy calibration based on a spectra library for the on-line monitoring of bioprocesses by Jonas Schenk; Ian W. Marison; Urs von Stockar (pp. 132-140).
In order to significantly reduce the time involved in mid-infrared spectroscopy calibrations, a novel approach based on a library of pure component spectra was developed and tested with an aerobic Saccharomyces cerevisiae fermentation. Instead of the 30–50 standards that would have been required to build a chemometric model, only five solutions were used to assemble the library, namely one for each compound (glucose, ethanol, glycerol, ammonium and acetate). Concentration profiles of glucose, ethanol and ammonium were monitored with a fair accuracy, leading to standard error of prediction (SEP) values of 0.86, 0.98 and 0.15gL−1. Prediction of the two minor metabolites, acetate and glycerol, was less accurate and presented a detection limit of around 0.5gL−1. The overall performance of the library-based method proved to be very similar to a 49-standard chemometrics model. The model was shown to be very robust and uncorrelated, since it was able to predict accurately the concentration changes during a spiking experiment. Even though simple, this method allows more advanced calculations, such as determination of the explained variance and detection of unexpected compounds using residuals analysis.
Keywords: Mid-infrared spectroscopy; On-line monitoring; Bioprocess; Saccharomyces cerevisiae; Least squares modeling
Simplified Fourier-transform mid-infrared spectroscopy calibration based on a spectra library for the on-line monitoring of bioprocesses by Jonas Schenk; Ian W. Marison; Urs von Stockar (pp. 132-140).
In order to significantly reduce the time involved in mid-infrared spectroscopy calibrations, a novel approach based on a library of pure component spectra was developed and tested with an aerobic Saccharomyces cerevisiae fermentation. Instead of the 30–50 standards that would have been required to build a chemometric model, only five solutions were used to assemble the library, namely one for each compound (glucose, ethanol, glycerol, ammonium and acetate). Concentration profiles of glucose, ethanol and ammonium were monitored with a fair accuracy, leading to standard error of prediction (SEP) values of 0.86, 0.98 and 0.15gL−1. Prediction of the two minor metabolites, acetate and glycerol, was less accurate and presented a detection limit of around 0.5gL−1. The overall performance of the library-based method proved to be very similar to a 49-standard chemometrics model. The model was shown to be very robust and uncorrelated, since it was able to predict accurately the concentration changes during a spiking experiment. Even though simple, this method allows more advanced calculations, such as determination of the explained variance and detection of unexpected compounds using residuals analysis.
Keywords: Mid-infrared spectroscopy; On-line monitoring; Bioprocess; Saccharomyces cerevisiae; Least squares modeling