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Analytica Chimica Acta (v.575, #1)
Local factor analysis of rank-deficient reaction systems by C.J. Xu; S. Gourvénec; Y.Z. Liang; D.L. Massart (pp. 1-8).
The analysis of spectral measurement data sets using local factor analysis (LFA) requires the rank of the sub-matrix under study to be equal to the number of absorbing species present in the associated sub-system. However, because of mass balance or kinetic constraints, LFA will fail if local rank deficiency occurs. A local rank deficiency sub-system may be present in a global full-rank reaction system or a rank-deficient one. In this paper, the problems occurring when using window target-testing factor analysis (WTTFA), one type of the LFA methods, in a local rank-deficient situation are shown. A new augmented WTTFA (AWTTFA) is then proposed for the correct use of WTTFA when rank deficiency occurs. Principles of this new method have been demonstrated by a simulated kinetic system and an industrial batch data set.
Keywords: Local factor analysis (LFA); Window target-testing factor analysis (WTTFA); Rank deficiency; Local rank deficiency
Local factor analysis of rank-deficient reaction systems by C.J. Xu; S. Gourvénec; Y.Z. Liang; D.L. Massart (pp. 1-8).
The analysis of spectral measurement data sets using local factor analysis (LFA) requires the rank of the sub-matrix under study to be equal to the number of absorbing species present in the associated sub-system. However, because of mass balance or kinetic constraints, LFA will fail if local rank deficiency occurs. A local rank deficiency sub-system may be present in a global full-rank reaction system or a rank-deficient one. In this paper, the problems occurring when using window target-testing factor analysis (WTTFA), one type of the LFA methods, in a local rank-deficient situation are shown. A new augmented WTTFA (AWTTFA) is then proposed for the correct use of WTTFA when rank deficiency occurs. Principles of this new method have been demonstrated by a simulated kinetic system and an industrial batch data set.
Keywords: Local factor analysis (LFA); Window target-testing factor analysis (WTTFA); Rank deficiency; Local rank deficiency
Antimicrobial peptide-based array for Escherichia coli and Salmonella screening by Nadezhda V. Kulagina; Kara M. Shaffer; George P. Anderson; Frances S. Ligler; Chris R. Taitt (pp. 9-15).
Numerous bacteria, plants, and higher organisms produce antimicrobial peptides (AMPs) as part of their innate immune system, providing a chemical defense mechanism against microbial invasion. Many AMPs exert their antimicrobial activity by binding to components of the microbe's surface and disrupting the membrane. The goal of this study was to incorporate AMPs into screening assays for detection of pathogenic species. Surface-immobilized AMPs such as polymyxins B and E could be used to detect Salmonella typhimurium and Escherichia coli O157:H7 in two assay formats: direct and sandwich. Both types of assay confirmed that the peptides were immobilized in active form and could bind cells in a concentration-dependent manner. Cell binding to the AMPs was peptide-density dependent. This method for monitoring pathogen binding was extended to include other cationic AMPs such as cecropin A, magainin I and parasin. Detection limits (LODs) for E. coli O157:H7 and S. typhimurium obtained with AMPs during sandwich assays were in the ranges of 5×104 to 5×105 and 1×105 to 5×106cellsmL−1, respectively. The different AMPs showed significantly different affinities for the two bacterial species; the potential for classification of pathogens based on different binding patterns to AMPs is discussed.
Keywords: Antimicrobial peptides; Salmonella; Escherichia coli; Pathogen; Screening
Antimicrobial peptide-based array for Escherichia coli and Salmonella screening by Nadezhda V. Kulagina; Kara M. Shaffer; George P. Anderson; Frances S. Ligler; Chris R. Taitt (pp. 9-15).
Numerous bacteria, plants, and higher organisms produce antimicrobial peptides (AMPs) as part of their innate immune system, providing a chemical defense mechanism against microbial invasion. Many AMPs exert their antimicrobial activity by binding to components of the microbe's surface and disrupting the membrane. The goal of this study was to incorporate AMPs into screening assays for detection of pathogenic species. Surface-immobilized AMPs such as polymyxins B and E could be used to detect Salmonella typhimurium and Escherichia coli O157:H7 in two assay formats: direct and sandwich. Both types of assay confirmed that the peptides were immobilized in active form and could bind cells in a concentration-dependent manner. Cell binding to the AMPs was peptide-density dependent. This method for monitoring pathogen binding was extended to include other cationic AMPs such as cecropin A, magainin I and parasin. Detection limits (LODs) for E. coli O157:H7 and S. typhimurium obtained with AMPs during sandwich assays were in the ranges of 5×104 to 5×105 and 1×105 to 5×106cellsmL−1, respectively. The different AMPs showed significantly different affinities for the two bacterial species; the potential for classification of pathogens based on different binding patterns to AMPs is discussed.
Keywords: Antimicrobial peptides; Salmonella; Escherichia coli; Pathogen; Screening
Gold nanoelectrode ensembles for direct trace electroanalysis of iodide by Francisco C. Pereira; Ligia M. Moretto; Manuela De Leo; Maria V. Boldrin Zanoni; Paolo Ugo (pp. 16-24).
A procedure for the standardization of ensembles of gold nanodisk electrodes (NEE) of 30nm diameter is presented, which is based on the analytical comparison between experimental cyclic voltammograms (CV) obtained at the NEEs in diluted solutions of redox probes and CV patterns obtained by digital simulation. Possible origins of defects sometimes found in NEEs are discussed. Selected NEEs are then employed for the study of the electrochemical oxidation of iodide in acidic solutions. CV patterns display typical quasi-reversible behavior which involves associated chemical reactions between adsorbed and solution species. The main CV characteristics at the NEE compare with those observed at millimeter sized gold disk electrodes (Au-macro), apart a slight shift in E1/2 values and slightly higher peak to peak separation at the NEE. The detection limit (DL) at NEEs is 0.3μM, which is more than one order of magnitude lower than DL at the Au-macro (4μM). The mechanism of the electrochemical oxidation of iodide at NEEs is discussed. Finally, NEEs are applied to the direct determination of iodide at micromolar concentration levels in real samples, namely in some ophthalmic drugs and iodized table salt.
Keywords: Nanoelectrode ensembles; Iodide; Voltammetry; Edible salt; Ophthalmic drugs
Gold nanoelectrode ensembles for direct trace electroanalysis of iodide by Francisco C. Pereira; Ligia M. Moretto; Manuela De Leo; Maria V. Boldrin Zanoni; Paolo Ugo (pp. 16-24).
A procedure for the standardization of ensembles of gold nanodisk electrodes (NEE) of 30nm diameter is presented, which is based on the analytical comparison between experimental cyclic voltammograms (CV) obtained at the NEEs in diluted solutions of redox probes and CV patterns obtained by digital simulation. Possible origins of defects sometimes found in NEEs are discussed. Selected NEEs are then employed for the study of the electrochemical oxidation of iodide in acidic solutions. CV patterns display typical quasi-reversible behavior which involves associated chemical reactions between adsorbed and solution species. The main CV characteristics at the NEE compare with those observed at millimeter sized gold disk electrodes (Au-macro), apart a slight shift in E1/2 values and slightly higher peak to peak separation at the NEE. The detection limit (DL) at NEEs is 0.3μM, which is more than one order of magnitude lower than DL at the Au-macro (4μM). The mechanism of the electrochemical oxidation of iodide at NEEs is discussed. Finally, NEEs are applied to the direct determination of iodide at micromolar concentration levels in real samples, namely in some ophthalmic drugs and iodized table salt.
Keywords: Nanoelectrode ensembles; Iodide; Voltammetry; Edible salt; Ophthalmic drugs
Selective electrochemical sensor for copper (II) ion based on chelating ionophores by Ashok Kumar Singh; Sameena Mehtab; Ajay Kumar Jain (pp. 25-31).
Plasticized membranes using 3-(2-pyridinyl)-2H-pyrido[1,2,-a]-1,3,5-triazine-2,4(3H)-dithione (L1) and acetoacetanilide (L2) have been prepared and explored as Cu2+-selective sensors. Effect of various plasticizers, viz. chloronaphthalene (CN), benzyl acetate (BA), o-nitrophenyloctyl ether ( o-NPOE), and anion excluders, sodium tetraphenylborate (NaTPB) and oleic acid (OA) was studied in detail and improved performance was observed at several instances. Optimum performance was observed with dithione derivative (L1) having a membrane composition ofL1 (5):PVC (120): o-NPOE (240):OA (10). The sensor works satisfactorily in the concentration range 5.0×10−8 to 1.0×10−2M (detection limit 4.0×10−8M) with a Nernstian slope of 29.5mVdecade−1 of activity. Wide pH range (3.0–9.5), fast response time (12s), non-aqueous tolerance (up to 20%) and adequate shelf life (4 months) indicate the vital utility of the proposed sensor. The potentiometric selectivity coefficient values as determined by match potential method (MPM) indicate good response for Cu2+ in presence of interfering ions. The proposed electrode comparatively shows good selectivity with respect to alkali, alkaline earth, transition and some rare earth metals ions. The electrode was used for the determination of copper in different milk powder, water samples and as indicator electrode in potentiometric titration of copper ion with EDTA.
Keywords: Chelating ionophore; Poly(vinylchloride) membranes; Copper-selective electrode; Electrochemical sensors; Selectivity
Selective electrochemical sensor for copper (II) ion based on chelating ionophores by Ashok Kumar Singh; Sameena Mehtab; Ajay Kumar Jain (pp. 25-31).
Plasticized membranes using 3-(2-pyridinyl)-2H-pyrido[1,2,-a]-1,3,5-triazine-2,4(3H)-dithione (L1) and acetoacetanilide (L2) have been prepared and explored as Cu2+-selective sensors. Effect of various plasticizers, viz. chloronaphthalene (CN), benzyl acetate (BA), o-nitrophenyloctyl ether ( o-NPOE), and anion excluders, sodium tetraphenylborate (NaTPB) and oleic acid (OA) was studied in detail and improved performance was observed at several instances. Optimum performance was observed with dithione derivative (L1) having a membrane composition ofL1 (5):PVC (120): o-NPOE (240):OA (10). The sensor works satisfactorily in the concentration range 5.0×10−8 to 1.0×10−2M (detection limit 4.0×10−8M) with a Nernstian slope of 29.5mVdecade−1 of activity. Wide pH range (3.0–9.5), fast response time (12s), non-aqueous tolerance (up to 20%) and adequate shelf life (4 months) indicate the vital utility of the proposed sensor. The potentiometric selectivity coefficient values as determined by match potential method (MPM) indicate good response for Cu2+ in presence of interfering ions. The proposed electrode comparatively shows good selectivity with respect to alkali, alkaline earth, transition and some rare earth metals ions. The electrode was used for the determination of copper in different milk powder, water samples and as indicator electrode in potentiometric titration of copper ion with EDTA.
Keywords: Chelating ionophore; Poly(vinylchloride) membranes; Copper-selective electrode; Electrochemical sensors; Selectivity
Fabrication of a new polyaniline grafted multi-wall carbon nanotube modified electrode and its application for electrochemical detection of hydrogen peroxide by P. Santhosh; K.M. Manesh; A. Gopalan; Kwang-Pill Lee (pp. 32-38).
A modified electrode is fabricated by grafting polyaniline (PANI) chains onto multiwalled carbon nanotube (MWNT) for the detection of hydrogen peroxide (H2O2). PANI grafted MWNT modified electrode (PANI- g-MWNT-ME) displays excellent electrocatalytic response to the detection of H2O2 in a concentration range of (1.0–20)×10−8M showing linear response to current, with an extended lower detection limit down to 1nM. This modified electrode exhibits an accelerated electron transfer at the interface with minimized surface fouling and surface renewability. Further, electrochemical analysis of H2O2 performed in the presence of common interferents such as uric acid, ascorbic acid and acetaminophen with the modified electrode reveals that there is no overlapping signal from the interferents. The combined presence of MWNT and PANI in the modified electrode provides high sensitivity and selectivity.
Keywords: Multiwall carbon nanotube; Grafting; Modified electrode
Fabrication of a new polyaniline grafted multi-wall carbon nanotube modified electrode and its application for electrochemical detection of hydrogen peroxide by P. Santhosh; K.M. Manesh; A. Gopalan; Kwang-Pill Lee (pp. 32-38).
A modified electrode is fabricated by grafting polyaniline (PANI) chains onto multiwalled carbon nanotube (MWNT) for the detection of hydrogen peroxide (H2O2). PANI grafted MWNT modified electrode (PANI- g-MWNT-ME) displays excellent electrocatalytic response to the detection of H2O2 in a concentration range of (1.0–20)×10−8M showing linear response to current, with an extended lower detection limit down to 1nM. This modified electrode exhibits an accelerated electron transfer at the interface with minimized surface fouling and surface renewability. Further, electrochemical analysis of H2O2 performed in the presence of common interferents such as uric acid, ascorbic acid and acetaminophen with the modified electrode reveals that there is no overlapping signal from the interferents. The combined presence of MWNT and PANI in the modified electrode provides high sensitivity and selectivity.
Keywords: Multiwall carbon nanotube; Grafting; Modified electrode
Enhancement of a conducting polymer-based biosensor using carbon nanotube-doped polyaniline by Xiliang Luo; Anthony J. Killard; Aoife Morrin; Malcolm R. Smyth (pp. 39-44).
A biosensor with improved performance was developed through the immobilization of horseradish peroxidase (HRP) onto electropolymerized polyaniline (PANI) films doped with carbon nanotubes (CNTs). The effects of electropolymerization cycle and CNT concentration on the response of the biosensor toward H2O2 were investigated. It was found that the application of CNTs in the biosensor system could increase the amount and stability of the immobilized enzyme, and greatly enhanced the biosensor response. Compared with the biosensor without CNTs, the proposed biosensor exhibited enhanced stability and approximately eight-fold sensitivity. A linear range from 0.2 to 19μM for the detection of H2O2 was observed for the proposed biosensor, with a detection limit of 68nM at a signal-to-noise ratio of 3 and a response time of less than 5s.
Keywords: Carbon nanotubes; Polyaniline; Biosensor; Horseradish peroxidase; Hydrogen peroxide
Enhancement of a conducting polymer-based biosensor using carbon nanotube-doped polyaniline by Xiliang Luo; Anthony J. Killard; Aoife Morrin; Malcolm R. Smyth (pp. 39-44).
A biosensor with improved performance was developed through the immobilization of horseradish peroxidase (HRP) onto electropolymerized polyaniline (PANI) films doped with carbon nanotubes (CNTs). The effects of electropolymerization cycle and CNT concentration on the response of the biosensor toward H2O2 were investigated. It was found that the application of CNTs in the biosensor system could increase the amount and stability of the immobilized enzyme, and greatly enhanced the biosensor response. Compared with the biosensor without CNTs, the proposed biosensor exhibited enhanced stability and approximately eight-fold sensitivity. A linear range from 0.2 to 19μM for the detection of H2O2 was observed for the proposed biosensor, with a detection limit of 68nM at a signal-to-noise ratio of 3 and a response time of less than 5s.
Keywords: Carbon nanotubes; Polyaniline; Biosensor; Horseradish peroxidase; Hydrogen peroxide
Effect of condensation phenomena on potentiometric measurements by M.J. Guiomar H.M. Lito; M. Filomena Camões; Catarina M. Viçoso (pp. 45-51).
Results of potentiometric analysis, namely those of pH measurements, depend on temperature control of the experimental setup, as it is expressed in the analytical law, the Nernst equation, starting from the primary level, where reference values are conventionally assigned to standard solutions, through the whole traceability chain, down to the service laboratory.Fundamental studies of pH standards, based on the measurement of the potential of an electrochemical cell without transference, known as Harned cell, containing a platinum–hydrogen electrode and a silver–silver chloride reference electrode, refer condensation phenomena on the portions of the cell walls which are not immersed in the thermostatic bath, as one of the major sources of error in the assessment of both the silver–silver chloride electrode standard potential and on pH values. In this work such effect, which is bound to happen due to significant temperature differences between the ambient air temperature and the water bath, has been quantified, presenting an original contribution to the improvement of the quality of potentiometric analysis results. This was possible due to the availability of a climatic cabin “WALKIN? with a temperature control of ±0.01°C, which permitted that temperature gradients were built between the thermostat water bath (controlled to ±0.005°C) where cells filled to about 2/3 full were immersed up to 90% of their height, and the surrounding environment.
Keywords: Evaporation–condensation-phenomena; Temperature dependence; Potentiometric cells; Precision and accuracy of potentials; Primary pH measurements
Effect of condensation phenomena on potentiometric measurements by M.J. Guiomar H.M. Lito; M. Filomena Camões; Catarina M. Viçoso (pp. 45-51).
Results of potentiometric analysis, namely those of pH measurements, depend on temperature control of the experimental setup, as it is expressed in the analytical law, the Nernst equation, starting from the primary level, where reference values are conventionally assigned to standard solutions, through the whole traceability chain, down to the service laboratory.Fundamental studies of pH standards, based on the measurement of the potential of an electrochemical cell without transference, known as Harned cell, containing a platinum–hydrogen electrode and a silver–silver chloride reference electrode, refer condensation phenomena on the portions of the cell walls which are not immersed in the thermostatic bath, as one of the major sources of error in the assessment of both the silver–silver chloride electrode standard potential and on pH values. In this work such effect, which is bound to happen due to significant temperature differences between the ambient air temperature and the water bath, has been quantified, presenting an original contribution to the improvement of the quality of potentiometric analysis results. This was possible due to the availability of a climatic cabin “WALKIN” with a temperature control of ±0.01°C, which permitted that temperature gradients were built between the thermostat water bath (controlled to ±0.005°C) where cells filled to about 2/3 full were immersed up to 90% of their height, and the surrounding environment.
Keywords: Evaporation–condensation-phenomena; Temperature dependence; Potentiometric cells; Precision and accuracy of potentials; Primary pH measurements
Electrogenerated chemiluminescence biosensor based on Ru(bpy)32+ and dehydrogenase immobilized in sol–gel/chitosan/poly(sodium 4-styrene sulfonate) composite material by Lihua Zhang; Zhiai Xu; Shaojun Dong (pp. 52-56).
A new electrogenerated chemiluminescence biosensor was fabricated by immobilizing ECL reagent Ru(bpy)32+ and alcohol dehydrogenase in sol–gel/chitosan/poly(sodium 4-styrene sulfonate) (PSS) organically modified composite material. The component PSS was used to immobilize ECL reagent Ru(bpy)32+ by ion-exchange, while the addition of chitosan was to prevent the cracking of conventional sol–gel-derived glasses and provide biocompatible microenvironment for alcohol dehydrogenase. Such biosensor combined enzymatic selectivity with the sensitivity of ECL detection for quantification of enzyme substrate and it was much simpler than previous double-layer design. The detection limit was 9.3×10−6M for alcohol (S/N=3) with a linear range from 2.79×10−5 to 5.78×10−2M. With ECL detection, the biosensor exhibited wide linear range, high sensitivity and good stability.
Keywords: Electrogenerated chemiluminescence (ECL); Biosensor; Ru(bpy); 3; 2+; Alcohol dehydrogenase; Sol–gel/chitosan/PSS
Electrogenerated chemiluminescence biosensor based on Ru(bpy)32+ and dehydrogenase immobilized in sol–gel/chitosan/poly(sodium 4-styrene sulfonate) composite material by Lihua Zhang; Zhiai Xu; Shaojun Dong (pp. 52-56).
A new electrogenerated chemiluminescence biosensor was fabricated by immobilizing ECL reagent Ru(bpy)32+ and alcohol dehydrogenase in sol–gel/chitosan/poly(sodium 4-styrene sulfonate) (PSS) organically modified composite material. The component PSS was used to immobilize ECL reagent Ru(bpy)32+ by ion-exchange, while the addition of chitosan was to prevent the cracking of conventional sol–gel-derived glasses and provide biocompatible microenvironment for alcohol dehydrogenase. Such biosensor combined enzymatic selectivity with the sensitivity of ECL detection for quantification of enzyme substrate and it was much simpler than previous double-layer design. The detection limit was 9.3×10−6M for alcohol (S/N=3) with a linear range from 2.79×10−5 to 5.78×10−2M. With ECL detection, the biosensor exhibited wide linear range, high sensitivity and good stability.
Keywords: Electrogenerated chemiluminescence (ECL); Biosensor; Ru(bpy); 3; 2+; Alcohol dehydrogenase; Sol–gel/chitosan/PSS
Simultaneous determination of psychotropic drugs in human urine by capillary electrophoresis with electrochemiluminescence detection by Jianguo Li; Fengjuan Zhao; Huangxian Ju (pp. 57-61).
Amitriptyline, doxepin and chlorpromazine are often used as psychotropic drugs in treatment of the various mental diseases, and are also partly excreted by kidney. This work developed a simple, selective and sensitive method for their simultaneous monitoring in human urine using capillary electrophoresis coupled with electrochemiluminescence (ECL) detection based on end-column ECL reaction of tris-(2,2′-bipyridyl)ruthenium(II) with aliphatic tertiary amino moieties. Acetone was used as an additive to the running buffer to obtain their absolute separation. Under optimized conditions the proposed method displayed a linear range from 5.0 to 800ngmL−1 for the three drugs with the correlation coefficients more than 0.995 ( n=8). Their limits of detection were 0.8ngmL−1 (3.6fg), 1.0ngmL−1 (4.5fg) and 1.5ngmL−1 (6.8fg) at a signal to noise ratio of 3, respectively. The relative standard deviations for five determinations of 20ngmL−1 amitriptyline, doxepin and chlorpromazine were 1.7%, 4.2% and 3.6%, respectively. For practical application an extract step with 90:10 heptane/ethyl acetate (v/v) was performed to eliminate the influence of ionic strength in sample. The recoveries of amitriptyline, doxepin and chlorpromazine at different levels in human urine were between 83% and 93%, which showed that the method was valuable in clinical and biochemical laboratories for monitoring amitriptyline, doxepin and chlorpromazine.
Keywords: Capillary electrophoresis; Electrochemiluminescence; Tris(2,2′-bipyridyl) ruthenium(II); Amitriptyline; Doxepin; Chlorpromazine; Simultaneous determination
Simultaneous determination of psychotropic drugs in human urine by capillary electrophoresis with electrochemiluminescence detection by Jianguo Li; Fengjuan Zhao; Huangxian Ju (pp. 57-61).
Amitriptyline, doxepin and chlorpromazine are often used as psychotropic drugs in treatment of the various mental diseases, and are also partly excreted by kidney. This work developed a simple, selective and sensitive method for their simultaneous monitoring in human urine using capillary electrophoresis coupled with electrochemiluminescence (ECL) detection based on end-column ECL reaction of tris-(2,2′-bipyridyl)ruthenium(II) with aliphatic tertiary amino moieties. Acetone was used as an additive to the running buffer to obtain their absolute separation. Under optimized conditions the proposed method displayed a linear range from 5.0 to 800ngmL−1 for the three drugs with the correlation coefficients more than 0.995 ( n=8). Their limits of detection were 0.8ngmL−1 (3.6fg), 1.0ngmL−1 (4.5fg) and 1.5ngmL−1 (6.8fg) at a signal to noise ratio of 3, respectively. The relative standard deviations for five determinations of 20ngmL−1 amitriptyline, doxepin and chlorpromazine were 1.7%, 4.2% and 3.6%, respectively. For practical application an extract step with 90:10 heptane/ethyl acetate (v/v) was performed to eliminate the influence of ionic strength in sample. The recoveries of amitriptyline, doxepin and chlorpromazine at different levels in human urine were between 83% and 93%, which showed that the method was valuable in clinical and biochemical laboratories for monitoring amitriptyline, doxepin and chlorpromazine.
Keywords: Capillary electrophoresis; Electrochemiluminescence; Tris(2,2′-bipyridyl) ruthenium(II); Amitriptyline; Doxepin; Chlorpromazine; Simultaneous determination
A new chemiluminescence probe for singlet oxygen based on tetrathiafulvalene-anthracene dyad capable of performing detection in water/alcohol solution by Xiaoping Zheng; Shuna Sun; Deqing Zhang; Huimin Ma; Daoben Zhu (pp. 62-67).
A new tetrathiafulvalene-anthracene dyad1 with two “tetraethylene glycol? units was synthesized and characterized. Strong chemiluminescence was observed upon reaction of dyad1 with singlet oxygen (1O2), and this reaction shows fairly good selectivity toward1O2 over other reactive oxygen species. Due to the introduction of two hydrophilic “tetraethylene glycol? units, the detection of1O2 with dyad1 can be performed in alcohol/water solution, which is relatively a mild medium when compared with water/tetrahydrofuran solution required by other tetrathiafulvalene-anthracene dyads. Dyad1 may have a wider use for detection of1O2 in biological systems.
Keywords: Chemiluminescence probe; Singlet oxygen; Tetrathiafulvalene-anthracene dyad
A new chemiluminescence probe for singlet oxygen based on tetrathiafulvalene-anthracene dyad capable of performing detection in water/alcohol solution by Xiaoping Zheng; Shuna Sun; Deqing Zhang; Huimin Ma; Daoben Zhu (pp. 62-67).
A new tetrathiafulvalene-anthracene dyad1 with two “tetraethylene glycol” units was synthesized and characterized. Strong chemiluminescence was observed upon reaction of dyad1 with singlet oxygen (1O2), and this reaction shows fairly good selectivity toward1O2 over other reactive oxygen species. Due to the introduction of two hydrophilic “tetraethylene glycol” units, the detection of1O2 with dyad1 can be performed in alcohol/water solution, which is relatively a mild medium when compared with water/tetrahydrofuran solution required by other tetrathiafulvalene-anthracene dyads. Dyad1 may have a wider use for detection of1O2 in biological systems.
Keywords: Chemiluminescence probe; Singlet oxygen; Tetrathiafulvalene-anthracene dyad
Spectrofluorimetric study of the interaction of copper(II) and bis-heterocyclictriazene reagent in the presence of β-cyclodextrin by Feng Feng; Xueming Liao; Zezhong Chen; Sen Lin; Shuangming Meng; Zhen Lu (pp. 68-75).
A new reagent, 1,3-bis(2-benzothiazolyl-diazoamino)benzene (BBTAB), was first synthesized and characterized by elemental analysis,1H NMR and IR spectra. The inclusion complex of BBTAB with β-cyclodextrin (β-CD) was formed. BBTAB in the inclusion complex or alone reacts with copper(II) to form chelate complex in a slight basic medium, which results in drastic or slight fluorescence enhancement, respectively. The spectrofluorimetric method of trace amount of copper(II) based on the enhancement of inclusion complex by binding with copper(II) was established. The excitation and emission wavelengths of the BBTAB/β-CD/Cu system are 389 and 480nm, respectively. Under optimal conditions, a linear response of BBTAB/β-CD to copper(II) is obtained in the range of 3.0×10−7 to 1.0×10−5molL−1, and the detection limit is determined to be 1.2×10−8molL−1. The method is selective, sensitive and simple, and has been used for the determination of trace copper(II) in water samples with satisfactory results. The possible response mechanism of BBTAB/β-CD or BBTAB to copper(II) and the role of β-CD in the drastic enhancement of fluorescence of BBTAB/β-CD/Cu system have been discussed.
Keywords: 1,3-Bis(2-benzothiazolyl-diazoamino)benzene; Fluorescence enhancement; Copper(II); β-Cyclodextrin
Spectrofluorimetric study of the interaction of copper(II) and bis-heterocyclictriazene reagent in the presence of β-cyclodextrin by Feng Feng; Xueming Liao; Zezhong Chen; Sen Lin; Shuangming Meng; Zhen Lu (pp. 68-75).
A new reagent, 1,3-bis(2-benzothiazolyl-diazoamino)benzene (BBTAB), was first synthesized and characterized by elemental analysis,1H NMR and IR spectra. The inclusion complex of BBTAB with β-cyclodextrin (β-CD) was formed. BBTAB in the inclusion complex or alone reacts with copper(II) to form chelate complex in a slight basic medium, which results in drastic or slight fluorescence enhancement, respectively. The spectrofluorimetric method of trace amount of copper(II) based on the enhancement of inclusion complex by binding with copper(II) was established. The excitation and emission wavelengths of the BBTAB/β-CD/Cu system are 389 and 480nm, respectively. Under optimal conditions, a linear response of BBTAB/β-CD to copper(II) is obtained in the range of 3.0×10−7 to 1.0×10−5molL−1, and the detection limit is determined to be 1.2×10−8molL−1. The method is selective, sensitive and simple, and has been used for the determination of trace copper(II) in water samples with satisfactory results. The possible response mechanism of BBTAB/β-CD or BBTAB to copper(II) and the role of β-CD in the drastic enhancement of fluorescence of BBTAB/β-CD/Cu system have been discussed.
Keywords: 1,3-Bis(2-benzothiazolyl-diazoamino)benzene; Fluorescence enhancement; Copper(II); β-Cyclodextrin
Atmospheric-pressure ionization studies and field dependence of ion mobilities of isomeric hydrocarbons using a miniature differential mobility spectrometer by H. Borsdorf; E.G. Nazarov; R.A. Miller (pp. 76-88).
The ionization pathways and ion mobility were determined for sets of structural isomeric and stereoisomeric non-polar hydrocarbons (saturated and unsaturated cyclic hydrocarbons and aromatic hydrocarbons) using a novel miniature differential mobility spectrometer with atmospheric-pressure photoionization (APPI) to assess how structural and stereochemical differences influence ion formation and ion mobility. The analytical results obtained using the differential mobility spectrometry (DMS) were compared with the reduced mobility values measured using conventional time-of-flight ion mobility spectrometry (IMS) with the same ionization technique.The majority of differences in DMS ion mobility spectra observed among isomeric cyclic hydrocarbons can be explained by the formation of different product ions. Comparable differences in ion formation were also observed using conventional IMS and by investigations using the coupling of ion mobility spectrometry with mass spectrometry (APPI-IMS-MS) and APPI-MS. Using DMS, isomeric aromatic hydrocarbons can in the majority of cases be distinguished by the different behavior of product ions in the strong asymmetric radio frequency (rf) electric field of the drift channel. The different peak position of product ions depending on the electric field amplitude permits the differentiation between most of the investigated isomeric aromatics with a different constitution; this stands in contrast to conventional IMS in which comparable reduced mobility values were detected for the isomeric aromatic compounds.
Keywords: Differential mobility spectrometry; Ion mobility spectrometry; Isomeric compounds
Atmospheric-pressure ionization studies and field dependence of ion mobilities of isomeric hydrocarbons using a miniature differential mobility spectrometer by H. Borsdorf; E.G. Nazarov; R.A. Miller (pp. 76-88).
The ionization pathways and ion mobility were determined for sets of structural isomeric and stereoisomeric non-polar hydrocarbons (saturated and unsaturated cyclic hydrocarbons and aromatic hydrocarbons) using a novel miniature differential mobility spectrometer with atmospheric-pressure photoionization (APPI) to assess how structural and stereochemical differences influence ion formation and ion mobility. The analytical results obtained using the differential mobility spectrometry (DMS) were compared with the reduced mobility values measured using conventional time-of-flight ion mobility spectrometry (IMS) with the same ionization technique.The majority of differences in DMS ion mobility spectra observed among isomeric cyclic hydrocarbons can be explained by the formation of different product ions. Comparable differences in ion formation were also observed using conventional IMS and by investigations using the coupling of ion mobility spectrometry with mass spectrometry (APPI-IMS-MS) and APPI-MS. Using DMS, isomeric aromatic hydrocarbons can in the majority of cases be distinguished by the different behavior of product ions in the strong asymmetric radio frequency (rf) electric field of the drift channel. The different peak position of product ions depending on the electric field amplitude permits the differentiation between most of the investigated isomeric aromatics with a different constitution; this stands in contrast to conventional IMS in which comparable reduced mobility values were detected for the isomeric aromatic compounds.
Keywords: Differential mobility spectrometry; Ion mobility spectrometry; Isomeric compounds
Simultaneous determination of phenyl- and sulfonyl-urea herbicides in river water at sub-parts-per-billion level by on-line preconcentration and liquid chromatography–tandem mass spectrometry by I. Losito; A. Amorisco; T. Carbonara; S. Lofiego; F. Palmisano (pp. 89-96).
A method based on on-line preconcentration followed by liquid chromatography-electrospray ionization–tandem mass spectrometry (LC-ESI–MS/MS) was developed for the determination of three sulfonyl-urea (thifensulfuron, metsulfuron, chlorsulfuron) and two phenyl-urea (isoproturon and chlortoluron) herbicides in water at sub-ppb concentration ranges.Preconcentration was accomplished using on-line enrichment on a C18 cartridge; the procedure was optimized by an evaluation of the breakthrough volumes for the target analytes. Subsequently, LC-ESI–MS/MS was adopted for analytes separation and detection.In particular, a selective reaction monitoring (SRM) approach, based on the detection of a peculiar fragment for each analyte, was chosen for MS/MS analysis, in order to enhance selectivity. Normalization to the response of a phenyl-urea herbicide (chloroxuron), used as an internal standard, was also adopted to achieve a reproducibility enhancement.The described method was applied to the analysis of the target analytes in river water samples and LOD values ranging between 8 and 30 ppt were obtained.
Keywords: Phenyl-urea herbicides; Sulfonyl-urea herbicides; On-line preconcentration; Liquid chromatography-electrospray ionization–mass spectrometry; Water analysis
Simultaneous determination of phenyl- and sulfonyl-urea herbicides in river water at sub-parts-per-billion level by on-line preconcentration and liquid chromatography–tandem mass spectrometry by I. Losito; A. Amorisco; T. Carbonara; S. Lofiego; F. Palmisano (pp. 89-96).
A method based on on-line preconcentration followed by liquid chromatography-electrospray ionization–tandem mass spectrometry (LC-ESI–MS/MS) was developed for the determination of three sulfonyl-urea (thifensulfuron, metsulfuron, chlorsulfuron) and two phenyl-urea (isoproturon and chlortoluron) herbicides in water at sub-ppb concentration ranges.Preconcentration was accomplished using on-line enrichment on a C18 cartridge; the procedure was optimized by an evaluation of the breakthrough volumes for the target analytes. Subsequently, LC-ESI–MS/MS was adopted for analytes separation and detection.In particular, a selective reaction monitoring (SRM) approach, based on the detection of a peculiar fragment for each analyte, was chosen for MS/MS analysis, in order to enhance selectivity. Normalization to the response of a phenyl-urea herbicide (chloroxuron), used as an internal standard, was also adopted to achieve a reproducibility enhancement.The described method was applied to the analysis of the target analytes in river water samples and LOD values ranging between 8 and 30 ppt were obtained.
Keywords: Phenyl-urea herbicides; Sulfonyl-urea herbicides; On-line preconcentration; Liquid chromatography-electrospray ionization–mass spectrometry; Water analysis
High-performance liquid chromatographic determination of biogenic amines in wines with an experimental design optimization procedure by Natividad García-Villar; Javier Saurina; Santiago Hernández-Cassou (pp. 97-105).
A novel and sensitive HPLC method for determining biogenic amines in wine samples is described. It involves pre-column labeling of the analytes with 1,2-naphthoquinone-4-sulfonate (NQS) and liquid–liquid extraction of derivatives with chloroform for analyte preconcentration and sample clean-up. A linear gradient elution consisting of a mixture of 2% of acetic acid aqueous solution and methanol is used to separate the amine derivatives in a C18 column. The eluted compounds are detected spectrophotometrically at 270nm. The optimization of both derivatization and separation conditions is accomplished by means of factorial and central composite designs and multicriteria decision functions. The analytical parameters of the method are established using red wine samples. Detection limits range from 0.006 to 0.315mgL−1. The run-to-run repeatabilities of retention times and peak areas are around 0.6 and 5.6%, respectively. Recoveries ranging from 91.9 to 105% prove the accuracy of the method for determining histamine, putrescine, cadaverine, tryptamine, phenylethylamine and serotonin in red wines. The proposed method has been applied to the analysis of commercial wines from different Spanish regions.
Keywords: Biogenic amines; Derivatization; High-performance liquid chromatography (HPLC); Experimental design; Wines
High-performance liquid chromatographic determination of biogenic amines in wines with an experimental design optimization procedure by Natividad García-Villar; Javier Saurina; Santiago Hernández-Cassou (pp. 97-105).
A novel and sensitive HPLC method for determining biogenic amines in wine samples is described. It involves pre-column labeling of the analytes with 1,2-naphthoquinone-4-sulfonate (NQS) and liquid–liquid extraction of derivatives with chloroform for analyte preconcentration and sample clean-up. A linear gradient elution consisting of a mixture of 2% of acetic acid aqueous solution and methanol is used to separate the amine derivatives in a C18 column. The eluted compounds are detected spectrophotometrically at 270nm. The optimization of both derivatization and separation conditions is accomplished by means of factorial and central composite designs and multicriteria decision functions. The analytical parameters of the method are established using red wine samples. Detection limits range from 0.006 to 0.315mgL−1. The run-to-run repeatabilities of retention times and peak areas are around 0.6 and 5.6%, respectively. Recoveries ranging from 91.9 to 105% prove the accuracy of the method for determining histamine, putrescine, cadaverine, tryptamine, phenylethylamine and serotonin in red wines. The proposed method has been applied to the analysis of commercial wines from different Spanish regions.
Keywords: Biogenic amines; Derivatization; High-performance liquid chromatography (HPLC); Experimental design; Wines
Formation of halogenated by-products of parabens in chlorinated water by P. Canosa; I. Rodríguez; E. Rubí; N. Negreira; R. Cela (pp. 106-113).
Chemical transformations of four alkyl esters of p-hydroxybenzoic acid, parabens, in chlorinated water samples are investigated. Quantification of the parent species and identification of their reaction by-products were performed using gas chromatography in combination with mass spectrometry. Experiments were accomplished considering free chlorine and paraben concentrations at the mgL−1 and μgL−1 level, respectively. Concentration of water samples, using solid-phase extraction, and silylation of the target species were carried out in order to improve the detectability of parent species and their possible transformation products, achieving quantification limits at the low ngL−1 level. Under employed experimental conditions, the decrease in the concentrations of parabens followed pseudo-first-order kinetics. Half-lives values obtained for model ultrapure water solutions were in good agreement with those observed in tap water samples. For the first type of sample, only two by-products were detected for each paraben. They corresponded to chlorination of the aromatic ring in one or two carbons situated in ortho-positions to the hydroxyl group. Both species were also generated after the addition of parabens to chlorinated tap water. Moreover, three new transformation products were noticed for each parent compound. They were identified as bromo- and bromochloro-parabens, formed due to the existence of traces of bromide in tap water sources. Experiments carried out by mixing paraben-containing personal care products with tap water, containing free chlorine, confirmed the formation of all above described halogenated by-products. In addition, the presence of the di-chlorinated forms of methyl and propyl paraben has been detected for first time in raw sewage water samples.
Keywords: Parabens; Chlorine; Halogenated by-products; Water samples; Gas chromatography–mass spectrometry
Formation of halogenated by-products of parabens in chlorinated water by P. Canosa; I. Rodríguez; E. Rubí; N. Negreira; R. Cela (pp. 106-113).
Chemical transformations of four alkyl esters of p-hydroxybenzoic acid, parabens, in chlorinated water samples are investigated. Quantification of the parent species and identification of their reaction by-products were performed using gas chromatography in combination with mass spectrometry. Experiments were accomplished considering free chlorine and paraben concentrations at the mgL−1 and μgL−1 level, respectively. Concentration of water samples, using solid-phase extraction, and silylation of the target species were carried out in order to improve the detectability of parent species and their possible transformation products, achieving quantification limits at the low ngL−1 level. Under employed experimental conditions, the decrease in the concentrations of parabens followed pseudo-first-order kinetics. Half-lives values obtained for model ultrapure water solutions were in good agreement with those observed in tap water samples. For the first type of sample, only two by-products were detected for each paraben. They corresponded to chlorination of the aromatic ring in one or two carbons situated in ortho-positions to the hydroxyl group. Both species were also generated after the addition of parabens to chlorinated tap water. Moreover, three new transformation products were noticed for each parent compound. They were identified as bromo- and bromochloro-parabens, formed due to the existence of traces of bromide in tap water sources. Experiments carried out by mixing paraben-containing personal care products with tap water, containing free chlorine, confirmed the formation of all above described halogenated by-products. In addition, the presence of the di-chlorinated forms of methyl and propyl paraben has been detected for first time in raw sewage water samples.
Keywords: Parabens; Chlorine; Halogenated by-products; Water samples; Gas chromatography–mass spectrometry
Microwave-assisted UV-digestion procedure for the accurate determination of Pd in natural waters by Andreas Limbeck (pp. 114-119).
A procedure was developed for the selective determination of Pd in environmental aquatic solutions. The method is based on a preliminary microwave-assisted UV-digestion for the degradation of dissolved organic material, and the subsequent determination of Pd using a recently presented enrichment procedure with ETAAS detection. Due to the simultaneous use of microwave and UV irradiation only extremely small quantities of hydrogen peroxide were necessary to yield a quantitative degradation of interfering organic ligands. Thus the on-line pre-concentration of Pd in the digested samples using the complexing agent N, N-diethyl- N′-benzoylthiourea was possible without any further sample pre-treatment. Using a sample volume of 1.57ml for FI-ETAAS analysis a limit of detection of 15ngl−1 was obtained for the combined procedure, with a relative standard deviation being not more than 4.9%. The method was applied to quantify the water-soluble fraction of Pd in urban road dust. Extractions with a rain sample of pH 5.9 revealed that an average of 2.2% ( n=8) of the total Pd present in urban road dust was water soluble.
Keywords: Palladium; On-line pre-concentration; Water solubility; UV-digestion
Microwave-assisted UV-digestion procedure for the accurate determination of Pd in natural waters by Andreas Limbeck (pp. 114-119).
A procedure was developed for the selective determination of Pd in environmental aquatic solutions. The method is based on a preliminary microwave-assisted UV-digestion for the degradation of dissolved organic material, and the subsequent determination of Pd using a recently presented enrichment procedure with ETAAS detection. Due to the simultaneous use of microwave and UV irradiation only extremely small quantities of hydrogen peroxide were necessary to yield a quantitative degradation of interfering organic ligands. Thus the on-line pre-concentration of Pd in the digested samples using the complexing agent N, N-diethyl- N′-benzoylthiourea was possible without any further sample pre-treatment. Using a sample volume of 1.57ml for FI-ETAAS analysis a limit of detection of 15ngl−1 was obtained for the combined procedure, with a relative standard deviation being not more than 4.9%. The method was applied to quantify the water-soluble fraction of Pd in urban road dust. Extractions with a rain sample of pH 5.9 revealed that an average of 2.2% ( n=8) of the total Pd present in urban road dust was water soluble.
Keywords: Palladium; On-line pre-concentration; Water solubility; UV-digestion
Development of microwave-assisted extraction followed by headspace solid-phase microextraction and gas chromatography–mass spectrometry for quantification of camphor and borneol in Flos Chrysanthemi Indici by Chunhui Deng; Yu Mao; Ning Yao; Xiangmin Zhang (pp. 120-125).
In the work, microwave-assisted extraction (MAE) followed by headspace solid-phase microextraction (HS-SPME) and gas chromatography–mass spectrometry (GC–MS) was developed for quantitative analysis of the bioactive components of camphor and borneol in a traditional Chinese medicines (TCM) of Flos Chrysanthemi Indici. After systematical investigation, the optimal experimental parameters microwave power (400W), irradiation time (4min), fiber coating (PDMS/DVB fiber), extraction temperature (40°C), extraction time (20min), stirring rate (1100rpm), and salt effect (no salt added) were investigated. The optimized method provided satisfactory precision (RSD values less than 12%), good recovery (from 86% to 94%), and good linearity ( R2>0.999). The proposed method was applied to quantitative analysis of camphor and borneol in Flos Chrysanthemi Indici samples from 11 different growing areas. To demonstrate the method feasibility, steam distillation was also used to analyze camphor and borneol in Flos Chrysanthemi Indici samples from these different growing areas. The very close results were obtained by the two methods. It has been shown that the proposed ME–HS-SPME–GC–MS is a simple, rapid, solvent-free and reliable method for quantitative analysis of camphor and borneol in TCM, and a potential tool for quality assessment of Flos Chrysanthemi Indici.
Keywords: Traditional Chinese medicines; Flos Chrysanthemi Indici; Microwave-assisted extraction; Headspace solid-phase microextraction; Active compounds; Quality assessment
Development of microwave-assisted extraction followed by headspace solid-phase microextraction and gas chromatography–mass spectrometry for quantification of camphor and borneol in Flos Chrysanthemi Indici by Chunhui Deng; Yu Mao; Ning Yao; Xiangmin Zhang (pp. 120-125).
In the work, microwave-assisted extraction (MAE) followed by headspace solid-phase microextraction (HS-SPME) and gas chromatography–mass spectrometry (GC–MS) was developed for quantitative analysis of the bioactive components of camphor and borneol in a traditional Chinese medicines (TCM) of Flos Chrysanthemi Indici. After systematical investigation, the optimal experimental parameters microwave power (400W), irradiation time (4min), fiber coating (PDMS/DVB fiber), extraction temperature (40°C), extraction time (20min), stirring rate (1100rpm), and salt effect (no salt added) were investigated. The optimized method provided satisfactory precision (RSD values less than 12%), good recovery (from 86% to 94%), and good linearity ( R2>0.999). The proposed method was applied to quantitative analysis of camphor and borneol in Flos Chrysanthemi Indici samples from 11 different growing areas. To demonstrate the method feasibility, steam distillation was also used to analyze camphor and borneol in Flos Chrysanthemi Indici samples from these different growing areas. The very close results were obtained by the two methods. It has been shown that the proposed ME–HS-SPME–GC–MS is a simple, rapid, solvent-free and reliable method for quantitative analysis of camphor and borneol in TCM, and a potential tool for quality assessment of Flos Chrysanthemi Indici.
Keywords: Traditional Chinese medicines; Flos Chrysanthemi Indici; Microwave-assisted extraction; Headspace solid-phase microextraction; Active compounds; Quality assessment
Evaluation of polychlorotrifluoroethylene as sorbent material for on-line solid phase extraction systems: Determination of copper and lead by flame atomic absorption spectrometry in water samples by Aristidis N. Anthemidis; Kallirroy-Ioanna G. Ioannou (pp. 126-132).
Polychlorotrifluoroethylene (PCTFE) in the form of beads was applied, as packing material for flow injection on-line column preconcentration and separation systems coupled with flame atomic absorption spectrometry (FAAS). Its performance characteristics were evaluated for trace copper determination in environmental samples. The on-line formed complex of metal with diethyldithiophosphate (DDPA) was sorbed on the PCTFE surface. Isobutyl methyl ketone (IBMK) at a flow rate of 2.8mLmin−1 was used to elute the analyte complex directly into the nebulizer–burner system of spectrophotometer. The proposed sorbent material reveal, excellent chemical and mechanical resistance, fast adsorption kinetics permitting the use of high sample flow rates up to 15mLmin−1 without loss of retention efficiency. For copper determination, with 90s preconcentration time the sample frequency was 30h−1, the enhancement factor was 250, which could be further improved by increasing the loading (preconcentration) time. The detection limit (3 s) was cL=0.07μgL−1, and the precision (R.S.D.) was 1.8%, at the 2.0μgL−1 Cu(II) level. For lead determination, the detection limit was cL=2.7μgL−1, and the precision (R.S.D.) 2.2%, at the 40.0μgL−1 Pb(II) level. The accuracy of the developed method was evaluated by analyzing certified reference materials and by recovery measurements on spiked natural water samples.
Keywords: Copper; Polychlorotrifluoroethylene; On-line preconcentration; Atomic absorption spectrometry
Evaluation of polychlorotrifluoroethylene as sorbent material for on-line solid phase extraction systems: Determination of copper and lead by flame atomic absorption spectrometry in water samples by Aristidis N. Anthemidis; Kallirroy-Ioanna G. Ioannou (pp. 126-132).
Polychlorotrifluoroethylene (PCTFE) in the form of beads was applied, as packing material for flow injection on-line column preconcentration and separation systems coupled with flame atomic absorption spectrometry (FAAS). Its performance characteristics were evaluated for trace copper determination in environmental samples. The on-line formed complex of metal with diethyldithiophosphate (DDPA) was sorbed on the PCTFE surface. Isobutyl methyl ketone (IBMK) at a flow rate of 2.8mLmin−1 was used to elute the analyte complex directly into the nebulizer–burner system of spectrophotometer. The proposed sorbent material reveal, excellent chemical and mechanical resistance, fast adsorption kinetics permitting the use of high sample flow rates up to 15mLmin−1 without loss of retention efficiency. For copper determination, with 90s preconcentration time the sample frequency was 30h−1, the enhancement factor was 250, which could be further improved by increasing the loading (preconcentration) time. The detection limit (3 s) was cL=0.07μgL−1, and the precision (R.S.D.) was 1.8%, at the 2.0μgL−1 Cu(II) level. For lead determination, the detection limit was cL=2.7μgL−1, and the precision (R.S.D.) 2.2%, at the 40.0μgL−1 Pb(II) level. The accuracy of the developed method was evaluated by analyzing certified reference materials and by recovery measurements on spiked natural water samples.
Keywords: Copper; Polychlorotrifluoroethylene; On-line preconcentration; Atomic absorption spectrometry
A pre-concentration procedure using coprecipitation for determination of lead and iron in several samples using flame atomic absorption spectrometry by S. Saracoglu; M. Soylak; D.S. Kacar Peker; L. Elci; W.N.L. dos Santos; V.A. Lemos; S.L.C. Ferreira (pp. 133-137).
The present paper proposes a pre-concentration procedure for determination of lead and iron in several samples by flame atomic absorption spectrometry. In it, lead(II) and iron(III) ions are coprecipitated using the violuric acid–copper(II) system as collector. Afterwards, the precipitate is dissolved with 1M HNO3 solution and the metal ions are determined. The optimization step was performed using factorial design involving the variables: pH, violuric acid mass (VA) and copper concentration (Cu).Using the optimized experimental conditions, the proposed procedure allows the determination these metals with detection limits of 0.18μgL−1 for iron and 0.16μgL−1 for lead. The effects of foreign ions on the pre-concentration procedure were also evaluated and the results demonstrated that this method could be applied for determination of iron and lead in several real samples. The proposed method was successfully applied to the analysis of seawater, urine, mineral water, soil and physiological solution samples. The concentrations of lead and iron achieved in these samples agree well with others data reported in the literature.
Keywords: Pre-concentration; Coprecipitation; Iron; Lead; Factorial design
A pre-concentration procedure using coprecipitation for determination of lead and iron in several samples using flame atomic absorption spectrometry by S. Saracoglu; M. Soylak; D.S. Kacar Peker; L. Elci; W.N.L. dos Santos; V.A. Lemos; S.L.C. Ferreira (pp. 133-137).
The present paper proposes a pre-concentration procedure for determination of lead and iron in several samples by flame atomic absorption spectrometry. In it, lead(II) and iron(III) ions are coprecipitated using the violuric acid–copper(II) system as collector. Afterwards, the precipitate is dissolved with 1M HNO3 solution and the metal ions are determined. The optimization step was performed using factorial design involving the variables: pH, violuric acid mass (VA) and copper concentration (Cu).Using the optimized experimental conditions, the proposed procedure allows the determination these metals with detection limits of 0.18μgL−1 for iron and 0.16μgL−1 for lead. The effects of foreign ions on the pre-concentration procedure were also evaluated and the results demonstrated that this method could be applied for determination of iron and lead in several real samples. The proposed method was successfully applied to the analysis of seawater, urine, mineral water, soil and physiological solution samples. The concentrations of lead and iron achieved in these samples agree well with others data reported in the literature.
Keywords: Pre-concentration; Coprecipitation; Iron; Lead; Factorial design
Application of liquid-phase microextraction to the analysis of trihalomethanes in water by Ali Tor; M. Emin Aydin (pp. 138-143).
A liquid-phase microextraction method for the determination of trihalomethanes (THMs) including chloroform (CHCl3), bromodichloromethane (CHBrCl2), dibromochloromethane (CHBr2Cl) and bromoform (CHBr3) in water samples was developed, with analysis by gas chromatography-electron capture detection (GC-ECD). After the determination of the most suitable solvent and stirring rate for the extraction, several other parameters (solvent drop volume, extraction time and ionic strength of the sample) were optimized using a factorial design to obtain the most relevant variables. The optimized extraction conditions for 5mL of sample volume in a 10mL vial were as follows: n-hexane an organic solvent; a solvent drop volume of 2μL; an extraction time of 5.0min; a stirring rate of 600rpm at 25°C; sample ionic strength of 3M sodium chloride. The linear range was 1–75μgL−1 for the studied THMs. The limits of detection (LODs) ranged from 0.23μgL−1 (for CHBr2Cl) to 0.45μgL−1 (for CHCl3). Recoveries of THMs from fortified distilled water were over 70% for a fortification level of 15μgL−1, and relative standard deviations of the recoveries were below 5%. Real samples collected from tap water and well water were successfully analyzed using the proposed method. The recovery of spiked water samples was from 73% to 78% with relative standard deviations below 7%.
Keywords: Trihalomethanes; Liquid-phase microextraction; Water analysis; Factorial design
Application of liquid-phase microextraction to the analysis of trihalomethanes in water by Ali Tor; M. Emin Aydin (pp. 138-143).
A liquid-phase microextraction method for the determination of trihalomethanes (THMs) including chloroform (CHCl3), bromodichloromethane (CHBrCl2), dibromochloromethane (CHBr2Cl) and bromoform (CHBr3) in water samples was developed, with analysis by gas chromatography-electron capture detection (GC-ECD). After the determination of the most suitable solvent and stirring rate for the extraction, several other parameters (solvent drop volume, extraction time and ionic strength of the sample) were optimized using a factorial design to obtain the most relevant variables. The optimized extraction conditions for 5mL of sample volume in a 10mL vial were as follows: n-hexane an organic solvent; a solvent drop volume of 2μL; an extraction time of 5.0min; a stirring rate of 600rpm at 25°C; sample ionic strength of 3M sodium chloride. The linear range was 1–75μgL−1 for the studied THMs. The limits of detection (LODs) ranged from 0.23μgL−1 (for CHBr2Cl) to 0.45μgL−1 (for CHCl3). Recoveries of THMs from fortified distilled water were over 70% for a fortification level of 15μgL−1, and relative standard deviations of the recoveries were below 5%. Real samples collected from tap water and well water were successfully analyzed using the proposed method. The recovery of spiked water samples was from 73% to 78% with relative standard deviations below 7%.
Keywords: Trihalomethanes; Liquid-phase microextraction; Water analysis; Factorial design
Analysis of charge transport in gels containing polyoxometallates using methods of different sensitivity to migration by Karolina Caban; Adam Lewera; Grazyna Z. Zukowska; Pawel J. Kulesza; Zbigniew Stojek; Kenneth R. Jeffrey (pp. 144-150).
Two methods have been used for examination of transport of charge in gels soaked with DMF and containing dissolved polyoxometallates. The first method is based on the analysis of both Cottrellian and steady-state currents and therefore is capable of giving the concentration of the electroactive redox centres and their transport (diffusion-type) coefficient. The second method provides the real diffusion coefficients, i.e. transport coefficients free of migrational influence, for both the substrate and the product of the electrode reaction. Several gels based on poly(methyl methacrylate), with charged (addition of 1-acrylamido-2-methyl-2-propanesulphonic acid to the polymerization mixture) and uncharged chains, have been used in the investigation. The ratio obtained for the diffusion coefficient (second method) and transport coefficient (first method) was smaller for the gels containing charged polymer chains than for the gels with uncharged chains. In part these changes could be explained by the contribution of migration to the transport of polyoxomatallates in the gels. However, the impact of the changes in the polymer-channel capacity at the electrode surface while the electrode process proceeds was also considered. These structural changes should affect differently the methods based on different time domains.
Keywords: Polymer gel; Solid-state electroanalysis; Migration; Diffusion coefficient; Concentration of redox sites
Analysis of charge transport in gels containing polyoxometallates using methods of different sensitivity to migration by Karolina Caban; Adam Lewera; Grazyna Z. Zukowska; Pawel J. Kulesza; Zbigniew Stojek; Kenneth R. Jeffrey (pp. 144-150).
Two methods have been used for examination of transport of charge in gels soaked with DMF and containing dissolved polyoxometallates. The first method is based on the analysis of both Cottrellian and steady-state currents and therefore is capable of giving the concentration of the electroactive redox centres and their transport (diffusion-type) coefficient. The second method provides the real diffusion coefficients, i.e. transport coefficients free of migrational influence, for both the substrate and the product of the electrode reaction. Several gels based on poly(methyl methacrylate), with charged (addition of 1-acrylamido-2-methyl-2-propanesulphonic acid to the polymerization mixture) and uncharged chains, have been used in the investigation. The ratio obtained for the diffusion coefficient (second method) and transport coefficient (first method) was smaller for the gels containing charged polymer chains than for the gels with uncharged chains. In part these changes could be explained by the contribution of migration to the transport of polyoxomatallates in the gels. However, the impact of the changes in the polymer-channel capacity at the electrode surface while the electrode process proceeds was also considered. These structural changes should affect differently the methods based on different time domains.
Keywords: Polymer gel; Solid-state electroanalysis; Migration; Diffusion coefficient; Concentration of redox sites