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Analytica Chimica Acta (v.578, #2)
Metal ion-imprinted polymers—Novel materials for selective recognition of inorganics by T. Prasada Rao; R. Kala; S. Daniel (pp. 105-116).
Ion-imprinted polymers (IIPs) are recently identified nano-porous polymeric materials which on leaching the imprint ion can rebind, sense or transport (when cast as membranes) selectively the target analyte in presence of closely related inorganic ions. The IIPs find interesting applications in solid phase extraction, sensors and membrane separations of inorganics. Unlike the molecularly imprinted polymers, the IIP field is in its infancy and has been briefly reviewed here along with some rough guidelines and concepts for further development of IIPs.
Keywords: Ion-imprinted polymers; Solid phase extraction; Sensors; Membrane separations; Inorganics
Metal ion-imprinted polymers—Novel materials for selective recognition of inorganics by T. Prasada Rao; R. Kala; S. Daniel (pp. 105-116).
Ion-imprinted polymers (IIPs) are recently identified nano-porous polymeric materials which on leaching the imprint ion can rebind, sense or transport (when cast as membranes) selectively the target analyte in presence of closely related inorganic ions. The IIPs find interesting applications in solid phase extraction, sensors and membrane separations of inorganics. Unlike the molecularly imprinted polymers, the IIP field is in its infancy and has been briefly reviewed here along with some rough guidelines and concepts for further development of IIPs.
Keywords: Ion-imprinted polymers; Solid phase extraction; Sensors; Membrane separations; Inorganics
Determination of total safranal by in situ acid hydrolysis in supercritical fluid media: Application to the quality control of commercial saffron by Mohammed Zougagh; Angel Ríos; Miguel Valcárcel (pp. 117-121).
A procedure allowing hydrolysis reactions to be conducted in a dynamic supercritical-CO2 medium was developed for quantifying total safranal ( viz. free safranal present in the sample+safranal resulting from picrocrocin hydrolysis), which are the main component of the essential oil and responsible for the characteristic aroma of saffron. The proposed method allows total safranal amounts over the ranges 0.05–1.5mgmL−1 to be determined. The standard deviation achieved was 2%. This method was applied to the determination of safranal in natural saffron samples. The results obtained were compared with the “safranal value? total index, which is widely used as a quality measure of saffron products. The comparison revealed that the proposed method provides useful information not contained in the safranal value, based on the fact that, some samples with a high “safranal index? contain low concentrations of safranal. The proposed method is very useful for quality control in commercial saffron samples.
Keywords: Supercritical fluid extraction; Quality control; Safranal; Saffron samples
Determination of total safranal by in situ acid hydrolysis in supercritical fluid media: Application to the quality control of commercial saffron by Mohammed Zougagh; Angel Ríos; Miguel Valcárcel (pp. 117-121).
A procedure allowing hydrolysis reactions to be conducted in a dynamic supercritical-CO2 medium was developed for quantifying total safranal ( viz. free safranal present in the sample+safranal resulting from picrocrocin hydrolysis), which are the main component of the essential oil and responsible for the characteristic aroma of saffron. The proposed method allows total safranal amounts over the ranges 0.05–1.5mgmL−1 to be determined. The standard deviation achieved was 2%. This method was applied to the determination of safranal in natural saffron samples. The results obtained were compared with the “safranal value” total index, which is widely used as a quality measure of saffron products. The comparison revealed that the proposed method provides useful information not contained in the safranal value, based on the fact that, some samples with a high “safranal index” contain low concentrations of safranal. The proposed method is very useful for quality control in commercial saffron samples.
Keywords: Supercritical fluid extraction; Quality control; Safranal; Saffron samples
Microwave-assisted extraction through an aqueous medium and simultaneous cleanup by partition on hexane for determining pesticides in agricultural soils by gas chromatography: A critical study by Edwar Fuentes; María E. Báez; Dana Reyes (pp. 122-130).
A simple microwave-assisted extraction and partitioning method (MAEP) using water–acetonitrile and n-hexane for desorption and simultaneous partitioning, respectively, together with gas chromatography (GC) was studied to determine representative pesticides (trifluralin, metolachlor, chlorpyriphos and triadimefon) with a broad range of physico-chemical properties in agricultural soils. Three points were considered crucial in this study: instrumental and sample-associated factors affecting extraction of the target compounds were studied through experimental design; the spiking procedure at trace levels was carried out to reproduce the solute-soil sorption taking place in the environment as closely as possible; and results were analyzed taking into account the adsorption behaviour of the compounds on different kinds of soils. The complete analytical procedure proposed consisted of the MAEP of pesticides from 1.0g of soil with 1mL of 1:1 water/acetonitrile mixture, and 5mL of hexane for trapping. The microwave heating program applied was 2min at 250W and 10min at 900W, and 130°C maximum temperature. After extraction, the hexane layer was evaporated to dryness; the residue was re-dissolved and directly analyzed by gas chromatography electron capture detection (GC-ECD). Clean chromatograms were obtained without any additional cleanup step. Besides the four pesticides used to optimise MAEP, the method was applied to determine an additional group of pesticides (triallate, acetochlor, alachlor, endosulphan I and II, endrin, methoxychlor and tetradifon) in different soils. Most of the compounds studied were recovered in good yields with relative standard deviations (R.S.D.s) below 9% and detection limits ranged from 0.004 to 0.036μgg−1. The described method is efficient and fast to determine hydrophobic pesticides at ngg−1 level in soil with different clay-to-organic matter ratios.
Keywords: Microwave-assisted extraction; Water–hexane partition; Pesticides; Soils
Microwave-assisted extraction through an aqueous medium and simultaneous cleanup by partition on hexane for determining pesticides in agricultural soils by gas chromatography: A critical study by Edwar Fuentes; María E. Báez; Dana Reyes (pp. 122-130).
A simple microwave-assisted extraction and partitioning method (MAEP) using water–acetonitrile and n-hexane for desorption and simultaneous partitioning, respectively, together with gas chromatography (GC) was studied to determine representative pesticides (trifluralin, metolachlor, chlorpyriphos and triadimefon) with a broad range of physico-chemical properties in agricultural soils. Three points were considered crucial in this study: instrumental and sample-associated factors affecting extraction of the target compounds were studied through experimental design; the spiking procedure at trace levels was carried out to reproduce the solute-soil sorption taking place in the environment as closely as possible; and results were analyzed taking into account the adsorption behaviour of the compounds on different kinds of soils. The complete analytical procedure proposed consisted of the MAEP of pesticides from 1.0g of soil with 1mL of 1:1 water/acetonitrile mixture, and 5mL of hexane for trapping. The microwave heating program applied was 2min at 250W and 10min at 900W, and 130°C maximum temperature. After extraction, the hexane layer was evaporated to dryness; the residue was re-dissolved and directly analyzed by gas chromatography electron capture detection (GC-ECD). Clean chromatograms were obtained without any additional cleanup step. Besides the four pesticides used to optimise MAEP, the method was applied to determine an additional group of pesticides (triallate, acetochlor, alachlor, endosulphan I and II, endrin, methoxychlor and tetradifon) in different soils. Most of the compounds studied were recovered in good yields with relative standard deviations (R.S.D.s) below 9% and detection limits ranged from 0.004 to 0.036μgg−1. The described method is efficient and fast to determine hydrophobic pesticides at ngg−1 level in soil with different clay-to-organic matter ratios.
Keywords: Microwave-assisted extraction; Water–hexane partition; Pesticides; Soils
Expression and characterization of insulin growth factor-I-enhanced green fluorescent protein fused protein as a tracer for immunoassay by Ruina Shi; Yong Huang; Dan Wang; Meiping Zhao; Yuanzong Li (pp. 131-136).
The insulin-like growth factor-I (IGF-I) is an important polypeptide hormone under investigation for body metabolism study and for doping detection. Here, we describe for the first time the expression of a recombinant fusion protein of IGF-I and the enhanced green fluorescent protein (EGFP). The genetic fusion approach enables preparation of conjugates with 1:1 stoichiometry and homogeneous structure. The fused protein (EGFP–IGF-I) was expressed as a soluble protein in cytoplasm of Escherichia coli and its fluorescence and immunoreaction properties were thoroughly characterized. Finally, we demonstrated the utility of the EGFP–IGF-I fusion protein for the fluorescence immunoassay of IGF-1. The linear range of the assay is 1.6×10−8 to 2.0×10−6M with a detection limit of 1.6×10−8M. To our knowledge, this is the first time that EGFP has been used as a quantitative label in a fusion protein to develop a quantitative assay for IGF-I. Furthermore, the use of genetically engineered fusion proteins, which combine peptide hormones with fluorescent protein, can lead to a new labeling approach to a number of bioanalytical applications.
Keywords: Insulin-like growth factor-I; Enhanced green fluorescent protein; Fused protein; Immunoassay
Expression and characterization of insulin growth factor-I-enhanced green fluorescent protein fused protein as a tracer for immunoassay by Ruina Shi; Yong Huang; Dan Wang; Meiping Zhao; Yuanzong Li (pp. 131-136).
The insulin-like growth factor-I (IGF-I) is an important polypeptide hormone under investigation for body metabolism study and for doping detection. Here, we describe for the first time the expression of a recombinant fusion protein of IGF-I and the enhanced green fluorescent protein (EGFP). The genetic fusion approach enables preparation of conjugates with 1:1 stoichiometry and homogeneous structure. The fused protein (EGFP–IGF-I) was expressed as a soluble protein in cytoplasm of Escherichia coli and its fluorescence and immunoreaction properties were thoroughly characterized. Finally, we demonstrated the utility of the EGFP–IGF-I fusion protein for the fluorescence immunoassay of IGF-1. The linear range of the assay is 1.6×10−8 to 2.0×10−6M with a detection limit of 1.6×10−8M. To our knowledge, this is the first time that EGFP has been used as a quantitative label in a fusion protein to develop a quantitative assay for IGF-I. Furthermore, the use of genetically engineered fusion proteins, which combine peptide hormones with fluorescent protein, can lead to a new labeling approach to a number of bioanalytical applications.
Keywords: Insulin-like growth factor-I; Enhanced green fluorescent protein; Fused protein; Immunoassay
Glucose biosensor based on the layer-by-layer self-assembling of glucose oxidase and chitosan derivatives on a thiolated gold surface by Silvia A. Miscoria; Jacques Desbrieres; Gustavo D. Barrera; Pierre Labbé; Gustavo A. Rivas (pp. 137-144).
The work proposed here deals with the design and characterization of biorecognition layers for the amperometric glucose determination based on the self-assembling of new chitosan derivatives, Nafion and glucose oxidase onto thiolated gold electrodes. The supramolecular multistructure is obtained by deposition of a layer of chitosan derivative (quaternized or hydrophobic) onto the gold surface modified with the sodium salt of 3-mercapto-1-propansulfonic acid, followed by the deposition of a layer of Nafion (as anti-interference barrier) and by the alternate deposition of the chitosan derivative and glucose oxidase (as biocatalytic layer). The influence of the deposition time and concentration of polyelectrolytes, organization and number of layers, and nature of the chitosan derivative on the sensitivity and selectivity of the bioelectrode is examined and optimized in order to obtain a rational design of the biosensor. The system is studied electrochemically from the oxidation at 0.700V of the hydrogen peroxide enzymatically generated using gold as substrate, and spectrophotometrically from the protein absorption at 277nm using quartz as substrate. The selected biosensor containing five quaternized chitosan/glucose oxidase bilayers exhibits very good analytical performance with a sensitive ((4.9±0.2)×102nAmM−1) and highly selective response (0% interference for maximum physiological levels of ascorbic acid and uric acid), demonstrating that the alternate electrostatic adsorption of conveniently selected polyelectrolytes allows noticeable improvements in the selectivity and sensitivity of a biosensor.
Keywords: Layer-by-layer deposition; Self-assembled multilayers; Enzymatic electrode; Glucose biosensor; Glucose oxidase; Chitosan; Gold; Nafion
Glucose biosensor based on the layer-by-layer self-assembling of glucose oxidase and chitosan derivatives on a thiolated gold surface by Silvia A. Miscoria; Jacques Desbrieres; Gustavo D. Barrera; Pierre Labbé; Gustavo A. Rivas (pp. 137-144).
The work proposed here deals with the design and characterization of biorecognition layers for the amperometric glucose determination based on the self-assembling of new chitosan derivatives, Nafion and glucose oxidase onto thiolated gold electrodes. The supramolecular multistructure is obtained by deposition of a layer of chitosan derivative (quaternized or hydrophobic) onto the gold surface modified with the sodium salt of 3-mercapto-1-propansulfonic acid, followed by the deposition of a layer of Nafion (as anti-interference barrier) and by the alternate deposition of the chitosan derivative and glucose oxidase (as biocatalytic layer). The influence of the deposition time and concentration of polyelectrolytes, organization and number of layers, and nature of the chitosan derivative on the sensitivity and selectivity of the bioelectrode is examined and optimized in order to obtain a rational design of the biosensor. The system is studied electrochemically from the oxidation at 0.700V of the hydrogen peroxide enzymatically generated using gold as substrate, and spectrophotometrically from the protein absorption at 277nm using quartz as substrate. The selected biosensor containing five quaternized chitosan/glucose oxidase bilayers exhibits very good analytical performance with a sensitive ((4.9±0.2)×102nAmM−1) and highly selective response (0% interference for maximum physiological levels of ascorbic acid and uric acid), demonstrating that the alternate electrostatic adsorption of conveniently selected polyelectrolytes allows noticeable improvements in the selectivity and sensitivity of a biosensor.
Keywords: Layer-by-layer deposition; Self-assembled multilayers; Enzymatic electrode; Glucose biosensor; Glucose oxidase; Chitosan; Gold; Nafion
Organoclay-enzyme film electrodes by Justin Kemmegne Mbouguen; Emmanuel Ngameni; Alain Walcarius (pp. 145-155).
This paper aims at showing the interest of organoclays (clay minerals containing organic groups covalently attached to the inorganic particles) as suitable host matrices likely to immobilize enzymes onto electrode surfaces for biosensing applications. The organoclays used in this work were natural Cameroonian smectites grafted with either aminopropyl (AP) or trimethylpropylammonium (TMPA) groups. The first ones were exploited for their ability to anchor biomolecules by covalent bonding while the second category exhibited favorable electrostatic interactions with negatively charged enzymes due to ion exchange properties that were pointed out here by means of multisweep cyclic voltammetry. AP-clay materials were applied to the immobilization of glucose oxidase (GOD) and TMPA-clays for polyphenol oxidase (PPO) anchoring. When deposited onto the surface of platinum or glassy carbon electrodes as enzyme/organoclay films, these systems were evaluated as biosensing electrochemical devices for detection of glucose and catechol chosen as model analytes. The advantageous features of these organoclays were discussed by comparison to the performance of related film electrodes made of non-functionalized clays. It appeared that organoclays provide a favorable environment to enzymes activity, as highlighted from the biosensors characteristics and determination of Michaelis–Menten constants.
Keywords: Organoclay; Enzyme; Modified electrode; Permselective film; Biosensor
Organoclay-enzyme film electrodes by Justin Kemmegne Mbouguen; Emmanuel Ngameni; Alain Walcarius (pp. 145-155).
This paper aims at showing the interest of organoclays (clay minerals containing organic groups covalently attached to the inorganic particles) as suitable host matrices likely to immobilize enzymes onto electrode surfaces for biosensing applications. The organoclays used in this work were natural Cameroonian smectites grafted with either aminopropyl (AP) or trimethylpropylammonium (TMPA) groups. The first ones were exploited for their ability to anchor biomolecules by covalent bonding while the second category exhibited favorable electrostatic interactions with negatively charged enzymes due to ion exchange properties that were pointed out here by means of multisweep cyclic voltammetry. AP-clay materials were applied to the immobilization of glucose oxidase (GOD) and TMPA-clays for polyphenol oxidase (PPO) anchoring. When deposited onto the surface of platinum or glassy carbon electrodes as enzyme/organoclay films, these systems were evaluated as biosensing electrochemical devices for detection of glucose and catechol chosen as model analytes. The advantageous features of these organoclays were discussed by comparison to the performance of related film electrodes made of non-functionalized clays. It appeared that organoclays provide a favorable environment to enzymes activity, as highlighted from the biosensors characteristics and determination of Michaelis–Menten constants.
Keywords: Organoclay; Enzyme; Modified electrode; Permselective film; Biosensor
A comparative study of immobilization techniques for urease on glass-pH-electrode and its application in urea detection in blood serum by Rachana Sahney; S. Anand; B.K. Puri; A.K. Srivastava (pp. 156-161).
Different techniques have been used (physical adsorption, physically entrapped sandwich and microencapsulation) for the immobilization of urease enzyme in tetramethylorthosilicate (TMOS) derived sol–gel matrix on the sensing surface of glass-pH-electrode. No significant leaching of enzyme occurs from the microencapsulated and physically entrapped enzyme sandwich films. Potentiometric techniques have been used for the estimation of urea concentration in each instance. Various parameters of biosensor performance have been studied which indicates that microencapsulation technique is a better method of enzyme immobilization in sol–gel films derived from TMOS. The advantage of microencapsulated biosensor over others include higher sensitivity (dpH/dp(C)=2.4), lower detection limit of 52μgmL−1, larger linear range (0.01–30mM) of urea determination and reasonably long-term stability of about 25 days with 80% response signal.
Keywords: pH-electrode; Physical adsorption; Physically entrapped sandwich; Microencapsulation; Sol–gel technique
A comparative study of immobilization techniques for urease on glass-pH-electrode and its application in urea detection in blood serum by Rachana Sahney; S. Anand; B.K. Puri; A.K. Srivastava (pp. 156-161).
Different techniques have been used (physical adsorption, physically entrapped sandwich and microencapsulation) for the immobilization of urease enzyme in tetramethylorthosilicate (TMOS) derived sol–gel matrix on the sensing surface of glass-pH-electrode. No significant leaching of enzyme occurs from the microencapsulated and physically entrapped enzyme sandwich films. Potentiometric techniques have been used for the estimation of urea concentration in each instance. Various parameters of biosensor performance have been studied which indicates that microencapsulation technique is a better method of enzyme immobilization in sol–gel films derived from TMOS. The advantage of microencapsulated biosensor over others include higher sensitivity (dpH/dp(C)=2.4), lower detection limit of 52μgmL−1, larger linear range (0.01–30mM) of urea determination and reasonably long-term stability of about 25 days with 80% response signal.
Keywords: pH-electrode; Physical adsorption; Physically entrapped sandwich; Microencapsulation; Sol–gel technique
Organophosphorus insecticides extraction and heterogeneous oxidation on column for analysis with an acetylcholinesterase (AChE) biosensor by Madalina Petruta Dondoi; Bogdan Bucur; Andrei Florin Danet; Constantin Nicolae Toader; Lise Barthelmebs; Jean-Louis Marty (pp. 162-169).
This paper presents an analysis method for organophosphorus insecticides based on AChE biosensors coupled with a preconcentration and oxidation on a solid phase column. Three organic solvents, acetonitrile (ACN), ethanol and methanol were tested for their influence on AChE activity, insecticide inhibition and their ability to elute the adsorbed insecticides. Our results showed that ACN in a concentration of 5% (v/v) had the less negative effect on biosensor analysis and was the most appropriate organic solvent for the column elution. The presence of the organic solvent in the incubation media of the biosensor was found to induce a reduction of the inhibition percentages. The inhibition of the biosensors was performed in phosphate buffer with 5% (v/v) ACN, while the initial and remaining response of the biosensors were measured in PBS. In these conditions, the LODs of paraoxon and dichlorvos were measured with or without a preconcentration step. The LODs of the AChE biosensor without sample preconcentration were 8×10−8M for paraoxon and 1×10−7M dichlorvos and the LOD obtained after the preconcentration step were 2.5×10−8M for paraoxon and 2.5×10−8M for dichlorvos. Moreover, the use of the column allowed the heterogeneous oxidation of organophosphorus insecticides for improved LOD.
Keywords: Acetylcholinesterase biosensor; Insecticide analysis; Column extraction; Organic phase biosensors; Screen-printed electrode
Organophosphorus insecticides extraction and heterogeneous oxidation on column for analysis with an acetylcholinesterase (AChE) biosensor by Madalina Petruta Dondoi; Bogdan Bucur; Andrei Florin Danet; Constantin Nicolae Toader; Lise Barthelmebs; Jean-Louis Marty (pp. 162-169).
This paper presents an analysis method for organophosphorus insecticides based on AChE biosensors coupled with a preconcentration and oxidation on a solid phase column. Three organic solvents, acetonitrile (ACN), ethanol and methanol were tested for their influence on AChE activity, insecticide inhibition and their ability to elute the adsorbed insecticides. Our results showed that ACN in a concentration of 5% (v/v) had the less negative effect on biosensor analysis and was the most appropriate organic solvent for the column elution. The presence of the organic solvent in the incubation media of the biosensor was found to induce a reduction of the inhibition percentages. The inhibition of the biosensors was performed in phosphate buffer with 5% (v/v) ACN, while the initial and remaining response of the biosensors were measured in PBS. In these conditions, the LODs of paraoxon and dichlorvos were measured with or without a preconcentration step. The LODs of the AChE biosensor without sample preconcentration were 8×10−8M for paraoxon and 1×10−7M dichlorvos and the LOD obtained after the preconcentration step were 2.5×10−8M for paraoxon and 2.5×10−8M for dichlorvos. Moreover, the use of the column allowed the heterogeneous oxidation of organophosphorus insecticides for improved LOD.
Keywords: Acetylcholinesterase biosensor; Insecticide analysis; Column extraction; Organic phase biosensors; Screen-printed electrode
A chemometric approach based on a novel similarity/diversity measure for the characterisation and selection of electronic nose sensors by Davide Ballabio; Maria Stella Cosio; Saverio Mannino; Roberto Todeschini (pp. 170-177).
Electronic nose sensor signals provide a digital fingerprint of the product in analysis, which can be subsequently investigated by means of chemometrics. In this paper, the fingerprint characterisation of electronic nose data has been studied by means of a novel chemometric approach based on the partial ordering technique and the Hasse matrix. This matrix can be associated to each data sequence and the similarity between two sequences can be evaluated with the definition of a distance between the corresponding Hasse matrices. Since all the signals achieved along time are intrinsically ordered, the data provided by electronic nose can be also considered as sequential data and consequently characterized by means of the proposed approach. The similarity/diversity measure has been here applied in order to characterize the class discrimination capability of each electronic nose sensor: extra virgin olive oil samples of different geographical origin have been considered and Hasse distances have been used to select the sensors which appear more able to discriminate the olive oil origins. The distance based on the Hasse matrix has showed some useful properties and proved to be able to link each electronic nose time profile to a meaningful mathematical term (the Hasse matrix), which can be consequently studied by multivariate analysis.
Keywords: Electronic nose; Time profile; Hasse; Partial ordering; Similarity/diversity; Class discrimination
A chemometric approach based on a novel similarity/diversity measure for the characterisation and selection of electronic nose sensors by Davide Ballabio; Maria Stella Cosio; Saverio Mannino; Roberto Todeschini (pp. 170-177).
Electronic nose sensor signals provide a digital fingerprint of the product in analysis, which can be subsequently investigated by means of chemometrics. In this paper, the fingerprint characterisation of electronic nose data has been studied by means of a novel chemometric approach based on the partial ordering technique and the Hasse matrix. This matrix can be associated to each data sequence and the similarity between two sequences can be evaluated with the definition of a distance between the corresponding Hasse matrices. Since all the signals achieved along time are intrinsically ordered, the data provided by electronic nose can be also considered as sequential data and consequently characterized by means of the proposed approach. The similarity/diversity measure has been here applied in order to characterize the class discrimination capability of each electronic nose sensor: extra virgin olive oil samples of different geographical origin have been considered and Hasse distances have been used to select the sensors which appear more able to discriminate the olive oil origins. The distance based on the Hasse matrix has showed some useful properties and proved to be able to link each electronic nose time profile to a meaningful mathematical term (the Hasse matrix), which can be consequently studied by multivariate analysis.
Keywords: Electronic nose; Time profile; Hasse; Partial ordering; Similarity/diversity; Class discrimination
The application of Kriging and empirical Kriging based on the variables selected by SCAD by Xiao-Ling Peng; Hong Yin; Runze Li; Kai-Tai Fang (pp. 178-185).
The commonly used approach for building a structure-activity/property relationship consists of three steps. First, one determines the descriptors for the molecular structure, then builds a metamodel by using some proper mathematical methods, and finally evaluates the meta-model. Some existing methods only can select important variables from the candidates, while most metamodels just explore linear relationships between inputs and outputs. Some techniques are useful to build more complicated relationship, but they may not be able to select important variables from a large number of variables. In this paper, we propose to screen important variables by the smoothly clipped absolute deviation (SCAD) variable selection procedure, and then apply Kriging model and empirical Kriging model for quantitative structure-activity/property relationship (QSAR/QSPR) research based on the selected important variables. We demonstrate the proposed procedure retains the virtues of both variable selection and Kriging model.
Keywords: Kriging models; Empirical Kriging; Penalized least squares; QSPR
The application of Kriging and empirical Kriging based on the variables selected by SCAD by Xiao-Ling Peng; Hong Yin; Runze Li; Kai-Tai Fang (pp. 178-185).
The commonly used approach for building a structure-activity/property relationship consists of three steps. First, one determines the descriptors for the molecular structure, then builds a metamodel by using some proper mathematical methods, and finally evaluates the meta-model. Some existing methods only can select important variables from the candidates, while most metamodels just explore linear relationships between inputs and outputs. Some techniques are useful to build more complicated relationship, but they may not be able to select important variables from a large number of variables. In this paper, we propose to screen important variables by the smoothly clipped absolute deviation (SCAD) variable selection procedure, and then apply Kriging model and empirical Kriging model for quantitative structure-activity/property relationship (QSAR/QSPR) research based on the selected important variables. We demonstrate the proposed procedure retains the virtues of both variable selection and Kriging model.
Keywords: Kriging models; Empirical Kriging; Penalized least squares; QSPR
Arsenic speciation analysis of human urine using ion exchange chromatography coupled to inductively coupled plasma mass spectrometry by Ruimin Xie; Willie Johnson; Steve Spayd; Gene S. Hall; Brian Buckley (pp. 186-194).
A sensitive and robust method for the determination of seven inorganic and organic arsenic species was developed using ion exchange chromatography combined with inductively coupled plasma mass spectrometry (IC-ICP-MS). Both anion and cation exchange columns were used in a complementary fashion. Arsenite (As(III)), arsenate (As(V)), monomethylarsonic acid (MMA(V)) and dimethylarsinic acid (DMA(V)) were selectively separated by an anion exchange column using sodium hydroxide (NaOH) gradient elution, while monomethylarsonous acid (MMA(III)), dimethylarsinous acid (DMA(III)) and arsenobetaine (AsB) were separated by a cation exchange column using 70mM nitric acid as the mobile phase. Baseline separation, high repeatability and low detection limits (0.10–0.75ngmL−1) were achieved. The spiked urine samples were analyzed with this method to evaluate the matrix effect on the method. The results suggest 1–10 dilutions should be made to urine samples before sample injection for the anion exchange analysis to minimize the matrix effect. To validate the method, a new standard reference material (NIST SRM-2670a) was also analyzed. The arsenic species in NIST SRM-2670a were determined by this method, and the sum of their concentrations agreed well with the total arsenic content certified for NIST SRM-2670a. Moreover, this method was applied to measure arsenic species in urine samples from one subject living in New Jersey who drank well water contaminated with arsenic. By this method, two key arsenic metabolites, MMA(III) and DMA(III), were found to be present in these urine samples, which has previously been rarely reported.
Keywords: Arsenic; Speciation; Urine; Ion chromatography–inductively coupled plasma mass spectrometry
Arsenic speciation analysis of human urine using ion exchange chromatography coupled to inductively coupled plasma mass spectrometry by Ruimin Xie; Willie Johnson; Steve Spayd; Gene S. Hall; Brian Buckley (pp. 186-194).
A sensitive and robust method for the determination of seven inorganic and organic arsenic species was developed using ion exchange chromatography combined with inductively coupled plasma mass spectrometry (IC-ICP-MS). Both anion and cation exchange columns were used in a complementary fashion. Arsenite (As(III)), arsenate (As(V)), monomethylarsonic acid (MMA(V)) and dimethylarsinic acid (DMA(V)) were selectively separated by an anion exchange column using sodium hydroxide (NaOH) gradient elution, while monomethylarsonous acid (MMA(III)), dimethylarsinous acid (DMA(III)) and arsenobetaine (AsB) were separated by a cation exchange column using 70mM nitric acid as the mobile phase. Baseline separation, high repeatability and low detection limits (0.10–0.75ngmL−1) were achieved. The spiked urine samples were analyzed with this method to evaluate the matrix effect on the method. The results suggest 1–10 dilutions should be made to urine samples before sample injection for the anion exchange analysis to minimize the matrix effect. To validate the method, a new standard reference material (NIST SRM-2670a) was also analyzed. The arsenic species in NIST SRM-2670a were determined by this method, and the sum of their concentrations agreed well with the total arsenic content certified for NIST SRM-2670a. Moreover, this method was applied to measure arsenic species in urine samples from one subject living in New Jersey who drank well water contaminated with arsenic. By this method, two key arsenic metabolites, MMA(III) and DMA(III), were found to be present in these urine samples, which has previously been rarely reported.
Keywords: Arsenic; Speciation; Urine; Ion chromatography–inductively coupled plasma mass spectrometry
Speciation of nickel in surface waters measured with the Donnan membrane technique by Liesbeth Van Laer; Erik Smolders; Fien Degryse; Colin Janssen; Karel A.C. De Schamphelaere (pp. 195-202).
The evaluation of the ecotoxicological risk of nickel (Ni) in surface water is hampered by a lack of speciation data. Six surface waters were sampled and speciation of Ni(II) was measured by the Donnan membrane technique (DMT) combined with radiochemical determination of63Ni. The free Ni2+ ion fraction in the dissolved (<0.45μm) phase was determined at background Ni concentration ((4–8)×10−8M) and at concentrations in the range of toxicity thresholds for the Ni sensitive species Cerodaphnia dubia (5×10−8 to 2×10−6M) . The free ion fraction ranged from 4 to 45% at background Ni and increased with increasing Ni concentration and water hardness and with decreasing pH. The equilibration time after addition of Ni2+ (3h–7d) did not significantly change the measured free ion fraction. Predictions of the Humic-Ion Binding Model WHAM (Windermere Humic Aqueous Model) VI overestimated the observed free Ni2+ fraction (median>two-fold), even when assuming that all dissolved organic matter (DOM) was present as fulvic acid (FA). The impact of several model parameters affecting the prediction of Ni speciation were evaluated, including the solubility product of Fe(OH)3, which affects the Fe competition for complexation by DOM. The best fit ( R2=0.88) was obtained by increasing only the distribution term ΔLK2, which modifies the binding strength of multi-dentate sites, to accommodate the observed dependence of free ion fraction on Ni concentration.
Keywords: Nickel speciation; Surface water; Windermere Humic Aqueous Model (WHAM); Donnan membrane technique (DMT)
Speciation of nickel in surface waters measured with the Donnan membrane technique by Liesbeth Van Laer; Erik Smolders; Fien Degryse; Colin Janssen; Karel A.C. De Schamphelaere (pp. 195-202).
The evaluation of the ecotoxicological risk of nickel (Ni) in surface water is hampered by a lack of speciation data. Six surface waters were sampled and speciation of Ni(II) was measured by the Donnan membrane technique (DMT) combined with radiochemical determination of63Ni. The free Ni2+ ion fraction in the dissolved (<0.45μm) phase was determined at background Ni concentration ((4–8)×10−8M) and at concentrations in the range of toxicity thresholds for the Ni sensitive species Cerodaphnia dubia (5×10−8 to 2×10−6M) . The free ion fraction ranged from 4 to 45% at background Ni and increased with increasing Ni concentration and water hardness and with decreasing pH. The equilibration time after addition of Ni2+ (3h–7d) did not significantly change the measured free ion fraction. Predictions of the Humic-Ion Binding Model WHAM (Windermere Humic Aqueous Model) VI overestimated the observed free Ni2+ fraction (median>two-fold), even when assuming that all dissolved organic matter (DOM) was present as fulvic acid (FA). The impact of several model parameters affecting the prediction of Ni speciation were evaluated, including the solubility product of Fe(OH)3, which affects the Fe competition for complexation by DOM. The best fit ( R2=0.88) was obtained by increasing only the distribution term ΔLK2, which modifies the binding strength of multi-dentate sites, to accommodate the observed dependence of free ion fraction on Ni concentration.
Keywords: Nickel speciation; Surface water; Windermere Humic Aqueous Model (WHAM); Donnan membrane technique (DMT)
Determination of tributyltin and 4-hydroxybutyldibutyltin chlorides in seawater by liquid chromatography with atmospheric pressure chemical ionization-mass spectrometry by K. Békri; R. Saint-Louis; É. Pelletier (pp. 203-212).
A liquid chromatographic method is described for the simultaneous determination of tributyltin (TBT) and the hydroxylated intermediate 4-hydroxybutyldibutyltin (OHBuDBT). Separation was achieved in reverse phase mode on a cyanopropyl-bonded silica column under a gradient elution. Various organic solvents and additives were tested and the optimum composition of the mobile phase contained methanol, water, formic acid and tropolone as a complexing agent. Butyltin compounds were detected with an ion trap mass spectrometer interfaced to a liquid chromatograph with an atmospheric pressure chemical ionization source (LC–APCI-MS). Identification and fragmentation pattern of OHBuDBT chloride in full scan MS and MS/MS are reported for the first time using LC–APCI-MS. Gas chromatography–mass spectrometry (GC–MS) spectrum of the same compound is also reported for the first time for comparison purpose. This method allowed limits of detection (LOD) of 35 and 26ngmL−1 for TBT and OHBuDBT, respectively, based on successive injections of 10μL of blank seawater extract. A liquid–liquid extraction procedure using n-hexane–ethyl acetate was developed for the simultaneous analysis of TBT and OHBuDBT chlorides in natural seawater and allowed average recoveries from 72 to 96% for the two compounds at three different spiking levels.
Keywords: Hydroxybutyldibutyltin; Tributyltin; Dibutyltin; Liquid chromatography–mass spectrometry; Seawater; Liquid–liquid extraction
Determination of tributyltin and 4-hydroxybutyldibutyltin chlorides in seawater by liquid chromatography with atmospheric pressure chemical ionization-mass spectrometry by K. Békri; R. Saint-Louis; É. Pelletier (pp. 203-212).
A liquid chromatographic method is described for the simultaneous determination of tributyltin (TBT) and the hydroxylated intermediate 4-hydroxybutyldibutyltin (OHBuDBT). Separation was achieved in reverse phase mode on a cyanopropyl-bonded silica column under a gradient elution. Various organic solvents and additives were tested and the optimum composition of the mobile phase contained methanol, water, formic acid and tropolone as a complexing agent. Butyltin compounds were detected with an ion trap mass spectrometer interfaced to a liquid chromatograph with an atmospheric pressure chemical ionization source (LC–APCI-MS). Identification and fragmentation pattern of OHBuDBT chloride in full scan MS and MS/MS are reported for the first time using LC–APCI-MS. Gas chromatography–mass spectrometry (GC–MS) spectrum of the same compound is also reported for the first time for comparison purpose. This method allowed limits of detection (LOD) of 35 and 26ngmL−1 for TBT and OHBuDBT, respectively, based on successive injections of 10μL of blank seawater extract. A liquid–liquid extraction procedure using n-hexane–ethyl acetate was developed for the simultaneous analysis of TBT and OHBuDBT chlorides in natural seawater and allowed average recoveries from 72 to 96% for the two compounds at three different spiking levels.
Keywords: Hydroxybutyldibutyltin; Tributyltin; Dibutyltin; Liquid chromatography–mass spectrometry; Seawater; Liquid–liquid extraction
Flame atomic absorption spectrometric determination of cadmium(II) and lead(II) after their solid phase extraction as dibenzyldithiocarbamate chelates on Dowex Optipore V-493 by Esra Melek; Mustafa Tuzen; Mustafa Soylak (pp. 213-219).
An enrichment procedure for cadmium and lead after their solid phase extraction as dibenzyldithiocarbamate chelates on Dowex Optipore V-493 has been established prior to their flame atomic absorption spectrometric determinations. The analytical parameters including pH, amounts of dibenzyldithiocarbamate, sample volume, etc., were investigated. The effects of alkaline and earth alkaline ions and some metal ions on the retentions of analytes on Dowex Optipore V-493 resin were examined. Under the optimized conditions, the detection limits (3s, n=21) for cadmium and lead were 0.43μgL−1 and 0.65μgL−1, respectively. The relative standard deviation (R.S.D.), and the recoveries of standard addition for this method were lower than 5% ( n=11) and 95–102%, respectively. Three standard reference samples (LGC 6010 Hard drinking water, NIST SRM 2711 Montana soil and GBW 07605 Tea) were introduced for accuracy and precision of analytical data. The proposed solid phase extraction system was successfully applied to the analysis of environmental samples.
Keywords: Solid phase extraction; Sodium dibenzyldithiocarbamate; Dowex Optipore V-493; Flame atomic absorption spectrometry
Flame atomic absorption spectrometric determination of cadmium(II) and lead(II) after their solid phase extraction as dibenzyldithiocarbamate chelates on Dowex Optipore V-493 by Esra Melek; Mustafa Tuzen; Mustafa Soylak (pp. 213-219).
An enrichment procedure for cadmium and lead after their solid phase extraction as dibenzyldithiocarbamate chelates on Dowex Optipore V-493 has been established prior to their flame atomic absorption spectrometric determinations. The analytical parameters including pH, amounts of dibenzyldithiocarbamate, sample volume, etc., were investigated. The effects of alkaline and earth alkaline ions and some metal ions on the retentions of analytes on Dowex Optipore V-493 resin were examined. Under the optimized conditions, the detection limits (3s, n=21) for cadmium and lead were 0.43μgL−1 and 0.65μgL−1, respectively. The relative standard deviation (R.S.D.), and the recoveries of standard addition for this method were lower than 5% ( n=11) and 95–102%, respectively. Three standard reference samples (LGC 6010 Hard drinking water, NIST SRM 2711 Montana soil and GBW 07605 Tea) were introduced for accuracy and precision of analytical data. The proposed solid phase extraction system was successfully applied to the analysis of environmental samples.
Keywords: Solid phase extraction; Sodium dibenzyldithiocarbamate; Dowex Optipore V-493; Flame atomic absorption spectrometry
Chromatographic determination of flumequine in food samples by post-column derivatisation with terbium(III) by R.C. Rodríguez-Díaz; J.M. Fernández-Romero; M.P. Aguilar-Caballos; A. Gómez-Hens (pp. 220-226).
The potential usefulness of terbium(III) as reagent for the luminescent determination of flumequine residues in food samples has been studied using both fluorescence (FL) and time-resolved (TR) modes and both batch (B) and integrated liquid chromatography (LC)/derivatisation approaches. The system was optimised in each instance to establish the analytical features of the four methods. The dynamic ranges of the calibration graphs, obtained with standard solutions of flumequine, were (ngmL−1): B-FL 0.18–600; B-TR 2.4–150; LC-FL 3.7–1000 and LC-TR 52–3000. The detection limits were also obtained giving the following values (ngmL−1): B-FL 0.055; B-TR 0.7; LC-FL 1.1 and LC-TR 15. The precision, expressed as the percentage of relative standard deviation, was equal or lower than 5.1% in all instances. The LC methods, which avoid the interference of other quinolone antibiotics, were applied to the analysis of chicken muscle and liver, and whole milk samples. The sample pre-treatment only consisted of a deproteinisation step. The validation procedure for the analysis of samples was carried out using EC recommendations, and the decision limit and detection capability were calculated. The recoveries obtained ranged from 95.0% to 103.8%.
Keywords: Flumequine; Terbium(III); Fluorescence and time-resolved detection; Liquid chromatography; Food samples
Chromatographic determination of flumequine in food samples by post-column derivatisation with terbium(III) by R.C. Rodríguez-Díaz; J.M. Fernández-Romero; M.P. Aguilar-Caballos; A. Gómez-Hens (pp. 220-226).
The potential usefulness of terbium(III) as reagent for the luminescent determination of flumequine residues in food samples has been studied using both fluorescence (FL) and time-resolved (TR) modes and both batch (B) and integrated liquid chromatography (LC)/derivatisation approaches. The system was optimised in each instance to establish the analytical features of the four methods. The dynamic ranges of the calibration graphs, obtained with standard solutions of flumequine, were (ngmL−1): B-FL 0.18–600; B-TR 2.4–150; LC-FL 3.7–1000 and LC-TR 52–3000. The detection limits were also obtained giving the following values (ngmL−1): B-FL 0.055; B-TR 0.7; LC-FL 1.1 and LC-TR 15. The precision, expressed as the percentage of relative standard deviation, was equal or lower than 5.1% in all instances. The LC methods, which avoid the interference of other quinolone antibiotics, were applied to the analysis of chicken muscle and liver, and whole milk samples. The sample pre-treatment only consisted of a deproteinisation step. The validation procedure for the analysis of samples was carried out using EC recommendations, and the decision limit and detection capability were calculated. The recoveries obtained ranged from 95.0% to 103.8%.
Keywords: Flumequine; Terbium(III); Fluorescence and time-resolved detection; Liquid chromatography; Food samples
Determination of capsaicinoids in peppers by microwave-assisted extraction–high-performance liquid chromatography with fluorescence detection by Gerardo F. Barbero; Miguel Palma; Carmelo G. Barroso (pp. 227-233).
A new method has been developed for the extraction of capsaicinoids (nordihydrocapsaicin, capsaicin, dihydrocapsaicin, homocapsaicin and homodihydrocapsaicin) in peppers employing microwave-assisted extraction. The parameters studied are: extraction solvent (methanol, ethanol, acetone, ethyl acetate and water), temperature (50–200°C), sample quantity (0.1–1g), volume of solvent (15–50mL) and the extraction time (5–20min). The results found for the optimum conditions are: 125°C as extraction temperature, 25mL of solvent, 0.5g of freshly triturated peppers and extraction for 5min, employing 100% ethanol as solvent. The capsaicinoids obtained were stable under the optimised extraction conditions. The resulting method presents a high degree of reproducibility (R.S.D.<6%).
Keywords: Microwave-assisted extraction; Capsaicinoids; Peppers
Determination of capsaicinoids in peppers by microwave-assisted extraction–high-performance liquid chromatography with fluorescence detection by Gerardo F. Barbero; Miguel Palma; Carmelo G. Barroso (pp. 227-233).
A new method has been developed for the extraction of capsaicinoids (nordihydrocapsaicin, capsaicin, dihydrocapsaicin, homocapsaicin and homodihydrocapsaicin) in peppers employing microwave-assisted extraction. The parameters studied are: extraction solvent (methanol, ethanol, acetone, ethyl acetate and water), temperature (50–200°C), sample quantity (0.1–1g), volume of solvent (15–50mL) and the extraction time (5–20min). The results found for the optimum conditions are: 125°C as extraction temperature, 25mL of solvent, 0.5g of freshly triturated peppers and extraction for 5min, employing 100% ethanol as solvent. The capsaicinoids obtained were stable under the optimised extraction conditions. The resulting method presents a high degree of reproducibility (R.S.D.<6%).
Keywords: Microwave-assisted extraction; Capsaicinoids; Peppers
Direct determination of acrylamide in food by gas chromatography–high-resolution time-of-flight mass spectrometry by Lenka Dunovská; Tomáš Čajka; Jana Hajšlová; Kateřina Holadová (pp. 234-240).
Simple and rapid gas chromatographic (GC) method employing a high-resolution time-of-flight mass analyzer that enables direct analysis (no derivatization) of acrylamide in various heat-processed foodstuffs has been developed and validated. Co-isolation of acrylamide precursors such as sugars and asparagine, constituting the risk of results overestimation due to additional formation of analyte in hot GC injector, is avoided by the extraction with n-propanol followed by solvent exchange to acetonitrile (MeCN). Introduction of a novel purification strategy, dispersive solid phase extraction, based on addition of primary-secondary amine (PSA) sorbent into deffated extract in MeCN, provides a significant reduction of some abundant matrix co-extracts (mainly free fatty acids). Isotope dilution technique (d3-acrylamide as an internal standard) is employed for compensation of potential target analyte losses and/or matrix-inducted chromatographic response enhancement. Limits of quantifications (LOQs) ranged between 15 and 40μgkg−1 and recoveries were between 97 and 108% depending on the examined food matrix. The repeatability of measurements (expressed as relative standard deviation, R.S.D.) was as low as 1.9% for potato crisps containing acrylamide at a level of 1mgkg−1. Slightly higher values (R.S.D.<4.0%) were achieved for breakfast cereals and crisp bread with approximately 10 times lower content of this processing contaminant. Trueness of results generated by this new method was demonstrated via FAPAS® (Food Analysis Performance Assessment Scheme) interlaboratory proficiency tests.
Keywords: Acrylamide; Gas chromatography; High-resolution time-of-flight mass spectrometry; Food analysis
Direct determination of acrylamide in food by gas chromatography–high-resolution time-of-flight mass spectrometry by Lenka Dunovská; Tomáš Čajka; Jana Hajšlová; Kateřina Holadová (pp. 234-240).
Simple and rapid gas chromatographic (GC) method employing a high-resolution time-of-flight mass analyzer that enables direct analysis (no derivatization) of acrylamide in various heat-processed foodstuffs has been developed and validated. Co-isolation of acrylamide precursors such as sugars and asparagine, constituting the risk of results overestimation due to additional formation of analyte in hot GC injector, is avoided by the extraction with n-propanol followed by solvent exchange to acetonitrile (MeCN). Introduction of a novel purification strategy, dispersive solid phase extraction, based on addition of primary-secondary amine (PSA) sorbent into deffated extract in MeCN, provides a significant reduction of some abundant matrix co-extracts (mainly free fatty acids). Isotope dilution technique (d3-acrylamide as an internal standard) is employed for compensation of potential target analyte losses and/or matrix-inducted chromatographic response enhancement. Limits of quantifications (LOQs) ranged between 15 and 40μgkg−1 and recoveries were between 97 and 108% depending on the examined food matrix. The repeatability of measurements (expressed as relative standard deviation, R.S.D.) was as low as 1.9% for potato crisps containing acrylamide at a level of 1mgkg−1. Slightly higher values (R.S.D.<4.0%) were achieved for breakfast cereals and crisp bread with approximately 10 times lower content of this processing contaminant. Trueness of results generated by this new method was demonstrated via FAPAS® (Food Analysis Performance Assessment Scheme) interlaboratory proficiency tests.
Keywords: Acrylamide; Gas chromatography; High-resolution time-of-flight mass spectrometry; Food analysis
Determination of herbicides by solid phase extraction gas chromatography–mass spectrometry in drinking waters by M.C. Bruzzoniti; C. Sarzanini; G. Costantino; M. Fungi (pp. 241-249).
A solid phase extraction (SPE) method has been optimized for the gas chromatography–mass spectrometry (GC–MS) simultaneous determination of herbicides belonging to the following different families: carbamate (molinate), atrazines (atrazine, propazine, simazine, ametryne, cyanazine, terbutylazine, deethylterbutylazine, deethylatrazine), dinitroaniline (trifluralin, pendimethalin), chloroacetamide (alachlor, metolachlor). Different solid substrates have been compared (C18, cyano, styrene–divinylbenzene, phenyl, graphitic carbon). The type of conditioning and elution solvent, its volume, and the sample flow rate have been considered as variables affecting the recovery yields of the herbicides.The optimized experimental conditions are C18 phase conditioned with 3mL acetone, loaded with 1L water sample at 5mLmin−1, and eluted with 3mL acetone. Good recoveries (included between 79% and 99%) and R.S.D. (included between 2% and 12%) have been obtained for all analytes, except for deethylatrazine whose recovery was 46±7%. The recovery of deethylatrazine increases up to 94±17% if a non-porous graphitic carbon is coupled to the C18 phase, keeping the other parameters constant as optimized. The optimized method has been successfully checked for the identification and quantitation of the selected herbicides in raw and drinking water samples, with quantitation limits as low as 0.01μgL−1, fully in agreement with the current legislation. The method is easily routinable. After development, the method is currently routinely applied for the analysis of herbicides in waters and, up today, more than one thousand samples have been analysed at the “Laboratorio della Società Metropolitana Acque di Torino? (Laboratory of the Municipal Waterworks of Turin) in charge of the control of drinking water quality in Torino.
Keywords: Herbicides; Solid phase extraction substrates; Gas chromatography–mass spectrometry; Drinking waters; Raw waters
Determination of herbicides by solid phase extraction gas chromatography–mass spectrometry in drinking waters by M.C. Bruzzoniti; C. Sarzanini; G. Costantino; M. Fungi (pp. 241-249).
A solid phase extraction (SPE) method has been optimized for the gas chromatography–mass spectrometry (GC–MS) simultaneous determination of herbicides belonging to the following different families: carbamate (molinate), atrazines (atrazine, propazine, simazine, ametryne, cyanazine, terbutylazine, deethylterbutylazine, deethylatrazine), dinitroaniline (trifluralin, pendimethalin), chloroacetamide (alachlor, metolachlor). Different solid substrates have been compared (C18, cyano, styrene–divinylbenzene, phenyl, graphitic carbon). The type of conditioning and elution solvent, its volume, and the sample flow rate have been considered as variables affecting the recovery yields of the herbicides.The optimized experimental conditions are C18 phase conditioned with 3mL acetone, loaded with 1L water sample at 5mLmin−1, and eluted with 3mL acetone. Good recoveries (included between 79% and 99%) and R.S.D. (included between 2% and 12%) have been obtained for all analytes, except for deethylatrazine whose recovery was 46±7%. The recovery of deethylatrazine increases up to 94±17% if a non-porous graphitic carbon is coupled to the C18 phase, keeping the other parameters constant as optimized. The optimized method has been successfully checked for the identification and quantitation of the selected herbicides in raw and drinking water samples, with quantitation limits as low as 0.01μgL−1, fully in agreement with the current legislation. The method is easily routinable. After development, the method is currently routinely applied for the analysis of herbicides in waters and, up today, more than one thousand samples have been analysed at the “Laboratorio della Società Metropolitana Acque di Torino” (Laboratory of the Municipal Waterworks of Turin) in charge of the control of drinking water quality in Torino.
Keywords: Herbicides; Solid phase extraction substrates; Gas chromatography–mass spectrometry; Drinking waters; Raw waters
Identifying constituents in commercial gasoline using Fourier transform-infrared spectroscopy and independent component analysis by Nikos Pasadakis; Andreas A. Kardamakis (pp. 250-255).
A new method is proposed that enables the identification of five refinery fractions present in commercial gasoline mixtures using infrared spectroscopic analysis. The data analysis and interpretation was carried out based on independent component analysis (ICA) and spectral similarity techniques. The FT-IR spectra of the gasoline constituents were determined using the ICA method, exclusively based on the spectra of their mixtures as a blind separation procedure, i.e. assuming unknown the spectra of the constituents. The identity of the constituents was subsequently determined using similarity measures commonly employed in spectra library searches against the spectra of the constituent components. The high correlation scores that were obtained in the identification of the constituents indicates that the developed method can be employed as a rapid and effective tool in quality control, fingerprinting or forensic applications, where gasoline constituents are suspected.
Keywords: Gasoline; Independent component analysis; Infrared spectroscopy
Identifying constituents in commercial gasoline using Fourier transform-infrared spectroscopy and independent component analysis by Nikos Pasadakis; Andreas A. Kardamakis (pp. 250-255).
A new method is proposed that enables the identification of five refinery fractions present in commercial gasoline mixtures using infrared spectroscopic analysis. The data analysis and interpretation was carried out based on independent component analysis (ICA) and spectral similarity techniques. The FT-IR spectra of the gasoline constituents were determined using the ICA method, exclusively based on the spectra of their mixtures as a blind separation procedure, i.e. assuming unknown the spectra of the constituents. The identity of the constituents was subsequently determined using similarity measures commonly employed in spectra library searches against the spectra of the constituent components. The high correlation scores that were obtained in the identification of the constituents indicates that the developed method can be employed as a rapid and effective tool in quality control, fingerprinting or forensic applications, where gasoline constituents are suspected.
Keywords: Gasoline; Independent component analysis; Infrared spectroscopy