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Analytica Chimica Acta (v.585, #2)
Colloidal nanoparticle analysis by nanoelectrospray size spectrometry with a heated flow by I. Wuled Lenggoro; Hendri Widiyandari; Christopher J. Hogan Jr.; Pratim Biswas; Kikuo Okuyama (pp. 193-201).
A nanoelectrospray–furnace–scanning mobility particle spectrometer (SMPS) system was developed which is capable of rapidly and accurately measuring the size distributions of colloidal nanoparticles. Many colloidal suspensions require the use of nonvolatile surfactants to stabilize the suspensions. Nonvolatile materials coat colloidal particles and form residue particles during the electrospray process; thus, SMPS measurements are normally inaccurate for colloidal particles. Here, a tubular furnace reactor is used to evaporate residue nanoparticles and coatings, which allows for correct nanoparticle size measurement. Test suspensions of silver, gold, and SiO2 nanoparticles were measured in the electrospray–furnace–SMPS system. SMPS measurements and field emission scanning electron microscopy measurements were in excellent agreement for all test suspensions. High-temperature heating in the furnace was used to evaporate the nanoparticles themselves, which shifted the nanoparticle size spectra to smaller sizes, allowing for thermal analysis to be performed on colloidal suspensions in addition to size measurement.
Keywords: Nanoparticles; Size spectrometry; Differential mobility analysis; Electrospray; Thermal analysis
Colloidal nanoparticle analysis by nanoelectrospray size spectrometry with a heated flow by I. Wuled Lenggoro; Hendri Widiyandari; Christopher J. Hogan Jr.; Pratim Biswas; Kikuo Okuyama (pp. 193-201).
A nanoelectrospray–furnace–scanning mobility particle spectrometer (SMPS) system was developed which is capable of rapidly and accurately measuring the size distributions of colloidal nanoparticles. Many colloidal suspensions require the use of nonvolatile surfactants to stabilize the suspensions. Nonvolatile materials coat colloidal particles and form residue particles during the electrospray process; thus, SMPS measurements are normally inaccurate for colloidal particles. Here, a tubular furnace reactor is used to evaporate residue nanoparticles and coatings, which allows for correct nanoparticle size measurement. Test suspensions of silver, gold, and SiO2 nanoparticles were measured in the electrospray–furnace–SMPS system. SMPS measurements and field emission scanning electron microscopy measurements were in excellent agreement for all test suspensions. High-temperature heating in the furnace was used to evaporate the nanoparticles themselves, which shifted the nanoparticle size spectra to smaller sizes, allowing for thermal analysis to be performed on colloidal suspensions in addition to size measurement.
Keywords: Nanoparticles; Size spectrometry; Differential mobility analysis; Electrospray; Thermal analysis
Behaviour of palladium(II), platinum(IV), and rhodium(III) in artificial and natural waters: Influence of reactor surface and geochemistry on metal recovery by Antonio Cobelo-Garcia; Andrew Turner; Geoffrey E. Millward; Fay Couceiro (pp. 202-210).
The recovery of dissolved platinum group elements (PGE: Pd(II), Pt(IV) and Rh(III)) added to Milli-Q® water, artificial freshwater and seawater and filtered natural waters has been studied, as a function of pH and PGE concentration, in containers of varying synthetic composition. The least adsorptive and/or precipitative loss was obtained for borosilicate glass under most of the conditions employed, whereas the greatest loss was obtained for low-density polyethylene. Of the polymeric materials tested, the adsorptive and/or precipitative loss of PGE was lowest for fluorinated ethylene propylene (Teflon®). The loss of Pd(II) in freshwater was significant due to its affinity for surface adsorption and its relatively low solubility. The presence of natural dissolved organic matter increases the recovery of Pd(II) but enhances the loss of Pt(IV). The loss of Rh(III) in seawater was significant and was mainly due to precipitation, whereas Pd(II) recovery was enhanced, compared to freshwater, because of its complexation with chloride. The results have important implications regarding protocols employed for sample preservation and controlled laboratory experiments used in the study of the speciation and biogeochemical behaviour of PGE.
Keywords: Platinum group elements; Speciation; Adsorption; Precipitation; Container materials
Behaviour of palladium(II), platinum(IV), and rhodium(III) in artificial and natural waters: Influence of reactor surface and geochemistry on metal recovery by Antonio Cobelo-Garcia; Andrew Turner; Geoffrey E. Millward; Fay Couceiro (pp. 202-210).
The recovery of dissolved platinum group elements (PGE: Pd(II), Pt(IV) and Rh(III)) added to Milli-Q® water, artificial freshwater and seawater and filtered natural waters has been studied, as a function of pH and PGE concentration, in containers of varying synthetic composition. The least adsorptive and/or precipitative loss was obtained for borosilicate glass under most of the conditions employed, whereas the greatest loss was obtained for low-density polyethylene. Of the polymeric materials tested, the adsorptive and/or precipitative loss of PGE was lowest for fluorinated ethylene propylene (Teflon®). The loss of Pd(II) in freshwater was significant due to its affinity for surface adsorption and its relatively low solubility. The presence of natural dissolved organic matter increases the recovery of Pd(II) but enhances the loss of Pt(IV). The loss of Rh(III) in seawater was significant and was mainly due to precipitation, whereas Pd(II) recovery was enhanced, compared to freshwater, because of its complexation with chloride. The results have important implications regarding protocols employed for sample preservation and controlled laboratory experiments used in the study of the speciation and biogeochemical behaviour of PGE.
Keywords: Platinum group elements; Speciation; Adsorption; Precipitation; Container materials
Preparation of silica-supported porous sorbent for heavy metal ions removal in wastewater treatment by organic–inorganic hybridization combined with sucrose and polyethylene glycol imprinting by Feng Li; Ping Du; Wei Chen; Shusheng Zhang (pp. 211-218).
A new porous sorbent for wastewater treatment of metal ions was synthesized by covalent grafting of molecularly imprinted organic–inorganic hybrid on silica gel. With sucrose and polyethylene glycol 4000 (PEG 4000) being synergic imprinting molecules, covalent surface coating on silica gel was achieved by using polysaccharide-incorporated sol–gel process starting from the functional biopolymer, chitosan and an inorganic epoxy-precursor, gamma-glycidoxypropyltrimethoxysiloxane (GPTMS) at room temperature. The prepared porous sorbent was characterized by using simultaneous thermogravimetry and differential scanning calorimeter (TG/DSC), scanning electron microscopy (SEM), nitrogen adsorption porosimetry measurement and X-ray diffraction (XRD). Copper ion, Cu2+, was chosen as the model metal ion to evaluate the effectiveness of the new biosorbent in wastewater treatment. The influence of epoxy-siloxane dose, buffer pH and co-existed ions on Cu2+ adsorption was assessed through batch experiments. The imprinted composite sorbent offered a fast kinetics for the adsorption of Cu2+. The uptake capacity of the sorbent imprinted by two pore-building components was higher than those imprinted with only a single component. The dynamic adsorption in column underwent a good elimination of Cu2+ in treating electric plating wastewater. The prepared composite sorbent exhibited high reusability. Easy preparation of the described porous composite sorbent, absence of organic solvents, cost-effectiveness and high stability make this approach attractive in biosorption.
Keywords: Organic–inorganic; Hybrid; Chitosan; Imprinting; Sol–gel; Sorbent; Silica gel; Porous
Preparation of silica-supported porous sorbent for heavy metal ions removal in wastewater treatment by organic–inorganic hybridization combined with sucrose and polyethylene glycol imprinting by Feng Li; Ping Du; Wei Chen; Shusheng Zhang (pp. 211-218).
A new porous sorbent for wastewater treatment of metal ions was synthesized by covalent grafting of molecularly imprinted organic–inorganic hybrid on silica gel. With sucrose and polyethylene glycol 4000 (PEG 4000) being synergic imprinting molecules, covalent surface coating on silica gel was achieved by using polysaccharide-incorporated sol–gel process starting from the functional biopolymer, chitosan and an inorganic epoxy-precursor, gamma-glycidoxypropyltrimethoxysiloxane (GPTMS) at room temperature. The prepared porous sorbent was characterized by using simultaneous thermogravimetry and differential scanning calorimeter (TG/DSC), scanning electron microscopy (SEM), nitrogen adsorption porosimetry measurement and X-ray diffraction (XRD). Copper ion, Cu2+, was chosen as the model metal ion to evaluate the effectiveness of the new biosorbent in wastewater treatment. The influence of epoxy-siloxane dose, buffer pH and co-existed ions on Cu2+ adsorption was assessed through batch experiments. The imprinted composite sorbent offered a fast kinetics for the adsorption of Cu2+. The uptake capacity of the sorbent imprinted by two pore-building components was higher than those imprinted with only a single component. The dynamic adsorption in column underwent a good elimination of Cu2+ in treating electric plating wastewater. The prepared composite sorbent exhibited high reusability. Easy preparation of the described porous composite sorbent, absence of organic solvents, cost-effectiveness and high stability make this approach attractive in biosorption.
Keywords: Organic–inorganic; Hybrid; Chitosan; Imprinting; Sol–gel; Sorbent; Silica gel; Porous
A study of reproducibility of guanidination–dimethylation labeling and liquid chromatography matrix-assisted laser desorption ionization mass spectrometry for relative proteome quantification by Chengjie Ji; Nan Zhang; Sambasivarao Damaraju; Vijaya L. Damaraju; Pat Carpenter; Carol E. Cass; Liang Li (pp. 219-226).
The combination ofdimethylation afterguanidination (2MEGA) isotope labeling with microbore liquid chromatography (LC)-matrix-assisted laser desorption ionization (MALDI) MS and MS/MS [C. Ji, N. Guo, L. Li, J. Proteome Res. 4 (2005) 2099] has been reported as a promising strategy for abundance ratio-dependent quantitative proteome analysis. A critical step in using this integrated strategy is to set up the abundance ratio threshold of peptide pairs, above which the peptide pairs are used for quantifying and identifying the protein that is considered to be differentially expressed between two different samples. The threshold is determined by technical variation (i.e., the overall abundance ratio variation caused by the experimental process including sample workup, MS analysis and data processing) as well as biological variation (i.e., the abundance ratio variation caused by the biological process including cell growth), which can be defined and assessed by a coefficient of variation (CV). We have designed experiments and measured three different levels of variations, starting with the same membrane protein preparation, the same batch of cells and three batches of cells from the same cell line grown under the same conditions, respectively. It is shown that technical variation from the experimental processes involved in 2MEGA labeling LC-MALDI MS has a CV of <15%. In addition, the measured biological variation from cell growth was much smaller than the measured technical variation. From the studies of the occurrence rate of outliers in the distribution of the abundance ratio data within a comparative dataset of peptide pairs, it is concluded that, to compare the proteome changes between two sets of cultured cells without the use of replicate experiments, a relative abundance ratio of greater than 2 X or less than 0.5 X ( X is the average abundance ratio of the dataset) on peptide pairs can be used as a stringent threshold to quantify and identify differentially expressed proteins with high confidence.
Keywords: Dimethylation; Guanidination; Dimethylation after guanidination; Isotope labeling; Liquid chromatography matrix-assisted laser desorption ionization; Proteome quantification
A study of reproducibility of guanidination–dimethylation labeling and liquid chromatography matrix-assisted laser desorption ionization mass spectrometry for relative proteome quantification by Chengjie Ji; Nan Zhang; Sambasivarao Damaraju; Vijaya L. Damaraju; Pat Carpenter; Carol E. Cass; Liang Li (pp. 219-226).
The combination ofdimethylation afterguanidination (2MEGA) isotope labeling with microbore liquid chromatography (LC)-matrix-assisted laser desorption ionization (MALDI) MS and MS/MS [C. Ji, N. Guo, L. Li, J. Proteome Res. 4 (2005) 2099] has been reported as a promising strategy for abundance ratio-dependent quantitative proteome analysis. A critical step in using this integrated strategy is to set up the abundance ratio threshold of peptide pairs, above which the peptide pairs are used for quantifying and identifying the protein that is considered to be differentially expressed between two different samples. The threshold is determined by technical variation (i.e., the overall abundance ratio variation caused by the experimental process including sample workup, MS analysis and data processing) as well as biological variation (i.e., the abundance ratio variation caused by the biological process including cell growth), which can be defined and assessed by a coefficient of variation (CV). We have designed experiments and measured three different levels of variations, starting with the same membrane protein preparation, the same batch of cells and three batches of cells from the same cell line grown under the same conditions, respectively. It is shown that technical variation from the experimental processes involved in 2MEGA labeling LC-MALDI MS has a CV of <15%. In addition, the measured biological variation from cell growth was much smaller than the measured technical variation. From the studies of the occurrence rate of outliers in the distribution of the abundance ratio data within a comparative dataset of peptide pairs, it is concluded that, to compare the proteome changes between two sets of cultured cells without the use of replicate experiments, a relative abundance ratio of greater than 2 X or less than 0.5 X ( X is the average abundance ratio of the dataset) on peptide pairs can be used as a stringent threshold to quantify and identify differentially expressed proteins with high confidence.
Keywords: Dimethylation; Guanidination; Dimethylation after guanidination; Isotope labeling; Liquid chromatography matrix-assisted laser desorption ionization; Proteome quantification
Effect of alkylimidazolium substituents on enantioseparation ability of single-isomer alkylimidazolium-β-cyclodextrin derivatives in capillary electrophoresis by Weihua Tang; Teng-Teng Ong; I. Wayan Muderawan; Siu Choon Ng (pp. 227-233).
A family of 6-mono(3-alkylimidazolium)-β-cyclodextrins with one primary hydroxyl group replaced by an alkylimidazolium cation has been developed. The effect of alkyl substitutents on the enantioresolution ability of these single-isomer cyclodextrins towards dansyl amino acids has been studied by capillary electrophoresis. Systematical investigations on the effect of buffer pH and selector concentration on the enatioseparation show that chiral selectors with a shorter alkyl chain (R=C nH2 n+1, n≤4) presented more powerful chiral recognition ability. These newly introduced single-isomer β-cyclodextrin derivatives proved to be effective chiral selectors for most selected dansyl amino acids at low buffer pH (e.g. pH 5.0) with selector concentration no less than 3mM. The apparent complex stability constants between alkylimidazolium β-CDs and dansyl amino acids were also theoretically determined by using the mobility difference model proposed by Wren and Rowe. The side alkyl chains from both dansyl amino acids and alkylimidazolium β-CDs displayed significant effect on the apparent complex stability constants. Both the optimum selector concentrations calculated according to the model, however, were much lower than the experimental values giving the maximum chiral resolution of enantiomers.
Keywords: Enantioseparation; Single-isomer β-cyclodextrin; Capillary electrophoresis; 6-Mono (alkylimidazolium)-β-cyclodextrin
Effect of alkylimidazolium substituents on enantioseparation ability of single-isomer alkylimidazolium-β-cyclodextrin derivatives in capillary electrophoresis by Weihua Tang; Teng-Teng Ong; I. Wayan Muderawan; Siu Choon Ng (pp. 227-233).
A family of 6-mono(3-alkylimidazolium)-β-cyclodextrins with one primary hydroxyl group replaced by an alkylimidazolium cation has been developed. The effect of alkyl substitutents on the enantioresolution ability of these single-isomer cyclodextrins towards dansyl amino acids has been studied by capillary electrophoresis. Systematical investigations on the effect of buffer pH and selector concentration on the enatioseparation show that chiral selectors with a shorter alkyl chain (R=C nH2 n+1, n≤4) presented more powerful chiral recognition ability. These newly introduced single-isomer β-cyclodextrin derivatives proved to be effective chiral selectors for most selected dansyl amino acids at low buffer pH (e.g. pH 5.0) with selector concentration no less than 3mM. The apparent complex stability constants between alkylimidazolium β-CDs and dansyl amino acids were also theoretically determined by using the mobility difference model proposed by Wren and Rowe. The side alkyl chains from both dansyl amino acids and alkylimidazolium β-CDs displayed significant effect on the apparent complex stability constants. Both the optimum selector concentrations calculated according to the model, however, were much lower than the experimental values giving the maximum chiral resolution of enantiomers.
Keywords: Enantioseparation; Single-isomer β-cyclodextrin; Capillary electrophoresis; 6-Mono (alkylimidazolium)-β-cyclodextrin
Methods for extracting biochemical information from bacterial Raman spectra: An explorative study on Cupriavidus metallidurans by Joke De Gelder; Kris De Gussem; Peter Vandenabeele; Paul De Vos; Luc Moens (pp. 234-240).
In this study, we explore Raman spectra of bacteria for their biochemical information. Therefore, a database of biomolecules was used and several approaches were applied such as the study of difference spectra, the calculation dot products, the usage of coefficients obtained from an EMSC procedure and the application of 2D correlation spectroscopy. These methods were applied on a dataset containing Raman spectra of Cupriavidus metallidurans LMG 1195 in five stages of its growth, aiming to extract information about the evolution of cell components during growth. EMSC coefficients seemed to be most promising for tracking metabolic products and the results were often confirmed by difference spectra or by 2D correlation spectroscopy.
Keywords: Raman spectroscopy; Bacteria; Cupriavidus metallidurans; EMSC; Metabolism; 2D correlation spectroscopy
Methods for extracting biochemical information from bacterial Raman spectra: An explorative study on Cupriavidus metallidurans by Joke De Gelder; Kris De Gussem; Peter Vandenabeele; Paul De Vos; Luc Moens (pp. 234-240).
In this study, we explore Raman spectra of bacteria for their biochemical information. Therefore, a database of biomolecules was used and several approaches were applied such as the study of difference spectra, the calculation dot products, the usage of coefficients obtained from an EMSC procedure and the application of 2D correlation spectroscopy. These methods were applied on a dataset containing Raman spectra of Cupriavidus metallidurans LMG 1195 in five stages of its growth, aiming to extract information about the evolution of cell components during growth. EMSC coefficients seemed to be most promising for tracking metabolic products and the results were often confirmed by difference spectra or by 2D correlation spectroscopy.
Keywords: Raman spectroscopy; Bacteria; Cupriavidus metallidurans; EMSC; Metabolism; 2D correlation spectroscopy
The detection of laser-induced structural change of MnO2 using in situ Raman spectroscopy combined with self-modeling curve resolution technique by Effendi Widjaja; Jeyagowry T. Sampanthar (pp. 241-245).
In this paper, we present the use of one of the self-modeling curve resolution techniques, band-target entropy minimization (BTEM), which is independent of any spectral library, to elucidate Raman pure component spectra of two different manganese oxides arising from laser-induced structural changes. It is often extremely difficult to obtain the pure Raman spectrum of MnO2 without changing it to another structural form. However, using BTEM to analyze the collected in situ Raman spectra measured as a function of laser exposure time, has enabled us to obtain both the pure component spectra of the original sample and the product due to laser irradiation. This technique proves to be an efficient Raman spectral interpretation method for thermal sensitive solid samples.
Keywords: In situ Raman spectroscopy; Laser irradiation; Self-modeling curve resolution; Band-target entropy minimization (BTEM)
The detection of laser-induced structural change of MnO2 using in situ Raman spectroscopy combined with self-modeling curve resolution technique by Effendi Widjaja; Jeyagowry T. Sampanthar (pp. 241-245).
In this paper, we present the use of one of the self-modeling curve resolution techniques, band-target entropy minimization (BTEM), which is independent of any spectral library, to elucidate Raman pure component spectra of two different manganese oxides arising from laser-induced structural changes. It is often extremely difficult to obtain the pure Raman spectrum of MnO2 without changing it to another structural form. However, using BTEM to analyze the collected in situ Raman spectra measured as a function of laser exposure time, has enabled us to obtain both the pure component spectra of the original sample and the product due to laser irradiation. This technique proves to be an efficient Raman spectral interpretation method for thermal sensitive solid samples.
Keywords: In situ Raman spectroscopy; Laser irradiation; Self-modeling curve resolution; Band-target entropy minimization (BTEM)
Simultaneous determination of glycerol and clavulanic acid in an antibiotic bioprocess using attenuated total reflectance mid infrared spectroscopy by Payal Roychoudhury; Brian McNeil; Linda M. Harvey (pp. 246-252).
Attenuated total reflectance mid infrared (ATR-MIR) spectroscopy is a potential technique for the near real-time monitoring of filamentous bioprocesses. Here we investigate the utility of ATR-MIR to monitor and predict concentrations of glycerol and product (clavulanic acid) in a complex antibiotic bioprocess. Streptomyces clavuligerus exhibits filamentous growth, thus, as biomass accumulates the process fluid becomes much more viscous, and develops pronounced non-Newtonian behaviour. A multivariate statistical technique, partial least square (PLS) has been used to develop models for the key analytes over the time course of the bioprocess. These models were then validated externally using unseen samples, not used in the original modelling exercise. Despite the heterogeneous nature of the bioprocess and the resulting complexity of the spectra, the models developed had high correlation coefficient values and low prediction error values of 0.302 and 0.009 for glycerol and clavulanic acid, respectively. The findings extend the use of ATR-MIR in these difficult fluids which are typical of filamentous industrial bioprocesses, and demonstrate the practical utility of the technique in the measurement of a range of analyte types, including those present at relatively modest levels compared to the concentrations of biomass and major substrates.
Keywords: Attenuated total reflectance mid infrared spectroscopy; Streptomyces; Multivariate statistical technique; Partial least square
Simultaneous determination of glycerol and clavulanic acid in an antibiotic bioprocess using attenuated total reflectance mid infrared spectroscopy by Payal Roychoudhury; Brian McNeil; Linda M. Harvey (pp. 246-252).
Attenuated total reflectance mid infrared (ATR-MIR) spectroscopy is a potential technique for the near real-time monitoring of filamentous bioprocesses. Here we investigate the utility of ATR-MIR to monitor and predict concentrations of glycerol and product (clavulanic acid) in a complex antibiotic bioprocess. Streptomyces clavuligerus exhibits filamentous growth, thus, as biomass accumulates the process fluid becomes much more viscous, and develops pronounced non-Newtonian behaviour. A multivariate statistical technique, partial least square (PLS) has been used to develop models for the key analytes over the time course of the bioprocess. These models were then validated externally using unseen samples, not used in the original modelling exercise. Despite the heterogeneous nature of the bioprocess and the resulting complexity of the spectra, the models developed had high correlation coefficient values and low prediction error values of 0.302 and 0.009 for glycerol and clavulanic acid, respectively. The findings extend the use of ATR-MIR in these difficult fluids which are typical of filamentous industrial bioprocesses, and demonstrate the practical utility of the technique in the measurement of a range of analyte types, including those present at relatively modest levels compared to the concentrations of biomass and major substrates.
Keywords: Attenuated total reflectance mid infrared spectroscopy; Streptomyces; Multivariate statistical technique; Partial least square
Selecting the optimum number of partial least squares components for the calibration of attenuated total reflectance-mid-infrared spectra of undesigned kerosene samples by M.P. Gómez-Carracedo; J.M. Andrade; D.N. Rutledge; N.M. Faber (pp. 253-265).
Selecting the correct dimensionality is critical for obtaining partial least squares (PLS) regression models with good predictive ability. Although calibration and validation sets are best established using experimental designs, industrial laboratories cannot afford such an approach. Typically, samples are collected in an (formally) undesigned way, spread over time and their measurements are included in routine measurement processes. This makes it hard to evaluate PLS model dimensionality. In this paper, classical criteria (leave-one-out cross-validation and adjusted Wold's criterion) are compared to recently proposed alternatives (smoothed PLS–PoLiSh and a randomization test) to seek out the optimum dimensionality of PLS models. Kerosene (jet fuel) samples were measured by attenuated total reflectance-mid-IR spectrometry and their spectra where used to predict eight important properties determined using reference methods that are time-consuming and prone to analytical errors. The alternative methods were shown to give reliable dimensionality predictions when compared to external validation. By contrast, the simpler methods seemed to be largely affected by the largest changes in the modeling capabilities of the first components.
Keywords: Partial least squares dimensionality; Cross-validation; Smoothed partial least squares; Randomization test; Kerosene; Infrared spectrometry
Selecting the optimum number of partial least squares components for the calibration of attenuated total reflectance-mid-infrared spectra of undesigned kerosene samples by M.P. Gómez-Carracedo; J.M. Andrade; D.N. Rutledge; N.M. Faber (pp. 253-265).
Selecting the correct dimensionality is critical for obtaining partial least squares (PLS) regression models with good predictive ability. Although calibration and validation sets are best established using experimental designs, industrial laboratories cannot afford such an approach. Typically, samples are collected in an (formally) undesigned way, spread over time and their measurements are included in routine measurement processes. This makes it hard to evaluate PLS model dimensionality. In this paper, classical criteria (leave-one-out cross-validation and adjusted Wold's criterion) are compared to recently proposed alternatives (smoothed PLS–PoLiSh and a randomization test) to seek out the optimum dimensionality of PLS models. Kerosene (jet fuel) samples were measured by attenuated total reflectance-mid-IR spectrometry and their spectra where used to predict eight important properties determined using reference methods that are time-consuming and prone to analytical errors. The alternative methods were shown to give reliable dimensionality predictions when compared to external validation. By contrast, the simpler methods seemed to be largely affected by the largest changes in the modeling capabilities of the first components.
Keywords: Partial least squares dimensionality; Cross-validation; Smoothed partial least squares; Randomization test; Kerosene; Infrared spectrometry
Mixture resolution according to the percentage of robusta variety in order to detect adulteration in roasted coffee by near infrared spectroscopy by C. Pizarro; I. Esteban-Díez; J.M. González-Sáiz (pp. 266-276).
Near infrared spectroscopy (NIRS), combined with multivariate calibration methods, has been used to quantify the robusta variety content of roasted coffee samples, as a means for controlling and avoiding coffee adulteration, which is a very important issue taking into account the great variability of the final sale price depending on coffee varietal origin. In pursuit of this aim, PLS regression and a wavelet-based pre-processing method that we have recently developed called OWAVEC were applied, in order to simultaneously operate two crucial pre-processing steps in multivariate calibration: signal correction and data compression. Several pre-processing methods (mean centering, first derivative and two orthogonal signal correction methods, OSC and DOSC) were additionally applied in order to find calibration models with as best a predictive ability as possible and to evaluate the performance of the OWAVEC method, comparing the respective quality of the different regression models constructed. The calibration model developed after pre-processing derivative spectra by OWAVEC provided high quality results (0.79% RMSEP), the percentage of robusta variety being predicted with a reliability notably better than that associated with the models constructed from raw spectra and also from data corrected by other orthogonal signal correction methods, and showing a higher model simplicity.
Keywords: Near infrared spectroscopy; Multivariate calibration; Orthogonal wavelet correction; Wavelet transform; Genetic algorithms; Orthogonal signal correction; Coffee authenticity
Mixture resolution according to the percentage of robusta variety in order to detect adulteration in roasted coffee by near infrared spectroscopy by C. Pizarro; I. Esteban-Díez; J.M. González-Sáiz (pp. 266-276).
Near infrared spectroscopy (NIRS), combined with multivariate calibration methods, has been used to quantify the robusta variety content of roasted coffee samples, as a means for controlling and avoiding coffee adulteration, which is a very important issue taking into account the great variability of the final sale price depending on coffee varietal origin. In pursuit of this aim, PLS regression and a wavelet-based pre-processing method that we have recently developed called OWAVEC were applied, in order to simultaneously operate two crucial pre-processing steps in multivariate calibration: signal correction and data compression. Several pre-processing methods (mean centering, first derivative and two orthogonal signal correction methods, OSC and DOSC) were additionally applied in order to find calibration models with as best a predictive ability as possible and to evaluate the performance of the OWAVEC method, comparing the respective quality of the different regression models constructed. The calibration model developed after pre-processing derivative spectra by OWAVEC provided high quality results (0.79% RMSEP), the percentage of robusta variety being predicted with a reliability notably better than that associated with the models constructed from raw spectra and also from data corrected by other orthogonal signal correction methods, and showing a higher model simplicity.
Keywords: Near infrared spectroscopy; Multivariate calibration; Orthogonal wavelet correction; Wavelet transform; Genetic algorithms; Orthogonal signal correction; Coffee authenticity
Validation of the concentration profiles obtained from the near infrared/multivariate curve resolution monitoring of reactions of epoxy resins using high performance liquid chromatography as a reference method by M. Garrido; M.S. Larrechi; F.X. Rius (pp. 277-285).
This paper reports the validation of the results obtained by combining near infrared spectroscopy and multivariate curve resolution-alternating least squares (MCR-ALS) and using high performance liquid chromatography as a reference method, for the model reaction of phenylglycidylether (PGE) and aniline. The results are obtained as concentration profiles over the reaction time. The trueness of the proposed method has been evaluated in terms of lack of bias. The joint test for the intercept and the slope showed that there were no significant differences between the profiles calculated spectroscopically and the ones obtained experimentally by means of the chromatographic reference method at an overall level of confidence of 5%. The uncertainty of the results was estimated by using information derived from the process of assessment of trueness. Such operational aspects as the cost and availability of instrumentation and the length and cost of the analysis were evaluated. The method proposed is a good way of monitoring the reactions of epoxy resins, and it adequately shows how the species concentration varies over time.
Keywords: Validation; Multivariate curve resolution; Alternating least squares; Epoxy resins; High performance liquid chromatography (HPLC)
Validation of the concentration profiles obtained from the near infrared/multivariate curve resolution monitoring of reactions of epoxy resins using high performance liquid chromatography as a reference method by M. Garrido; M.S. Larrechi; F.X. Rius (pp. 277-285).
This paper reports the validation of the results obtained by combining near infrared spectroscopy and multivariate curve resolution-alternating least squares (MCR-ALS) and using high performance liquid chromatography as a reference method, for the model reaction of phenylglycidylether (PGE) and aniline. The results are obtained as concentration profiles over the reaction time. The trueness of the proposed method has been evaluated in terms of lack of bias. The joint test for the intercept and the slope showed that there were no significant differences between the profiles calculated spectroscopically and the ones obtained experimentally by means of the chromatographic reference method at an overall level of confidence of 5%. The uncertainty of the results was estimated by using information derived from the process of assessment of trueness. Such operational aspects as the cost and availability of instrumentation and the length and cost of the analysis were evaluated. The method proposed is a good way of monitoring the reactions of epoxy resins, and it adequately shows how the species concentration varies over time.
Keywords: Validation; Multivariate curve resolution; Alternating least squares; Epoxy resins; High performance liquid chromatography (HPLC)
A new liquid-phase microextraction method based on solidification of floating organic drop by Mohammad Reza Khalili Zanjani; Yadollah Yamini; Shahab Shariati; Jan Åke Jönsson (pp. 286-293).
In the present study, a new and versatile liquid-phase microextraction method is described. This method requires very simple and cheap apparatus and also a small amount of organic solvent. Eight microliters of 1-undecanol was delivered to the surface of solution containing analytes and solution was stirred for a desired time. Then sample vial was cooled by inserting it into an ice bath for 5min. The solidified 1-undecanol was transferred into a suitable vial and immediately melted; then, 2μL of it was injected into a gas chromatograph for analysis.Some polycyclic aromatic hydrocarbons (PAHs) were used as model compounds for developing and evaluating of the method performance. Analysis was carried out by gas chromatography/flame ionization detection (GC/FID).Several factors influencing the microextraction efficiency, such as the nature and volume of organic solvent, the temperature and volume of sample solution, stirring rate and extraction time were investigated and optimized. The applicability of the technique was evaluated by determination of trace amounts of PAHs in environmental samples. Under the optimized conditions, the detection limits (LOD) of the method were in the range of 0.07–1.67μgL−1 and relative standard deviations (R.S.D.) for 10μgL−1 PAHs were <7%. A good linearity ( r2>0.995) in a calibration range of 0.25–300.00μgL−1 was obtained. After 30min extraction duration, enrichment factors were in the range of 594–1940. Finally, the proposed method was applied to the determination of trace amounts of PAHs in several real water samples, and satisfactory results were resulted. Since very simple devices were used, this new technique is affordable, efficient, and convenient for extraction and determination of low concentrations of PAHs in water samples.
Keywords: Liquid-phase microextraction; Water analysis; Gas chromatography-flame ionization detection; Polycyclic aromatic hydrocarbons
A new liquid-phase microextraction method based on solidification of floating organic drop by Mohammad Reza Khalili Zanjani; Yadollah Yamini; Shahab Shariati; Jan Åke Jönsson (pp. 286-293).
In the present study, a new and versatile liquid-phase microextraction method is described. This method requires very simple and cheap apparatus and also a small amount of organic solvent. Eight microliters of 1-undecanol was delivered to the surface of solution containing analytes and solution was stirred for a desired time. Then sample vial was cooled by inserting it into an ice bath for 5min. The solidified 1-undecanol was transferred into a suitable vial and immediately melted; then, 2μL of it was injected into a gas chromatograph for analysis.Some polycyclic aromatic hydrocarbons (PAHs) were used as model compounds for developing and evaluating of the method performance. Analysis was carried out by gas chromatography/flame ionization detection (GC/FID).Several factors influencing the microextraction efficiency, such as the nature and volume of organic solvent, the temperature and volume of sample solution, stirring rate and extraction time were investigated and optimized. The applicability of the technique was evaluated by determination of trace amounts of PAHs in environmental samples. Under the optimized conditions, the detection limits (LOD) of the method were in the range of 0.07–1.67μgL−1 and relative standard deviations (R.S.D.) for 10μgL−1 PAHs were <7%. A good linearity ( r2>0.995) in a calibration range of 0.25–300.00μgL−1 was obtained. After 30min extraction duration, enrichment factors were in the range of 594–1940. Finally, the proposed method was applied to the determination of trace amounts of PAHs in several real water samples, and satisfactory results were resulted. Since very simple devices were used, this new technique is affordable, efficient, and convenient for extraction and determination of low concentrations of PAHs in water samples.
Keywords: Liquid-phase microextraction; Water analysis; Gas chromatography-flame ionization detection; Polycyclic aromatic hydrocarbons
Continuous-flow microextraction and gas chromatographic–mass spectrometric determination of polycyclic aromatic hydrocarbon compounds in water by Yan Liu; Yuki Hashi; Jin-Ming Lin (pp. 294-299).
A new method of the determination polycyclic aromatic hydrocarbons (PAHs) in water samples was developed by continuous-flow microextraction (CFME) coupled with gas chromatography–mass spectrometry (GC–MS). In this experiment, 15mL sample solution with no salt-added was flowed at the rate of 1.0mLmin−1 through 3μL benzene as extraction solvent. Under the optimal extraction conditions, the developed method was found to yield a linear calibration curve in the concentration range from 0.05 to 15ngmL−1. Furthermore, the accuracy and repeatability of the method were good by calculating from water samples spiked at known concentrations of PAHs, and the recovery of optimal method was satisfactory. The results showed that CFME was an efficient preconcentration method for extraction of PAHs from spiked water samples.
Keywords: Continuous-flow microextraction; Polycyclic aromatic hydrocarbons; Gas chromatography–mass spectrometry; Water analysis
Continuous-flow microextraction and gas chromatographic–mass spectrometric determination of polycyclic aromatic hydrocarbon compounds in water by Yan Liu; Yuki Hashi; Jin-Ming Lin (pp. 294-299).
A new method of the determination polycyclic aromatic hydrocarbons (PAHs) in water samples was developed by continuous-flow microextraction (CFME) coupled with gas chromatography–mass spectrometry (GC–MS). In this experiment, 15mL sample solution with no salt-added was flowed at the rate of 1.0mLmin−1 through 3μL benzene as extraction solvent. Under the optimal extraction conditions, the developed method was found to yield a linear calibration curve in the concentration range from 0.05 to 15ngmL−1. Furthermore, the accuracy and repeatability of the method were good by calculating from water samples spiked at known concentrations of PAHs, and the recovery of optimal method was satisfactory. The results showed that CFME was an efficient preconcentration method for extraction of PAHs from spiked water samples.
Keywords: Continuous-flow microextraction; Polycyclic aromatic hydrocarbons; Gas chromatography–mass spectrometry; Water analysis
Determination of antimony(III) and total antimony by single-drop microextraction combined with electrothermal atomic absorption spectrometry by Zhefeng Fan (pp. 300-304).
A simple and sensitive method for using electrothermal atomic absorption spectrometry (ET AAS) with Rh as permanent modifier determination of Sb(III) and total Sb after separation and preconcentration by N-benzoyl- N-phenylhydroxylamine (BPHA)–chloroform single drop has been developed. Parameters, such as pyrolysis and atomization temperature, solvent type, pH, BPHA concentration, extraction time, drop size, stirring rate and sample volume were investigated. Under the optimized experimental conditions, the detection limits (3 σ) were 8.0ngL−1 for Sb(III) and 9.2ngL−1 for total Sb, respectively. The relative standard deviations (R.S.Ds.) were 6.6% for Sb(III) and 7.1% for total Sb ( c=0.2ngmL−1, n=7), respectively. The enrichment factor was 96. The developed method has been applied successfully to the determination of Sb(III) and total Sb in natural water samples.
Keywords: Single-drop microextraction; Electrothermal atomic absorption spectrometry; Antimony species; Permanent modifier
Determination of antimony(III) and total antimony by single-drop microextraction combined with electrothermal atomic absorption spectrometry by Zhefeng Fan (pp. 300-304).
A simple and sensitive method for using electrothermal atomic absorption spectrometry (ET AAS) with Rh as permanent modifier determination of Sb(III) and total Sb after separation and preconcentration by N-benzoyl- N-phenylhydroxylamine (BPHA)–chloroform single drop has been developed. Parameters, such as pyrolysis and atomization temperature, solvent type, pH, BPHA concentration, extraction time, drop size, stirring rate and sample volume were investigated. Under the optimized experimental conditions, the detection limits (3 σ) were 8.0ngL−1 for Sb(III) and 9.2ngL−1 for total Sb, respectively. The relative standard deviations (R.S.Ds.) were 6.6% for Sb(III) and 7.1% for total Sb ( c=0.2ngmL−1, n=7), respectively. The enrichment factor was 96. The developed method has been applied successfully to the determination of Sb(III) and total Sb in natural water samples.
Keywords: Single-drop microextraction; Electrothermal atomic absorption spectrometry; Antimony species; Permanent modifier
Dispersive liquid–liquid microextraction combined with graphite furnace atomic absorption spectrometry by Elham Zeini Jahromi; Araz Bidari; Yaghoub Assadi; Mohammad Reza Milani Hosseini; Mohammad Reza Jamali (pp. 305-311).
Dispersive liquid–liquid microextraction (DLLME) technique was successfully used as a sample preparation method for graphite furnace atomic absorption spectrometry (GF AAS). In this extraction method, 500μL methanol (disperser solvent) containing 34μL carbon tetrachloride (extraction solvent) and 0.00010g ammonium pyrrolidine dithiocarbamate (chelating agent) was rapidly injected by syringe into the water sample containing cadmium ions (interest analyte). Thereby, a cloudy solution formed. The cloudy state resulted from the formation of fine droplets of carbon tetrachloride, which have been dispersed, in bulk aqueous sample. At this stage, cadmium reacts with ammonium pyrrolidine dithiocarbamate, and therefore, hydrophobic complex forms which is extracted into the fine droplets of carbon tetrachloride. After centrifugation (2min at 5000rpm), these droplets were sedimented at the bottom of the conical test tube (25±1μL). Then a 20μL of sedimented phase containing enriched analyte was determined by GF AAS.Some effective parameters on extraction and complex formation, such as extraction and disperser solvent type and their volume, extraction time, salt effect, pH and concentration of the chelating agent have been optimized. Under the optimum conditions, the enrichment factor 125 was obtained from only 5.00mL of water sample. The calibration graph was linear in the rage of 2–20ngL−1 with detection limit of 0.6ngL−1. The relative standard deviation (R.S.D.s) for ten replicate measurements of 20ngL−1 of cadmium was 3.5%. The relative recoveries of cadmium in tap, sea and rivers water samples at spiking level of 5 and 10ngL−1 are 108, 95, 87 and 98%, respectively. The characteristics of the proposed method have been compared with cloud point extraction (CPE), on-line liquid–liquid extraction, single drop microextraction (SDME), on-line solid phase extraction (SPE) and co-precipitation based on bibliographic data. Therefore, DLLME combined with GF AAS is a very simple, rapid and sensitive method, which requires low volume of sample (5.00mL).
Keywords: Dispersive liquid–liquid microextraction; Preconcentration; Cadmium; Graphite furnace atomic absorption spectrometry; Water analysis
Dispersive liquid–liquid microextraction combined with graphite furnace atomic absorption spectrometry by Elham Zeini Jahromi; Araz Bidari; Yaghoub Assadi; Mohammad Reza Milani Hosseini; Mohammad Reza Jamali (pp. 305-311).
Dispersive liquid–liquid microextraction (DLLME) technique was successfully used as a sample preparation method for graphite furnace atomic absorption spectrometry (GF AAS). In this extraction method, 500μL methanol (disperser solvent) containing 34μL carbon tetrachloride (extraction solvent) and 0.00010g ammonium pyrrolidine dithiocarbamate (chelating agent) was rapidly injected by syringe into the water sample containing cadmium ions (interest analyte). Thereby, a cloudy solution formed. The cloudy state resulted from the formation of fine droplets of carbon tetrachloride, which have been dispersed, in bulk aqueous sample. At this stage, cadmium reacts with ammonium pyrrolidine dithiocarbamate, and therefore, hydrophobic complex forms which is extracted into the fine droplets of carbon tetrachloride. After centrifugation (2min at 5000rpm), these droplets were sedimented at the bottom of the conical test tube (25±1μL). Then a 20μL of sedimented phase containing enriched analyte was determined by GF AAS.Some effective parameters on extraction and complex formation, such as extraction and disperser solvent type and their volume, extraction time, salt effect, pH and concentration of the chelating agent have been optimized. Under the optimum conditions, the enrichment factor 125 was obtained from only 5.00mL of water sample. The calibration graph was linear in the rage of 2–20ngL−1 with detection limit of 0.6ngL−1. The relative standard deviation (R.S.D.s) for ten replicate measurements of 20ngL−1 of cadmium was 3.5%. The relative recoveries of cadmium in tap, sea and rivers water samples at spiking level of 5 and 10ngL−1 are 108, 95, 87 and 98%, respectively. The characteristics of the proposed method have been compared with cloud point extraction (CPE), on-line liquid–liquid extraction, single drop microextraction (SDME), on-line solid phase extraction (SPE) and co-precipitation based on bibliographic data. Therefore, DLLME combined with GF AAS is a very simple, rapid and sensitive method, which requires low volume of sample (5.00mL).
Keywords: Dispersive liquid–liquid microextraction; Preconcentration; Cadmium; Graphite furnace atomic absorption spectrometry; Water analysis
Inorganic arsenic speciation in water and seawater by anodic stripping voltammetry with a gold microelectrode by Pascal Salaün; Britta Planer-Friedrich; Constant M.G. van den Berg (pp. 312-322).
The determination of arsenic in sea and freshwater by anodic stripping voltammetry (ASV) was revisited because of problems related to unstable peaks and inconveniently strong acidic conditions used by existing methods. Contrary to previous work it was found, that As(III) can be determined by ASV using a gold microwire electrode at any pH including the neutral pH typical for natural waters. As(V) on the other hand, requires acidification to pH 1, but this is still a much milder condition than used previously. This is the basis of a new method for the chemical speciation of arsenic in natural waters. The limits of detection are 0.2nM As(III) at pH 8 and 0.3nM combined arsenic (III+V) at pH 1 with a 30s deposition time. These limits are lowered by extending the deposition time. The detection step at pH 8 was stripping chronopotentiometry (SC) as this was found to give a lower detection limit than ASV. Copper is co-determined simultaneously with arsenic. The method was applied successfully to the determination of arsenic as well as copper in samples from the Irish Sea, mineral water and tap water.
Keywords: Arsenic; Speciation; Seawater; Anodic stripping voltammetry; Microelectrode; Microwire electrode
Inorganic arsenic speciation in water and seawater by anodic stripping voltammetry with a gold microelectrode by Pascal Salaün; Britta Planer-Friedrich; Constant M.G. van den Berg (pp. 312-322).
The determination of arsenic in sea and freshwater by anodic stripping voltammetry (ASV) was revisited because of problems related to unstable peaks and inconveniently strong acidic conditions used by existing methods. Contrary to previous work it was found, that As(III) can be determined by ASV using a gold microwire electrode at any pH including the neutral pH typical for natural waters. As(V) on the other hand, requires acidification to pH 1, but this is still a much milder condition than used previously. This is the basis of a new method for the chemical speciation of arsenic in natural waters. The limits of detection are 0.2nM As(III) at pH 8 and 0.3nM combined arsenic (III+V) at pH 1 with a 30s deposition time. These limits are lowered by extending the deposition time. The detection step at pH 8 was stripping chronopotentiometry (SC) as this was found to give a lower detection limit than ASV. Copper is co-determined simultaneously with arsenic. The method was applied successfully to the determination of arsenic as well as copper in samples from the Irish Sea, mineral water and tap water.
Keywords: Arsenic; Speciation; Seawater; Anodic stripping voltammetry; Microelectrode; Microwire electrode
Determination of β-carboline alkaloids in foods and beverages by high-performance liquid chromatography with electrochemical detection at a glassy carbon electrode modified with carbon nanotubes by Lourdes Agüí; Carlos Peña-Farfal; Paloma Yáñez-Sedeño; José M. Pingarrón (pp. 323-330).
Simple and sensitive methods for the separation and quantification of β-carboline alkaloids in foods and beverages by HPLC with electrochemical detection at carbon nanotubes–modified glassy carbon electrodes (CNTs–GCE) are reported. Electrode modification with multi-wall CNTs produced an improved amperometric response to β-carbolines, in spite of the working medium consisting of methanol:acetonitrile: 0.05molL−1 Na2HPO4 solution of pH 9.0 (20:20:60). On the contrary to that observed at a bare GCE, a good repeatability of the amperometric measurements carried out at +900mV versus Ag/AgCl (R.S.D. of 3.2% for ip, n=20) was achieved at the CNTs–GCE. Using an Ultrabase C18 column and isocratic elution with the above mentioned mobile phase, a complete resolution of the chromatographic peaks for harmalol, harmaline, norharmane, harmane and harmine, was achieved. Calibration graphs over the 0.25–100μM range with detection limits ranging between 4 and 19ngmL−1, were obtained. The HPLC–ED at CNTs–GCE method was applied to the analysis of beer, coffee and cheese samples, spiked with β-carbolines at concentration levels corresponding to those may be found in the respective samples. The steps involved in sample treatment, such as extraction and clean-up, were optimized for each type of sample. Recoveries ranging between 92 and 102% for beer, 92 and 101% for coffee, and 88 and 100% for cheese, at sub-μgmL−1 or g−1 analytes concentration levels were achieved.
Keywords: β-Carboline alkaloids; Liquid chromatography; Amperometric detection; Carbon natotubes modified electrodes; Food
Determination of β-carboline alkaloids in foods and beverages by high-performance liquid chromatography with electrochemical detection at a glassy carbon electrode modified with carbon nanotubes by Lourdes Agüí; Carlos Peña-Farfal; Paloma Yáñez-Sedeño; José M. Pingarrón (pp. 323-330).
Simple and sensitive methods for the separation and quantification of β-carboline alkaloids in foods and beverages by HPLC with electrochemical detection at carbon nanotubes–modified glassy carbon electrodes (CNTs–GCE) are reported. Electrode modification with multi-wall CNTs produced an improved amperometric response to β-carbolines, in spite of the working medium consisting of methanol:acetonitrile: 0.05molL−1 Na2HPO4 solution of pH 9.0 (20:20:60). On the contrary to that observed at a bare GCE, a good repeatability of the amperometric measurements carried out at +900mV versus Ag/AgCl (R.S.D. of 3.2% for ip, n=20) was achieved at the CNTs–GCE. Using an Ultrabase C18 column and isocratic elution with the above mentioned mobile phase, a complete resolution of the chromatographic peaks for harmalol, harmaline, norharmane, harmane and harmine, was achieved. Calibration graphs over the 0.25–100μM range with detection limits ranging between 4 and 19ngmL−1, were obtained. The HPLC–ED at CNTs–GCE method was applied to the analysis of beer, coffee and cheese samples, spiked with β-carbolines at concentration levels corresponding to those may be found in the respective samples. The steps involved in sample treatment, such as extraction and clean-up, were optimized for each type of sample. Recoveries ranging between 92 and 102% for beer, 92 and 101% for coffee, and 88 and 100% for cheese, at sub-μgmL−1 or g−1 analytes concentration levels were achieved.
Keywords: β-Carboline alkaloids; Liquid chromatography; Amperometric detection; Carbon natotubes modified electrodes; Food
Determination of trace thiocyanate with nano-silver coated multi-walled carbon nanotubes modified glassy carbon electrode by Pinghua Yang; Wanzhi Wei; Chunyuan Tao (pp. 331-336).
Novel nano-silver coated multi-walled carbon nanotube composites were prepared and used to fabricate a modified electrode. The application of the nano-silver coated multi-walled carbon nanotube composites modified electrode for determination of trace thiocyanate is demonstrated for the first time. The influence of substrate, pH and interference of coexisting substances was investigated for response properties of the electrode. There was a linear relationship at the range 2.5×10−9 to 5×10−8molL−1 and 5×10−8 to 1×10−6molL−1 of thiocyanate with the decrement of anodic DPV peak currents. The limit of detection was 1×10−9molL−1(S/N=3). The constructed electrode showed excellent reproducibility and stability. Actual urine and saliva samples of smoker and non-smoker were analyzed and satisfactory results were obtained. This method provides a new way to construct any electrode for biological and environmental analysis.
Keywords: Nano-silver coated multi-walled carbon nanotubes; Thiocyanate; Modified electrode; Determination
Determination of trace thiocyanate with nano-silver coated multi-walled carbon nanotubes modified glassy carbon electrode by Pinghua Yang; Wanzhi Wei; Chunyuan Tao (pp. 331-336).
Novel nano-silver coated multi-walled carbon nanotube composites were prepared and used to fabricate a modified electrode. The application of the nano-silver coated multi-walled carbon nanotube composites modified electrode for determination of trace thiocyanate is demonstrated for the first time. The influence of substrate, pH and interference of coexisting substances was investigated for response properties of the electrode. There was a linear relationship at the range 2.5×10−9 to 5×10−8molL−1 and 5×10−8 to 1×10−6molL−1 of thiocyanate with the decrement of anodic DPV peak currents. The limit of detection was 1×10−9molL−1(S/N=3). The constructed electrode showed excellent reproducibility and stability. Actual urine and saliva samples of smoker and non-smoker were analyzed and satisfactory results were obtained. This method provides a new way to construct any electrode for biological and environmental analysis.
Keywords: Nano-silver coated multi-walled carbon nanotubes; Thiocyanate; Modified electrode; Determination
A quercetin-modified biosensor for amperometric determination of uric acid in the presence of ascorbic acid by Jian-Bo He; Guan-Ping Jin; Qun-Zhi Chen; Yan Wang (pp. 337-343).
The present work reports a quercetin-modified wax-impregnated graphite electrode (Qu/WGE) prepared through an electrochemical oxidation procedure in quercetin-containing phosphate buffer solution (PBS), for the purpose of detecting uric acid (UA) in the presence of ascorbic acid (AA). During modification quercetin was oxidized to the corresponding quinonic structure, and in the blank buffer solution the electrodeposited film exhibits a voltammetric response anticipated for the surface-immobilized quercetin. Retarding effect of the film towards the reaction of anionic species was found; therefore the pH of sample solutions was selected to ensure the analyte in molecular form. At suitable pHs the Qu/WGE shows excellent electrocatalytic effect towards the oxidation of both AA and UA, and separates the voltammetric signal of UA from AA by about 280mV, allowing simultaneous detection of these two species. A linear relation between the peak current and concentration was obtained for UA in the range of 1–50μM in the presence of 0.5mM AA, with a detection limit 1.0μM ( S/ N=3). This sensor was stable, reproducible and outstanding for long-term use.
Keywords: Quercetin-modified electrode; Uric acid; Ascorbic acid; Biosensor; Spectroelectrochemistry
A quercetin-modified biosensor for amperometric determination of uric acid in the presence of ascorbic acid by Jian-Bo He; Guan-Ping Jin; Qun-Zhi Chen; Yan Wang (pp. 337-343).
The present work reports a quercetin-modified wax-impregnated graphite electrode (Qu/WGE) prepared through an electrochemical oxidation procedure in quercetin-containing phosphate buffer solution (PBS), for the purpose of detecting uric acid (UA) in the presence of ascorbic acid (AA). During modification quercetin was oxidized to the corresponding quinonic structure, and in the blank buffer solution the electrodeposited film exhibits a voltammetric response anticipated for the surface-immobilized quercetin. Retarding effect of the film towards the reaction of anionic species was found; therefore the pH of sample solutions was selected to ensure the analyte in molecular form. At suitable pHs the Qu/WGE shows excellent electrocatalytic effect towards the oxidation of both AA and UA, and separates the voltammetric signal of UA from AA by about 280mV, allowing simultaneous detection of these two species. A linear relation between the peak current and concentration was obtained for UA in the range of 1–50μM in the presence of 0.5mM AA, with a detection limit 1.0μM ( S/ N=3). This sensor was stable, reproducible and outstanding for long-term use.
Keywords: Quercetin-modified electrode; Uric acid; Ascorbic acid; Biosensor; Spectroelectrochemistry
Development of a peptide inhibitor-based cantilever sensor assay for cyclic adenosine monophosphate-dependent protein kinase by Hyuk-Sung Kwon; Ki-Cheol Han; Kyo Seon Hwang; Jeong Hoon Lee; Tae Song Kim; Dae Sung Yoon; Eun Gyeong Yang (pp. 344-349).
A highly sensitive nanomechanical cantilever sensor assay based on an electrical measurement has been developed for detecting activated cyclic adenosine monophosphate (cyclic AMP)-dependent protein kinase (PKA). Employing a peptide derived from the heat-stable protein kinase inhibitor (PKI), a magnetic bead system was first selected as a vehicle to immobilize the PKI-(5–24) peptide for capturing PKA catalytic subunit and the activity assay was applied for indirectly assessing the binding. Synergistic interactions of adenosine triphosphate (ATP) and the peptide inhibitor with the kinase were then investigated by a solution phase capillary electrophoretic assay, and by surface plasmon resonance technology which involved immobilization of the peptide inhibitor. After systemically evaluated by a homogeneous direct binding assay, the ATP-dependent recognition of the catalytic subunit of PKA by PKI-(5–24) was successfully transferred on to the nanomechanical cantilevers at protein concentrations of 6.6pM–66nM, exhibiting much higher sensitivity and wider dynamic range than the conventional activity assay. Thus, direct assessment of activated kinases using the cantilever sensor system functionalized with specific peptide inhibitors holds great promise in analytical applications and clinical medicine.
Keywords: Peptide inhibitor; Heat-stable protein kinase inhibitor; Cyclic adenosine monophosphate-dependent protein kinase; Nanomechanical cantilever; Surface plasmon resonance; Capillary electrophoresis; Fluorescence polarization
Development of a peptide inhibitor-based cantilever sensor assay for cyclic adenosine monophosphate-dependent protein kinase by Hyuk-Sung Kwon; Ki-Cheol Han; Kyo Seon Hwang; Jeong Hoon Lee; Tae Song Kim; Dae Sung Yoon; Eun Gyeong Yang (pp. 344-349).
A highly sensitive nanomechanical cantilever sensor assay based on an electrical measurement has been developed for detecting activated cyclic adenosine monophosphate (cyclic AMP)-dependent protein kinase (PKA). Employing a peptide derived from the heat-stable protein kinase inhibitor (PKI), a magnetic bead system was first selected as a vehicle to immobilize the PKI-(5–24) peptide for capturing PKA catalytic subunit and the activity assay was applied for indirectly assessing the binding. Synergistic interactions of adenosine triphosphate (ATP) and the peptide inhibitor with the kinase were then investigated by a solution phase capillary electrophoretic assay, and by surface plasmon resonance technology which involved immobilization of the peptide inhibitor. After systemically evaluated by a homogeneous direct binding assay, the ATP-dependent recognition of the catalytic subunit of PKA by PKI-(5–24) was successfully transferred on to the nanomechanical cantilevers at protein concentrations of 6.6pM–66nM, exhibiting much higher sensitivity and wider dynamic range than the conventional activity assay. Thus, direct assessment of activated kinases using the cantilever sensor system functionalized with specific peptide inhibitors holds great promise in analytical applications and clinical medicine.
Keywords: Peptide inhibitor; Heat-stable protein kinase inhibitor; Cyclic adenosine monophosphate-dependent protein kinase; Nanomechanical cantilever; Surface plasmon resonance; Capillary electrophoresis; Fluorescence polarization
Rapid determination of sulfonamides in milk samples using fluorescence spectroscopy and class modeling with n-way partial least squares by R. Díez; L. Sarabia; M.C. Ortiz (pp. 350-360).
In this paper, a methodology to evaluate the probability of false non-compliance and false compliance for screening methods, which give first or second-order multivariate signals is proposed. For this task 120 samples of 6 different kinds of milk have been measured by excitation–emission fluorescence. The samples have been spiked with different amounts of three sulfonamides (sulfadiazine, sulfamerazine and sulfamethazine). These substances have been classified in group B1 (veterinary medicines and contaminants) of annex I of Directive 96/23/EC. The European Union (Commission Regulation EC no. 281/96) has set the maximum residue level (MRL) of total sulfonamides at 100μgkg−1 in muscle, liver, kidney and milk.The work shows that excitation–emission fluorescence together with the partial least squares class modeling (PLS-CM) procedure may be a suitable and cheap screening method for the total amount of sulfonamides in milk. Three models, PLS-CM, have been built, for the emission and excitation spectra (first-order signals) and for the excitation–emission matrices (second-order signals). In all the cases it reaches probabilities of false compliance below 5% as required by Decision 2002/657/EC.With the same flourescence signals, the total quantity of sulfonamide was calibrated using 2-PLS, 3-PLS and PARAFAC regressions. Using this quantitative approach, the capability of detection, CCβ, around the MRL has been estimated between 114.3 and 115.1μgkg−1 for a probability of false non-compliance and false compliance equal to 5%.
Keywords: Screening method; Sulfonamides; Milk; Excitation–emission fluorescence; Decision 2002/657/EC; Capability of detection; Partial least squares class modeling; N-way partial least squares; Parallel factor analysis
Rapid determination of sulfonamides in milk samples using fluorescence spectroscopy and class modeling with n-way partial least squares by R. Díez; L. Sarabia; M.C. Ortiz (pp. 350-360).
In this paper, a methodology to evaluate the probability of false non-compliance and false compliance for screening methods, which give first or second-order multivariate signals is proposed. For this task 120 samples of 6 different kinds of milk have been measured by excitation–emission fluorescence. The samples have been spiked with different amounts of three sulfonamides (sulfadiazine, sulfamerazine and sulfamethazine). These substances have been classified in group B1 (veterinary medicines and contaminants) of annex I of Directive 96/23/EC. The European Union (Commission Regulation EC no. 281/96) has set the maximum residue level (MRL) of total sulfonamides at 100μgkg−1 in muscle, liver, kidney and milk.The work shows that excitation–emission fluorescence together with the partial least squares class modeling (PLS-CM) procedure may be a suitable and cheap screening method for the total amount of sulfonamides in milk. Three models, PLS-CM, have been built, for the emission and excitation spectra (first-order signals) and for the excitation–emission matrices (second-order signals). In all the cases it reaches probabilities of false compliance below 5% as required by Decision 2002/657/EC.With the same flourescence signals, the total quantity of sulfonamide was calibrated using 2-PLS, 3-PLS and PARAFAC regressions. Using this quantitative approach, the capability of detection, CCβ, around the MRL has been estimated between 114.3 and 115.1μgkg−1 for a probability of false non-compliance and false compliance equal to 5%.
Keywords: Screening method; Sulfonamides; Milk; Excitation–emission fluorescence; Decision 2002/657/EC; Capability of detection; Partial least squares class modeling; N-way partial least squares; Parallel factor analysis
Alternative spectrophotometric method for standardization of chlorite aqueous solutions by Marilia Philippi; Heldiane S. dos Santos; Aline O. Martins; Carla M.N. Azevedo; Marçal Pires (pp. 361-365).
The chlorite ion is the principal by-product of the treatment of drinking water by chlorine dioxide. In function of the chlorite salt instability, standard solutions of this ion need standardization by iodometric titration, which is a reliable method although labor intensive and time consuming. An alternative method to standardization of aqueous chlorite solutions, based on its direct UV absorption measurement, was presented. Besides the maximum absorption (260nm) generally used in other studies, the minimum (239nm) and isosbestic (248nm) wavelengths were proposed as supplementary points to chlorite quantification and their molar absorptivity coefficients were estimated (155.2±0.6, 104.5±1.0 and 69.0±1.2Lcm−1mol−1, respectively). The direct spectrophotometric determination of chlorite could be made selectively even in the presence of high concentration of major contaminants (chorine dioxide, chloride and chlorate), being a simple and rapid method, consuming very low volume of sample and generating low quantities of laboratory wastes.
Keywords: Chlorite; Chlorine dioxide; Interferences; Standardization; Ultra violet absorption
Alternative spectrophotometric method for standardization of chlorite aqueous solutions by Marilia Philippi; Heldiane S. dos Santos; Aline O. Martins; Carla M.N. Azevedo; Marçal Pires (pp. 361-365).
The chlorite ion is the principal by-product of the treatment of drinking water by chlorine dioxide. In function of the chlorite salt instability, standard solutions of this ion need standardization by iodometric titration, which is a reliable method although labor intensive and time consuming. An alternative method to standardization of aqueous chlorite solutions, based on its direct UV absorption measurement, was presented. Besides the maximum absorption (260nm) generally used in other studies, the minimum (239nm) and isosbestic (248nm) wavelengths were proposed as supplementary points to chlorite quantification and their molar absorptivity coefficients were estimated (155.2±0.6, 104.5±1.0 and 69.0±1.2Lcm−1mol−1, respectively). The direct spectrophotometric determination of chlorite could be made selectively even in the presence of high concentration of major contaminants (chorine dioxide, chloride and chlorate), being a simple and rapid method, consuming very low volume of sample and generating low quantities of laboratory wastes.
Keywords: Chlorite; Chlorine dioxide; Interferences; Standardization; Ultra violet absorption
Determination of trace element in Italian virgin olive oils and their characterization according to geographical origin by statistical analysis by Cinzia Benincasa; John Lewis; Enzo Perri; Giovanni Sindona; Antonio Tagarelli (pp. 366-370).
Multi-element analysis of organic virgin olive oils from different Italian regions was carried out by inductively coupled plasma mass spectrometry (ICP-MS) aiming at developing a reliable method in the traceability of the origin of oils. The data were processed by means of the chemiometric approach of linear discriminant analysis (LDA) that allows classifying unknown samples after checking possible differentiation of samples of known origin.An external calibration curve was build for the quantitative analysis. The calibration curves for each element were linear in the range between 0.01 and 100ngmL−1 and 0.2 to 2000ngmL−1, the correlation coefficients were ranging between 0.996 and 0.999. Results from spike and recovery experiments at levels of 30 and 65ngmL−1 were in the range of 91–119%, whereas the quantitation limits, based on 10 times standard deviation of the blank, were also in the range of 0.009–10.2ngg−1, for almost all the elements.
Keywords: Olive oil; Trace elements; Inductively coupled plasma mass spectrometry; Authenticity; Statistical analysis
Determination of trace element in Italian virgin olive oils and their characterization according to geographical origin by statistical analysis by Cinzia Benincasa; John Lewis; Enzo Perri; Giovanni Sindona; Antonio Tagarelli (pp. 366-370).
Multi-element analysis of organic virgin olive oils from different Italian regions was carried out by inductively coupled plasma mass spectrometry (ICP-MS) aiming at developing a reliable method in the traceability of the origin of oils. The data were processed by means of the chemiometric approach of linear discriminant analysis (LDA) that allows classifying unknown samples after checking possible differentiation of samples of known origin.An external calibration curve was build for the quantitative analysis. The calibration curves for each element were linear in the range between 0.01 and 100ngmL−1 and 0.2 to 2000ngmL−1, the correlation coefficients were ranging between 0.996 and 0.999. Results from spike and recovery experiments at levels of 30 and 65ngmL−1 were in the range of 91–119%, whereas the quantitation limits, based on 10 times standard deviation of the blank, were also in the range of 0.009–10.2ngg−1, for almost all the elements.
Keywords: Olive oil; Trace elements; Inductively coupled plasma mass spectrometry; Authenticity; Statistical analysis