Showing papers in "Analyst in 2003"
TL;DR: Spectral measurements indicated that the positions of surface plasmon resonance (SPR) bands for these nanoparticles could be tuned by varying all these parameters, and gold nanoshells with hollow interiors were shown to exhibit a much higher sensitivity to environmental changes than gold solid colloids with roughly the same size.
Abstract: This paper presents several solution-phase methods for the large-scale synthesis of metal nanoparticles with controllable compositions (e.g., spherical nanoparticles of gold/silver alloys), morphologies (e.g., nanospheres, triangular nanoplates, circular nanodisks, and nanocubes of silver), and structures (e.g., solid vs. hollow colloids). Spectral measurements indicated that the positions of surface plasmon resonance (SPR) bands for these nanoparticles could be tuned by varying all these parameters. The number of SPR peaks was found to increase as the symmetry of the nanoparticles decreased. In addition to their use as chromophores with strong extinction coefficients, these nanoparticles could serve as a platform to probe binding events of chemical and biochemical species on their surfaces. Gold nanoshells with hollow interiors were, in particular, shown to exhibit a much higher sensitivity to environmental changes than gold solid colloids with roughly the same size.
493 citations
TL;DR: Stimulated release in the caudate-putamen was pharmacologically characterized in vivo using Ro-04-1284 and pargyline, and was consistent with that expected for dopamine, and the temporal response of the sensor is slower with the more positive anodic limit.
Abstract: The voltammetric responses of carbon-fiber microelectrodes with a 1.0 V and a 1.4 V anodic limit were compared in this study. Fast-scan cyclic voltammetry was used to characterize the response to dopamine and several other neurochemicals. An increase in the adsorption properties of the carbon fiber leads to an increase in sensitivity of 9 fold in vivo. However the temporal response of the sensor is slower with the more positive anodic limit. Increased electron transfer kinetics also causes a decrease in the relative sensitivity for dopamine vs. other neurochemicals, and a change in their cyclic voltammograms. Stimulated release in the caudate-putamen was pharmacologically characterized in vivo using Ro-04-1284 and pargyline, and was consistent with that expected for dopamine.
360 citations
TL;DR: The preparation and attractive performance of carbon-nanotube modified glassy-carbon (CNT/GC) electrodes for improved detection of purines, nucleic acids, and DNA hybridization are described and factors influencing the enhancement of the guanine signal are assessed and optimized.
Abstract: The preparation and attractive performance of carbon-nanotube modified glassy-carbon (CNT/GC) electrodes for improved detection of purines, nucleic acids, and DNA hybridization are described. The surface-confined multiwall carbon-nanotube (MWCNT) facilitates the adsorptive accumulation of the guanine nucleobase and greatly enhances its oxidation signal. The advantages of CNT/GC electrodes are illustrated from comparison to the common unmodified glassy carbon, carbon paste and graphite pencil electrodes. The dramatic amplification of the guanine signal has been combined with a label-free electrical detection of DNA hybridization. Factors influencing the enhancement of the guanine signal are assessed and optimized. The performance characteristics of the amplified label-free electrochemical detection of DNA hybridization are reported in connection to measurements of nucleic-acid segments related to the breast-cancer BRCA1 gene.
278 citations
TL;DR: In this article, the field of mercury film electrodes (MFE's) as electroanalytical devices is reviewed, with special emphasis placed on the area of new materials as substrates for the mercury coating and the mercury plating process.
Abstract: In this article, the field of mercury film electrodes (MFE's) as electroanalytical devices is reviewed. Special emphasis is placed on the area of new materials as substrates for the mercury coating and the mercury plating process as well as on the developments related to the electrode modification used to achieve an increase in either the selectivity and/or the sensitivity of the analysis. Other topics discussed are microelectrodes, disposable electrodes and some novel, innovative or less well explored applications of electroanalytical methods using MFE's. The future prospects, potential uses and alternatives for MFE's in electroanalysis are finally discussed.
219 citations
TL;DR: The benefits of stimulus-sensitive hydrogels, their miniaturisation and the use of 365 nm UV-photolithography as a fast economical manufacturing technique are discussed.
Abstract: In this tutorial review the use of stimulus-sensitive hydrogels as sensors and actuators for (micro)analytical applications is discussed. The first part of the article is aimed at making the reader familiar with stimulus-sensitive hydrogels, their chemical composition and their chemo-physical behavior. The prior art in the field, that comprises a number of sensors ranging from metal ion-sensitive sensors to antigen-sensitive sensors and a few actuators, is also treated in this part. The second part of the article focusses on the use of stimulus-sensitive hydrogels for microsensors and microactuators as well as their application in micro total analysis systems. The benefits of stimulus-sensitive hydrogels, their miniaturisation and the use of 365 nm UV-photolithography as a fast economical manufacturing technique are discussed.
210 citations
TL;DR: The preliminary results showed that there was a relationship between serum metabolic profiles and blood pressure which, in part, was due to lipoprotein particle composition differences between the samples, and indicated that serum pathology associated with blood pressure is apparent at SBP values > 130 mm Hg, which the WHO and ISH currently define as the limit between normal and high-normal.
Abstract: The application of chemometric methods to 1H NMR spectroscopic data has been documented for pathophysiological processes. In this study we show the application of 1H NMR-based metabonomics to investigate a relationship between serum metabolic profiles and hypertension. Although hypertension can be defined using blood pressure measurements, the underlying aetiology and metabolic effects are not so readily identified. Serum profiles for patients with low/normal systolic blood pressure (SBP ≤ 130 mm Hg; n = 28), borderline SBP (131–149 mm Hg; n = 19) and high SBP (≥ 150 mm Hg; n = 17) were acquired using 1H NMR spectroscopy. Orthogonal signal correction followed by principal components analysis were applied to these NMR data in order to facilitate interpretation, and the resulting chemometric models were validated using Soft Independent Modelling of Class Analogy. Using 1H NMR-based metabonomics, it was possible to distinguish low/normal SBP serum samples from borderline and high SBP samples. Borderline and high SBP samples, however, were indiscriminate from each other. Our preliminary results showed that there was a relationship between serum metabolic profiles and blood pressure which, in part, was due to lipoprotein particle composition differences between the samples. Furthermore, our results indicated that serum pathology associated with blood pressure is apparent at SBP values > 130 mm Hg, which the WHO and ISH currently define as the limit between normal and high-normal.
185 citations
TL;DR: The anodic stripping voltammetry at a carbon paste electrode modified with thiol terminated self-assembled monolayer on mesoporous silica (SH-SAMMS) provides a new sensor for simultaneous detection of lead (Pb2+) and mercury (Hg2+) in aqueous solutions.
Abstract: The anodic stripping voltammetry at a carbon paste electrode modified with thiol terminated self-assembled monolayer on mesoporous silica (SH-SAMMS) provides a new sensor for simultaneous detection of lead (Pb2+) and mercury (Hg2+) in aqueous solutions. The overall analysis involved a two-step procedure: an accumulation step at open circuit, followed by medium exchange to a pure electrolyte solution for the stripping analysis. Factors affecting the performance of the SH-SAMMS modified electrodes were investigated, including electrode activation and regeneration, electrode composition, preconcentration time, electrolysis time, and composition of electrolysis and stripping media. The most sensitive and reliable electrode contained 20% SH-SAMMS and 80% carbon paste. The optimal operating conditions were a sequence with a 2 min preconcentration period, then a 60 s electrolysis period of the preconcentrated species in 0.2 M nitric acid, followed by square wave anodic stripping voltammetry from −1.0 V to 0.6 V in 0.2 M nitric acid. The areas of the peak responses were linear with respect to metal ion concentrations in the ranges of 10–1500 ppb Pb2+ and 20–1600 ppb Hg2+. The detection limits for Pb2+ and Hg2+ were 0.5 ppb Pb2+ and 3 ppb Hg2+ after a 20 min preconcentration period.
166 citations
TL;DR: The potential use of a class-specific enzyme-linked immunosorbent assay (ELISA) in studying the occurrence and fate of tetracyclines in the environment was evaluated and it was found that ELISA provides an alternative method for conducting environmental fate and transport studies of antibiotics.
Abstract: The potential use of a class-specific enzyme-linked immunosorbent assay (ELISA) in studying the occurrence and fate of tetracyclines in the environment was evaluated. Several manure samples collected from hog lagoons and cattle feedlots were screened for the presence of tetracycline residues using ELISA. The levels varied from less than the detection limit (0.5 parts per billion) to 200 parts per million. The degradation of tetracyclines in soil-applied manure was followed using ELISA to measure the decline in tetracycline concentrations. Low levels of tetracyclines remained detectable in soil for up to 28 days. The ELISA procedure also proved useful in determining the leaching potential of tetracyclines in undisturbed soil columns and in the analysis of total tetracyclines in manure, soil, and water. Based on the cross-reactivity of the antibodies employed, this ELISA method can be an important screening tool for the presence of other tetracycline compounds, such as chlortetracycline and oxytetracycline. The ELISA method also detects the epimers of tetracyclines and the corresponding dehydration by-products, anhydrotetracyclines. Analysis of selected manure extracts by liquid chromatography with mass spectrometry (LC-MS) showed lower concentrations of total tetracyclines compared to the values obtained by ELISA, indicating the presence of other structurally related compounds or transformation products of tetracyclines being detected by ELISA in the samples. Because analysis of manure and soil samples by LC-MS requires extensive clean-up procedures, ELISA provides an alternative method for conducting environmental fate and transport studies of antibiotics.
144 citations
TL;DR: Preliminary results suggest that HPLC-MS-based approaches may have a useful role in metabonomic analysis that complements existing approaches.
Abstract: The application of HPLC-MS combined with principal components analysis (PCA) to the metabonomic analysis of mouse urine is demonstrated. Urine samples from three strains of mouse were analysed by gradient HPLC-MS combined with positive and negative electrospray time-of-flight mass spectrometry. Analysis of the resulting data using PCA enabled the samples to be discriminated between on the basis of gender, strain and diurnal variation. These preliminary results suggest that HPLC-MS-based approaches may have a useful role in metabonomic analysis that complements existing approaches.
140 citations
TL;DR: In this paper, Fe3O4 nanoparticles cast on pyrolytic graphite (PG) electrodes were used to immobilize hemoglobin (Hb), myoglobin (Mb), and horseradish peroxidase (HRP).
Abstract: Fe3O4 nanoparticles cast on pyrolytic graphite (PG) electrodes were used to immobilize hemoglobin (Hb), myoglobin (Mb) and horseradish peroxidase (HRP). The Fe3O4 nanoparticles provided a favorable microenvironment for the proteins to directly transfer electrons with electrodes. The protein–Fe3O4 films were used to electrochemically catalyze the reduction of oxygen, trichloroacetic acid, nitrite and hydrogen peroxide, and showed a potential applicability in fabricating biosensors. Transmission electron microscopy (TEM), UV–visible absorption and reflectance absorption infrared (RAIR) spectroscopy, and cyclic and square wave voltammetry, were used to characterize the films.
139 citations
TL;DR: In the absence of a precisely characterized Hg isotope ratio standard, the authors were not able to determine unambiguously the absolute Hg ratios of the ore samples, highlighting the urgent need for certified standard materials.
Abstract: Variations in Hg isotope ratios in cinnabar ores obtained from different countries were detected by high precision isotope ratio measurements using multi-collector inductively coupled mass spectrometry (MC-ICP-MS). Values of δ198/202Hg varied from 0.0–1.3‰ relative to a NIST SRM 1641d Hg solution. The typical external uncertainty of the δ values was 0.06 to 0.26‰. Hg was introduced into the plasma as elemental Hg after reduction by sodium borohydride. A significant fractionation of lead isotopes was observed during the simultaneous generation of lead hydride, preventing normalization of the Hg isotope ratios using the measured 208/206Pb ratio. Hg ratios were instead corrected employing the simultaneously measured 205/203Tl ratio. Using a 10 ng ml−1 Hg solution and 10 min of sampling, introducing 60 ng of Hg, the internal precision of the isotope ratio measurements was as low as 14 ppm. Absolute Hg ratios deviated from the representative IUPAC values by approximately 0.2% per u. This observation is explained by the inadequacy of the exponential law to correct for mass bias in MC-ICP-MS measurements. In the absence of a precisely characterized Hg isotope ratio standard, we were not able to determine unambiguously the absolute Hg ratios of the ore samples, highlighting the urgent need for certified standard materials.
TL;DR: The modification of electrodes with the tripeptide Gly-Gly-His for the detection of copper in water samples exhibited high sensitivity to copper which is attributed to the stable 4N coordinate complex the peptide formed around the metal ion to give copper the preferred tetragonal coordination.
Abstract: The modification of electrodes with the tripeptide Gly–Gly–His for the detection of copper in water samples is described in detail. The tripeptide modified electrode was prepared by first self-assembling 3-mercaptopropionic acid (MPA) onto the gold electrode followed by covalent attachment of the tripeptide to the self-assembled monolayer using carbodiimide coupling. The electrodes were characterized using electrochemistry, a newly developed mass-spectrometry method and quantum mechanical calculations. The mass spectrometry confirmed the modification to proceed as expected with peptide bonds formed between the carboxylic acids of the MPA and the terminal amine of the peptide. Electrochemical measurements indicated that approximately half the MPA molecules in a SAM are modified with the peptide. The peptide modified electrodes exhibited high sensitivity to copper which is attributed to the stable 4N coordinate complex the peptide formed around the metal ion to give copper the preferred tetragonal coordination. The formation of a 4 coordinate complex was predicted using quantum mechanical calculation and confirmed using mass spectrometry. The adsorption of the copper to the peptide modified electrode was consistent with a Langmuir isotherm with a binding constant of (8.1 ± 0.4) 1010 M−1 at 25 °C.
TL;DR: This Highlight article discusses the recent developments in nanosensor technology and investigates the use of more complex sensing schemes that will expand the range of analytes that can be detected and quantified.
Abstract: Optical nanosensors have been designed to utilise the sensitivity of fluorescence for making quantitative measurements in the intracellular environment, using devices that are small enough to be inserted into living cells with a minimum of physical perturbation. Advantages over widely used fluorescence dye based methods are observed because the nanosensor matrix imparts two key benefits; (1) protection of the sensing component from interfering species within the intracellular environment and (2) protection of the intracellular environment from any toxic effects of the sensing component. This Highlight article discusses the recent developments in nanosensor technology and investigates the use of more complex sensing schemes that will expand the range of analytes that can be detected and quantified.
TL;DR: It can be concluded that a method based on NIR spectroscopy and multivariate calibration can be employed for the determination of sulfur in diesel fuels and the selection of variables can provide more robust calibration models and SPA provided more parsimonious models than GA.
Abstract: A method for sulfur determination in diesel fuel employing near infrared spectroscopy, variable selection and multivariate calibration is described. The performances of principal component regression (PCR) and partial least square (PLS) chemometric methods were compared with those shown by multiple linear regression (MLR), performed after variable selection based on the genetic algorithm (GA) or the successive projection algorithm (SPA). Ninety seven diesel samples were divided into three sets (41 for calibration, 30 for internal validation and 26 for external validation), each of them covering the full range of sulfur concentrations (from 0.07 to 0.33% w/w). Transflectance measurements were performed from 850 to 1800 nm. Although principal component analysis identified the presence of three groups, PLS, PCR and MLR provided models whose predicting capabilities were independent of the diesel type. Calibration with PLS and PCR employing all the 454 wavelengths provided root mean square errors of prediction (RMSEP) of 0.036% and 0.043% for the validation set, respectively. The use of GA and SPA for variable selection provided calibration models based on 19 and 9 wavelengths, with a RMSEP of 0.031% (PLS-GA), 0.022% (MLR-SPA) and 0.034% (MLR-GA). As the ASTM 4294 method allows a reproducibility of 0.05%, it can be concluded that a method based on NIR spectroscopy and multivariate calibration can be employed for the determination of sulfur in diesel fuels. Furthermore, the selection of variables can provide more robust calibration models and SPA provided more parsimonious models than GA.
TL;DR: The suppression of the internal standard by increasing concentrations of the co-eluting analyte in calibration series and plasma samples analysed by LC-ESI-MS was studied using the isotope dilution technique.
Abstract: The suppression of the internal standard by increasing concentrations of the co-eluting analyte in calibration series and plasma samples analysed by LC-ESI-MS was studied using the isotope dilution technique. A series of three analyte/deuterated analyte pairs including fexofenadine/d6-fexofenadine, dapsone/d4-dapsone and peudoephedrine/d3-ephedrine were investigated. Suppression of the internal standard signal was noticed in extracted plasma samples containing fexofenadine and d6-fexofenadine as internal standard, as well as in solvent based calibration solutions of the three pair of compounds noted above during LC-ESI-MS analysis at flow rates greater than 100 μL min−1. This signal suppression effect was described by invoking Enke’s model of electrospray ion generation. This model suggests that signal suppression can be ascribed to the competition between ionic species for charged surface sites present on the generated droplets during the electrospray process. The slopes of the calibration curves of the three analytes were close to unity (fexofenadien/d6-fexofenadine 0.964 ± 0.008, pseudoephedrine/d3-ephedrine 1.02 ± 0.080 and dapsone/d4-dapsone 0.905 ± 0.048) as predicted by the model, indicating that quantitation should not be affected by the variation in the peak area of the internal standard.
TL;DR: The Langmuir-Freundlich isotherm is used to model the interaction of several triazines with a propazine-imprinted polymer and to explain the observed cross-reactivity, suggesting that the use of this new methodology can open new pathways for understanding how molecular recognition in imprinted polymers takes place.
Abstract: In this paper, the Langmuir-Freundlich isotherm is used to model the interaction of several triazines (desethylatrazine, desisopropylatrazine, simazine, atrazine, propazine and prometryn) with a propazine-imprinted polymer and to explain the observed cross-reactivity. Different rebinding experiments (each herbicide alone or all together in a mixture) were carried out and the experimental binding isotherms were fitted to the Langmuir-Freundlich isotherm. The fitting coefficients obtained (total number of binding sites, mean binding affinity and heterogeneity index) allowed the description of the kind of binding sites present in the imprinted polymer under study. It was concluded that the recognition mechanism was mainly governed by the molecular size although slight differences in the molecular structure may also play an important role. The obtained results suggest that the use of this new methodology can open new pathways for understanding how molecular recognition in imprinted polymers takes place.
TL;DR: The attractive performance of the new needle electrode offers great promise for continuous monitoring of glucose in connection to the management of diabetes, and for the biosensing of other metabolites.
Abstract: The preparation of an enzyme-dispersed carbon-nanotube (CNT) electrode, based on mixing glucose oxidase (GOx) within CNT, is described. The new binderless biocomposite was packed within a 21-gauge needle and used for amperometric monitoring of glucose. The resulting microsensor offers a low-potential highly selective and sensitive detection of glucose. The high sensitivity and selectivity are coupled to a wide linear range, prolonged lifetime and oxygen independence. About 80% of the GOx activity is retained during a 24 h thermal stress at 90 °C, reflecting the enzyme-stabilization action of CNT. The marked electrocatalytic action towards hydrogen peroxide allows highly selective detection of the glucose substrate at −0.1 V (vs. Ag/AgCl) with no interferences from coexisting ascorbic acid, acetaminophen or uric acid. Linearity prevails up to 40 mM glucose (with analytically useful signals observed up to 0.1 M). Factors affecting the performance of the CNT-based glucose biosensor were assessed and optimized. The attractive performance of the new needle electrode offers great promise for continuous monitoring of glucose in connection to the management of diabetes, and for the biosensing of other metabolites.
TL;DR: This review focuses on applications of cavity ring-down spectroscopy that will be of interest to environmental chemists and analytical chemists working on environmental problems.
Abstract: Cavity ring-down (CRD) is a sensitive variant of traditional absorption spectroscopy that has found increasing use in a number of chemical measurement applications This review focuses on applications of cavity ring-down spectroscopy that will be of interest to environmental chemists and analytical chemists working on environmental problems The applications are classified into direct monitoring approaches, indirect analysis methods and ancillary studies and a differentiation is made between field-tested instruments and proof of principle studies
TL;DR: The obtained RAM-MIP forPRP showed excellent molecular recognition ability for PRP, good ones for alprenolol (ALP) and pindolol, and fair ones for other beta-blockers, and could be applicable for the assay of ALP enantiomers at the therapeutic plasma levels.
Abstract: A restricted access media-molecularly imprinted polymer (RAM-MIP) for propranolol (PRP) has been prepared for direct injection analysis of β-blockers in biological fluids. First, the MIP for PRP was prepared using methacrylic acid and ethylene glycol dimethacrylate as the functional monomer and cross-linker, respectively, by a multi-step swelling and polymerization method. Next, a 1:1 mixture of glycerol monomethacrylate and glycerol dimethacrylate was used for hydrophilic surface modification, and added directly to the MIP for PRP after 4 h from the start of polymerization. Then further polymerization was carried out for 20 h. The obtained RAM-MIP for PRP showed excellent molecular recognition ability for PRP, good ones for alprenolol (ALP) and pindolol, and fair ones for other β-blockers. The RAM-MIP was applied for direct injection analysis of ALP enantiomers in a rat plasma sample by a column-switching HPLC system using a β-cyclodextrin phenylcarbamate-bonded silica column as the analytical column. The calibration graph, constructed from peak area versus each ALP enantiomer concentration, was linear with a correlation coefficient of >0.999 over the concentration ranges of 12.5–250 ng ml−1. The limit of quantitation was 12.5 ng ml−1 with a 50 μl injection. This method could be applicable for the assay of ALP enantiomers at the therapeutic plasma levels, and have wide applicability for the assay of β-blockers in biological fluids.
TL;DR: A pulsed corona discharge ionisation source, a candidate replacement for 63Ni ionisation sources for ion mobility spectrometry, is described along with a new design of ion mobilitySpectrometer-mass spectrometer to enable the mobility spectra, atmospheric chemical ionisation mass spectra and selected-mass Mobility spectra to be obtained.
Abstract: A pulsed corona discharge ionisation source, a candidate replacement for 63Ni ionisation sources for ion mobility spectrometry, is described along with a new design of ion mobility spectrometer-mass spectrometer. Preliminary research on the characterisation of the reactant ion peaks associated with the use of this ionisation source was undertaken by assembling a pulsed corona discharge ionisation switchable high-resolution ion mobility spectrometer-mass spectrometer to enable the mobility spectra, atmospheric chemical ionisation mass spectra and selected-mass mobility spectra to be obtained. With ammonia doping at 2.39 mg m−3 in air and a water content of approximately 80 mg m−3 in the positive mode the observed response was attributable to the formation of [(H2O)nNH4]+ and [(H2O)n(NH3)NH4]+ in the reaction region. The observed responses in the negative mode were more complex with evidence for the formation [(H2O)nO2]−, [(H2O)nCO3]−, [(H2O)nHCO3]−, [(H2O)nCO4]− and [(H2O)nNO3]−. The responses due to these species were clearly discernible in the resultant mobility spectra, with enough oxygen-based species formed to support analytically useful responses.
TL;DR: The results of the analysis of the biomarkers in the urine of 44 volunteers were used to develop a predictive model for smoking status, using discriminant analysis, and the classification model correctly classified 93.2% of cross-validated grouped cases.
Abstract: A method using gas chromatography (GC)-mass spectrometry (MS) for the simultaneous determination of the smoke uptake parameters thiocyanate, nicotine and cotinine in human tissues is reported. Nicotine, cotinine and thiocyanate, in combination with a phase-transfer catalyst, were extracted from urine, saliva and hair into dichloromethane (DCM). Thiocyanate was alkylated in the DCM-layer to form a pentafluorobenzyl derivative. The biochemical markers in DCM were directly injected into the GC system and separated on a DB-1MS column using a 9.4 min temperature program. The method was validated in urine and saliva between the limits of quantitation (1.0–15 µg ml−1 thiocyanate, 0.010–3.0 µg ml−1 nicotine and cotinine in urine, 0.010–1.0 µg ml−1 nicotine and cotinine in saliva). The calibration curves were found to be linear (r > 0.996), the within- and between-day accuracy's were 83–120%, the repeatability coefficients of variation were 3–20% and the limits of detection were 0.060 ng ml−1 thiocyanate and 0.60 ng ml−1 nicotine and cotinine. The results of the analysis of the biomarkers in the urine of 44 volunteers were used to develop a predictive model for smoking status, using discriminant analysis. The classification model correctly classified 93.2% of cross-validated grouped cases. Saliva samples were used to confirm the results of the classification method.
TL;DR: In this article, the detection of ionic species in a polymeric planar electrophoresis device by contactless conductivity measurement is described, which allows the use of bare devices as used for optical measurements, which greatly simplifies the method.
Abstract: The detection of ionic species in a polymeric planar electrophoresis device by contactless conductivity measurement is described. To our knowledge this is the first report of such measurements carried out with external electrodes which are part of the holder rather than the separation chip itself. The approach allows the use of bare devices as used for optical measurements, which greatly simplifies the method. The use of a sine wave of 100 kHz of a high amplitude of 500 V for cell excitation assures high sensitivity which is demonstrated with electropherograms for alkali and heavy metal ions as well as inorganic anions and carboxylates at concentrations between 10 and 50 µM. The determination of underivatized amino acids was also possible by using a buffer in the alkaline region where these species are present in anionic form. Detection limits were found to be in the order of 1–5 µM for the inorganic ions and between about 5 and 50 µM for the organic species.
TL;DR: Comparison of the square root of the sum frequency intensity to that of the Raman multiplied by the infrared intensity provides additional information about the molecular environment at their respective air-liquid interface.
Abstract: The air–liquid interface and the liquid-phase of benzene, toluene, 1,3-dimethylbenzene, and 1,3,5-trimethylbenzene are studied using broad bandwidth sum frequency generation spectroscopy, Raman and infrared spectroscopy A vibrationally resonant sum frequency response is observed from these surfaces in spite of the small hyperpolarizabilities, in particular, the zero and near-zero hyperpolarizabilities of benzene and 1,3,5-trimethylbenzene The orientation of the aromatic rings of these compounds at their air–liquid interfaces is tilted relative to the surface plane Thus, on average, the plane of the aromatic ring does not lie in the interfacial plane Comparison of the square root of the sum frequency intensity to that of the Raman multiplied by the infrared intensity provides additional information about the molecular environment at their respective air–liquid interface
TL;DR: The multi-walled carbon nanotubes (MWCNTs) were successfully immobilized on the surface of a glassy carbon electrode by mixing with horse-radish peroxidase (HRP) to create the MWCNTs-HRP modified electrode, which showed excellent response of reduction current for the determination of H2O2 at the potential of -300 mV.
Abstract: In this paper, multi-walled carbon nanotubes (MWCNTs) were successfully immobilized on the surface of a glassy carbon electrode by mixing with horse-radish peroxidase (HRP). The electrochemical behavior of H2O2 was also studied with the MWCNTs–HRP modified electrode as a working electrode. The MWCNTs–HRP modified electrode showed excellent response of reduction current for the determination of H2O2 at the potential of −300 mV (vs. Ag/AgCl). We assembled the MWCNTs–HRP modified electrode in a thin-layer flow cell and the H2O2 solution was continuously introduced into the cell with a syringe pump. We optimized the sensitivity of the H2O2 sensor by adjusting the working potential and the pH of the buffer solution. The peak current increased linearly with the concentration of H2O2 in the range 3.0 × 10−7
∼ 2.0 × 10−4 mol L−1. The detection limit is 1.0 × 10−7 mol L−1 (S/N = 3). The interferences from ascorbic acid, uric acid and other electroactive substances can be greatly excluded since the sensor can be operated at −300 mV. Stability and reproducibility of the MWCNTs–HRP chemically modified electrode were also studied in this paper. Fabricated with glucose and lactate oxidase, the MWCNTs–HRP electrode was also applied to prepare the on-line glucose and lactate biosensors because of the high sensitivity for the determination of H2O2.
TL;DR: In this article, the binding energy between monomer and template was calculated by a semi-empirical quantum method and ab initio method with 6-31G basis set, and the chromatographic characteristics of the template on a MIP column was investigated.
Abstract: In order to study the nature of recognition of a molecular imprinting polymer (MIP) and improve its performance, we used a computational approach to evaluate the MIP system. We mainly focused on the monomer–template interaction in prepolymerization. Firstly, the possible minimum energy conformation of the monomer and template was opimized by Gaussian 94 quantum software. Then the binding energy between monomer and template was calculated by a semi-empirical quantum method and ab initio method with 6-31G basis set. Finally, the chromatographic characteristics of the template on a MIP column was investigated. In either a PAM or p-BA system, a correlation was found to exist between the binding energy and the capacity factor (k′) in our experimental conditions. The higher the binding energy was, the larger the capacity factor was. This demonstrated that the higher binding energy between monomer and template was likely to lead to a more stable complex in prepolymerization. Therefore, more high affinity binding sites in the polymer were left and subsequently the capacity factor was larger. Additionally, we have also studied the influence of intramolecular hydrogen bonds in the PAM system and polyclonity of MIP by computer simulation. We think the computer simulation method proposed by us in this paper is a new and fast evaluation method which may be applied into studying MIP's properties.
TL;DR: These newly developed NFHS particles have been used as a fluorescent marker to label antibodies, using silica immobilization method, for the immunoassay of human alpha-fetoprotein (AFP).
Abstract: Nanometer-sized fluorescent hybrid silica (NFHS) particles were prepared for use as sensitive and photostable fluorescent probes in biological staining and diagnostics. The first step of the synthesis involves the covalent modification of 3-aminopropyltrimethoxysilane with an organic fluorophore, such as fluorescein isothiocyanate, under N2 atmosphere for getting a fluorescent silica precursor. Then the NFHS particles, with a diameter of well below 40 nm, were prepared by controlled hydrolysis of the fluorescent silica precursor with tetramethoxysilane (TMOS) using the reverse micelle technique. The fluorophores are dispersed homogeneously in the silica network of the NFHS particles and well protected from the environmental oxygen. Furthermore, since the fluorophores are covalently bound to the silica network, there is no migration, aggregation and leakage of the fluorophores. In comparison with common single organic fluorophores, these particle probes are brighter, more stable against photobleaching and do not suffer from intermittent on/off light emission (blinking). We have used these newly developed NFHS particles as a fluorescent marker to label antibodies, using silica immobilization method, for the immunoassay of human alpha-fetoprotein (AFP). The detection limit of this method was down to 0.05 ng mL(-1) under our current experimental conditions. We think this material would attract much attention and be applied widely in biotechnology.
TL;DR: The analysis of Pelargonium graveolens essential oil was reported using comprehensive two-dimensional gas chromatography with quadrupole mass spectrometric detection (GC×GC-qMS) as mentioned in this paper.
Abstract: The analysis of Pelargonium graveolens essential oil is reported using comprehensive two-dimensional gas chromatography with quadrupole mass spectrometric detection (GC×GC-qMS). A spectral acquisition rate of 20 Hz was achieved by using a reduced mass scan range of 188 u. 65 components were identified within the two-dimensional separation space based upon retention index and mass spectral matching with literature data. Very high quality mass spectra were obtained, which facilitated accurate library matching, without the need for background correction. High efficiency in the short, fast-GC second dimension column was achieved by applying the principles of vacuum-GC. It is demonstrated that facile determination of the key citronellol : geraniol ratio and the amount of 10-epi-γ-eudesmol in geranium essential oils using GC×GC will be possible. The method should be generally suited to the analysis of similar essential oil samples.
TL;DR: In this paper, stable silver coated gold hydrosols, with particle size varying from 12-200 nm, were prepared and tested as a substrate for surface enhanced Raman scattering (SERS).
Abstract: Stable silver coated gold hydrosols, with particle size varying from 12–200 nm, were prepared and tested as a substrate for surface enhanced Raman scattering (SERS). Nanoparticles containing a 12 nm gold core and coated with a silver shell varying from 0–100 nm were prepared. It is shown that SERS sensitivity depends on the Ag shell thickness and nanoparticle size. The optimum particle size for SERS was found to be between 25–50 nm. These particles can detect 5 × 10−11 mol dm−3 4-mercaptopyridine and 5 × 10−10 mol dm−3 rhodamine 6G.
TL;DR: The authors' experiments indicated that the IL-coated capillary could work stably in the run buffer for at least 96 h with no notable deterioration in performance.
Abstract: An ionic liquid (IL) coated capillary was prepared and investigated for DNA separation. The electroosmotic flow of the capillary was reversed between pH 4.5 and 9. Below 900 base pairs the larger DNA fragment suffered more retardation in the IL coated capillary due to the increasing charge density of the fragment with size. In the presence of 4% hydroxyethylcellulose, the ΦX174 DNA-Hae III digest fragments were baseline separated in both IL- and polyacrylamide-coated capillary except for the fragments of 271 and 281 base pairs; while the analysis time was shorter in the IL-coated capillary. Our experiments indicated that the IL-coated capillary could work stably in the run buffer for at least 96 h with no notable deterioration in performance.