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Analytica Chimica Acta (v.643, #1-2)
Potential of high temperature liquid chromatography for the improvement of separation efficiency—A review by Thorsten Teutenberg (pp. 1-12).
This review has been written in the context of critically evaluating the potential of high temperature liquid chromatography for the improvement of separation efficiency. The focus of this review is also laid on a critical evaluation of the applicability of this technique in a regulated environment. The review tries to give an overview over all aspects which can lead to a deterioration of the separation efficiency. This means that the discussion is not limited to a theoretical treatment of the van Deemter equation, but that all aspects which can contribute to a loss of efficiency are covered. This includes the design of the heating equipment as well as the possible degradation of the stationary phase or analytes. Therefore, the review is also a general review which tries to include the latest findings on high temperature HPLC. Also, temperature programming is critically evaluated. It is outlined that this technique is a prerequisite for certain hyphenation techniques like isotope ratio mass spectrometry or flame ionisation detection. However, it is critically discussed if temperature programming also will improve the separation efficiency.
Keywords: High temperature liquid chromatography; Superheated water chromatography; Separation efficiency; van’t Hoff plot; Selectivity; Mobile phase preheating; Temperature programming; Heating systems; Column degradation; Analyte stability; Isotope ratio mass spectrometry; Hyphenation techniques
A novel biosensor based on photoelectro-synergistic catalysis for flow-injection analysis system/amperometric detection of organophosphorous pesticides by Yinyin Wei; Ying Li; Yunhe Qu; Fei Xiao; Guoyue Shi; Litong Jin (pp. 13-18).
In this study, a highly sensitive amperometric biosensor based on photoelectro-synergistic catalysis for detecting organophosphorus pesticides (OPs) in flow-injection analysis (FIA) system has been developed. The acetylcholinesterase enzyme (AChE) was immobilized by adsorption into the nanostructured PbO2/TiO2/Ti, which also acted as the working electrode. This strategy was found to catalyze the oxidative reaction of thiocholine effectively, make the AChE/PbO2/TiO2/Ti biosensor detect the substrate at 0.30V (vs. SCE), hundreds milli-volts lower than others reported. PbO2/TiO2/Ti and TiO2/Ti electrodes were prepared and investigated with atomic force microscope (AFM). Factors influencing the performance were optimized. The resulting flow system offered a fast, sensitive, and stable response. A value of 1.34mM for the apparent Michaelis–Menten constant(KMapp) was obtained. A wide linear inhibition response for trichlorfon was observed in the range of 0.01–20μM with the detection limit of 0.1nM. The results using this biosensor agreed very well with chromatographic method and we also examined the real samples successfully in this work.
Keywords: Biosensor; Photoelectro-synergistic catalysis; Acetylcholinesterase; Organophosphorus pesticides
Trace vanadium analysis by catalytic adsorptive stripping voltammetry using mercury-coated micro-wire and polystyrene-coated bismuth film electrodes by Royce Dansby-Sparks; James Q. Chambers; Zi-Ling Xue (pp. 19-25).
An electrochemical technique has been developed for ultra-trace (ngL−1) vanadium (V) measurement. Catalytic adsorptive stripping voltammetry for V analysis was developed at mercury-coated gold micro-wire electrodes (MWEs, 100μm) in the presence of gallic acid (GA) and bromate ion. A potential of −0.275V (vs Ag/AgCl) was used to accumulate the complex in acetate buffer (pH 5.0) at the electrode surface followed by a differential pulse voltammetric scan. Parameters affecting the electrochemical response, including pH, concentration of GA and bromate, deposition potential and time have been optimized. Linear response was obtained in the 0–1000ngL−1 range (2min deposition), with a detection limit of 0.88ngL−1. The method was validated by comparison of results for an unknown solution of V by atomic absorption measurement. The protocol was evaluated in a real sample by measuring the amount of V in river water samples. Thick bismuth film electrodes with protective polystyrene films have also been made and evaluated as a mercury free alternative. However, ngL−1 level detection was only attainable with extended (10min) deposition times. The proposed use of MWEs for the detection of V is sensitive enough for future use to test V concentration in biological fluids treated by the advanced oxidation process (AOP).
Keywords: Vanadium; Gallic acid; Catalytic adsorptive stripping voltammetry; Micro-wire electrode
Immobilization, hybridization, and oxidation of synthetic DNA on gold surface: Electron transfer investigated by electrochemistry and scanning tunneling microscopy by Gerald D. McEwen; Fan Chen; Anhong Zhou (pp. 26-37).
Fundamental understanding of interfacial electron transfer (ET) among electrolyte/DNA/solid-surface will facilitate the design for electrical detection of DNA molecules. In this report, the electron transfer characteristics of synthetic DNA (sequence from pathogenic Cryptosporidium parvum) self-assembled on a gold surface was electrochemically studied. The effects of immobilization order on the interface ET related parameters such as diffusion coefficient ( D0), surface coverage ( θR), and monolayer thickness ( di) were determined by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). DNA surface density ( ΓDNA) was determined by the integration of the charge of the electro-oxidation current peaks during the initial cyclic voltammetry scans. It was found that the DNA surface densities at different modifications followed the order: ΓDNA (dsS-DNA/Au)> ΓDNA (MCH/dsS-DNA/Au)> ΓDNA (dsS-DNA/MCH/Au). It was also revealed that the electro-oxidation of the DNA modified gold surface would involve the oxidation of nucleotides (guanine and adenine) with a 5.51 electron transfer mechanism and the oxidative desorption of DNA and MCH molecules by a 3 electron transfer mechanism. STM topography and current image analysis indicated that the surface conductivity after each surface modification followed the order: dsS-DNA/Au
Keywords: DNA immobilization; Scanning tunneling microscopy; Gold electrode; Hoechst 33258; Electron transfer; DNA oxidative damage
Fabrication of a molecularly imprinted polymer sensor by self-assembling monolayer/mediator system by Po-Yen Chen; Po-Chin Nien; Cheng-Tar Wu; Tsing-Hua Wu; Chii-Wann Lin; Kuo-Chuan Ho (pp. 38-44).
Detection of dopamine (DA) by using a molecularly imprinted polymer (MIP) which fabricated by the self-assembling monolayer (SAM)/mediator system was studied. The SAM was made by attaching thioglycolic acid (TGA) on a gold electrode and quercetin (Q) was selected as an electron transfer mediator in this system. Methyl methacrylate (MMA) was polymerized by photopolymerization with the addition of dopamine to form a MIP electrode. The MIP and non-MIP (NMIP) modified electrodes were identified by FTIR and scanning electrochemical microscopy (SECM) approach curves. DA was detected by an amperometric method at a constant potential of 0.45V and obtained a sensitivity of 0.445mAcm−2M−1. The imprinting efficiency approaches infinity due to a non-reactive surface of NMIP. In the interference test, ascorbic acid contributed less than 12% of current response in the coexistence solution with DA and the performance is highly related to the concentration of template added during the fabrication process.
Keywords: Artificial enzyme; Imprinting efficiency; Molecularly imprinted polymer; Scanning electrochemical microscopy; Self-assembly monolayer
Electrochemical investigations of the interaction of C-reactive protein (CRP) with a CRP antibody chemically immobilized on a gold surface by Hooman Hennessey; Nadia Afara; Sasha Omanovic; Ante L. Padjen (pp. 45-53).
A possibility of using a range of dc and ac electrochemical techniques to probe associative interactions of C-reactive protein (CRP) with CRP antibody (aCRP) immobilized on a gold electrode surface was investigated. It was demonstrated that the investigated electrochemical techniques can be used efficiently to probe these interactions over a wide CRP concentration range, from 1.15×10−5 to 1.15mgL−1. The measured sensitivity of the techniques is in the following decreasing order: differential pulse voltammetry, charge-transfer resistance obtained from electrochemical impedance spectroscopy (EIS), cyclic voltammetry, chronoamperometry, and double-layer capacitance deduced from EIS measurements which gave the poorest sensitivity.Measurements of kinetic parameters demonstrated that the associative interactions of CRP with the immobilized aCRP reached quasi-equilibrium after 20–30min. The kinetics of these interactions was modeled successfully using a two-step kinetic model. In this model, the first step represents reversible CRP–aCRP associative–dissociative interactions, while the second step represents the irreversible transformation of the bound CRP into a thermodynamically stable configuration. It was demonstrated that the thermodynamically stable configuration of CRP starts prevailing after 7min of interaction of CRP with the immobilized aCRP.
Keywords: C-reactive protein; Antibody–antigen interactions; Cyclic voltammetry; Differential pulse voltammetry; Chronoamperometry; Electrochemical impedance spectroscopy
ASE extraction method for simultaneous carbon and nitrogen stable isotope analysis in soft tissues of aquatic organisms by Nathalie Bodin; Hélène Budzinski; Karyn Le Ménach; Nathalie Tapie (pp. 54-60).
Since lipids are depleted in13C relative to proteins and carbohydrates, variations in lipid composition among species and within individuals significantly influence δ13C and may result in misleading ecological interpretations. Whereas lipid extraction before IRMS analysis constitutes a way of stable isotope result lipid-normalisation, such a procedure was given up because of the un-controlled effects of the methods used (i.e., “Bligh & Dyer”, Soxhlet, etc.) on δ15N. The aim of this work was to develop a simple, rapid and efficient lipid extraction method allowing for simultaneous C and N stable isotope analysis in the biological soft tissues of aquatic organisms. The goal was to be free from the lipid influence on δ13C values without interfering with δ15N values. For that purpose, the modern automated pressurized liquid extraction technique ASE (accelerated solvent extraction) was selected. Eel muscles representative of a broad range of fat contents were extracted via ASE by using different semi-polar solvents (100% dichloromethane and 80% n-hexane/20% acetone) and by operating at different temperature (ambient temperature and 100°C) and pressure (750 and 1900psi) conditions. The results were discussed in terms of lipid extraction efficiency as well as δ13C and δ15N variability.
Keywords: δ; 15; N and δ; 13; C; Accelerated solvent extraction; Fat content; Muscle; Fish
Production of immunoaffinity membranes for direct analysis of antigen after antibody separation and blotting under non-denaturing conditions by Youji Shimazaki; Azusa Kodama (pp. 61-66).
Membrane-immobilized anti-transferrin antibody, which was produced after antibody was separated using non-denaturing two-dimensional electrophoresis (2DE), was transferred to a polyvinylidene difluoride (PVDF) membrane and was stained by direct blue 71. The antigen, transferrin, specifically bound to the membrane-immobilized antibody and was eluted only after rinsing the membrane with glutamic acid or aspartic acid solution. The antigen was analyzed directly by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) when the membrane was incubated with human plasma after the removal of human serum albumin using polyethylene glycol. The transferrin extracted by glutamic acid or aspartic acid solution retained the binding of Fe3+ in the presence of the carbonate anion. We found that immunoaffinity membranes can be useful for simple and rapid removal and extraction of intact proteins after antibody separation and blotting under non-denaturing conditions.
Keywords: Abbreviations; 2DE; two-dimensional electrophoresis; PVDF; polyvinylidene difluoride; IEF; isoelectric focusing; TEMED; N,N,N′N′-tetramethylenediamine; TFA; trifluoroacetic acid; CBB; Coomassie Brilliant Blue; MALDI-TOF MS; matrix-assisted laser desorption/ionization time-of-flight mass spectrometry; Tris; 2-amino-2-hydroxymethyl-1,3-propanediolTransferrin; Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry; Fe; 3+; -binding; Non-denaturing two-dimensional electrophoresis; Immobilization; Direct blue 71 stain
Classification of red wines by chemometric analysis of voltammetric signals from PEDOT-modified electrodes by L. Pigani; G. Foca; A. Ulrici; K. Ionescu; V. Martina; F. Terzi; M. Vignali; C. Zanardi; R. Seeber (pp. 67-73).
Nine different types of Italian red wines of four different varieties were analysed, without any sample pre-treatments, by voltammetric techniques using a poly(3,4-ethylenedioxythiophene)-modified electrode. The data matrices consisting of the currents measured at different potentials, by repeated Cyclic Voltammetry or Differential Pulse Voltammetry, are submitted to chemometric analysis. After explorative tests based on Principal Component Analysis, Partial Least Squares-Discriminant Analysis classification models are built both for the training and for the test sets. To this aim, different classification strategies are adopted, considering the responses from the two techniques either separately or joined together to form a data matrix including the whole voltammetric information.
Keywords: Amperometric sensor; Electronic tongue; Conducting polymer; Red wines; Differential Pulse Voltammetry; Cyclic Voltammetry; Principal Component Analysis; Partial Least Squares-Discriminant Analysis
Nano-level monitoring of Yb(III) by fabrication of coated graphite electrode based on newly synthesized hexaaza macrocyclic ligand by Ashok K. Singh; Prerna Singh (pp. 74-82).
The two macrocyclic ligands 2,12-(2-methoxyaniline)2-4,14-Me2-[20]-1,4,11,14-tetraene-1,5,8,11,15,18-N6 (L1) and 2,12-(2-methoxyaniline)2-4,14-Me2-8,18-dimethylacrylate-[20]-1,4,11,14-tetraene-1,5,8,11,15,18-N6 (L2) have been synthesized and explored as neutral ionophores for preparing poly(vinylchloride) (PVC) based membrane sensors selective to Yb(III) ions. Effects of various plasticizers and anion excluders were studied in detail and improved performance was observed. The best performance was obtained for the membrane sensor having a composition of L2:PVC:BA:NaTPB in the ratio of 5: 40: 52: 3 (w/w; mg). The performance of the membrane based on L2 was compared with polymeric membrane electrode (PME) as well as with coated graphite electrode (CGE). The electrodes exhibit Nernstian slope for Yb3+ ions with limits of detection of 4.3×10−8M for PME and 5.8×10−9M for CGE. The response time for PME and CGE was found to be 10s and 8s, respectively. The potentiometric responses are independent of the pH of the test solution in the pH range 3.0–8.0 for PME and 2.5–8.5 for CGE. The CGE has found to work satisfactorily in partially non-aqueous media upto 30% (v/v) content of methanol, ethanol and 20% (v/v) content of acetonitrile and could be used for a period of 5 months. The CGE was used as indicator electrode in the potentiometric titration of Yb3+ ions with EDTA and in determination of fluoride ions in mouthwash samples. It can be used for determination of sulfite in red and white wine samples and also in determination of Yb3+ in various binary mixtures with quantitative results.
Keywords: Macrocyclic ligands; Ytterbium selective sensor; Polymeric membrane electrode; Coated graphite electrode
Characterization of redox polymer based electrode and electrochemical behavior for DNA detection by Filiz Kuralay; Arzum Erdem; Serdar Abacı; Haluk Özyörük; Attila Yıldız (pp. 83-89).
Characterization of redox polymer, poly(vinylferrocenium) perchlorate (PVF+ClO4−) coated as a film on Pt electrodes, and the detection of DNA based on the electrochemical behavior of the polymer were described in this study. PVF+ClO4− modified electrodes were prepared by the electrooxidation of poly(vinylferrocene) (PVF), and DNA immobilized polymer modified electrode was then prepared. The characterization of the polymer modified electrodes were performed by scanning tunneling microscopy (STM), Raman spectroscopy and alternating current (AC) impedance. The effects of DNA concentration, pH, and polymer films in various thicknesses based on the electrode response were also investigated. The electrochemical behavior of DNA modified polymer electrode by using double-stranded DNA (dsDNA) or single-stranded DNA (ssDNA) was compared. DNA hybridization was also investigated.
Keywords: Poly(vinylferrocenium) modified electrodes; Poly(vinyferrocene); STM; Raman spectroscopy; AC impedance
Immunoassay channels for α-fetoprotein based on encapsulation of biorecognition molecules into SBA-15 mesopores by Jiehua Lin; Chunyan He; Shusheng Zhang (pp. 90-94).
A novel immunoassay channeling sensor for α-fetoprotein (AFP) was proposed by incorporating biorecognition molecules into the mesopores of well-ordered hexagonal SBA-15. As the biosensing element, alkaline phosphatase (ALP)-labeled antibody was embedded into the mesopores with the substrate of 1-naphthyl phosphate (1-NP). The encapsulated ALP-labeled antibody retained its bioactivities on catalytic hydrolysis reaction with 1-NP and immunological reaction with antigen. Ionic liquid–chitosan hybrid was chosen to increase film adherence and prevent the leakage of the immobilized molecules. The peak current responses decreased due to the increasing spatial blocking and impedance from the formation of nonconductive immunoconjugates on the surface of the electrode. The experimental parameters were optimized including the concentrations of the immobilized 1-NP and ALP-labeled antibody, and the amounts of SBA-15 and ionic liquid for the electrode modification. Under the optimized conditions, the constructed immunosensor could detect AFP in a linear range from 1.0 to 150ngmL−1 with a detection limit of 0.8ngmL−1. It provided an alternative strategy for the detection of antigens or other proteins by the mesoporous materials.
Keywords: Immunosensor; Mesoporous SBA-15; α-Fetoprotein; Alkaline phosphatase; Ionic liquid
Effect of substrate and embedded metallic impurities of fullerene in the determination of nandrolone by Rajendra N. Goyal; Sanghamitra Chatterjee; Sunita Bishnoi (pp. 95-99).
A comparison of edge plane pyrolytic graphite substrate is made with other substrates like indium tin oxide, glassy carbon, gold and basal plane pyrolytic graphite as a substrate for fullerene modification for the determination of nandrolone by Osteryoung square wave voltammetry (OSWV) in phosphate buffer media. Comparative study of voltammetric response of nandrolone at untreated, purified and super-purified fullerene modified edge plane pyrolytic graphite electrode (EPPGE) is also carried out to determine the role of embedded metallic impurities of fullerene on determination of nandrolone. It is observed that EPPGE serves as best substrate among the studied for casting fullerene. The removal of embedded metals from fullerene shifts the peak potential of nandrolone to more positive potentials and peak current decreases. A linear calibration curve is obtained in the concentration range of 0.01–50nM with a detection limit and sensitivity of 1.5×10−11M and 1.838μAnM−1, respectively. The developed method was satisfactorily applied to the determination of nandrolone in several commercially available medicinal samples.
Keywords: Nandrolone; Fullerene; Metallic impurities; Pyrolytic graphite electrode
Determination of foodborne pathogenic bacteria by multiplex PCR-microchip capillary electrophoresis with genetic algorithm-support vector regression optimization by Yongxin Li; Yuanqian Li; Bo Zheng; Lingli Qu; Can Li (pp. 100-107).
A rapid and sensitive method based on microchip capillary electrophoresis with condition optimization of genetic algorithm-support vector regression (GA-SVR) was developed and applied to simultaneous analysis of multiplex PCR products of four foodborne pathogenic bacteria. Four pairs of oligonucleotide primers were designed to exclusively amplify the targeted gene of Vibrio parahemolyticus, Salmonella, Escherichia coli ( E. coli) O157:H7, Shigella and the quadruplex PCR parameters were optimized. At the same time, GA-SVR was employed to optimize the separation conditions of DNA fragments in microchip capillary electrophoresis. The proposed method was applied to simultaneously detect the multiplex PCR products of four foodborne pathogenic bacteria under the optimal conditions within 8min. The levels of detection were as low as 1.2×102CFUmL−1 of Vibrio parahemolyticus, 2.9×102CFUmL−1 of Salmonella, 8.7×101CFUmL−1 of E. coli O157:H7 and 5.2×101CFUmL−1 of Shigella, respectively. The relative standard deviation of migration time was in the range of 0.74–2.09%. The results demonstrated that the good resolution and less analytical time were achieved due to the application of the multivariate strategy. This study offers an efficient alternative to routine foodborne pathogenic bacteria detection in a fast, reliable, and sensitive way.
Keywords: Microchip capillary electrophoresis; Foodborne pathogenic bacteria; Multiplex polymerase chain reaction; Genetic algorithm-support vector regression
Characterization of synthetic polymers and speck impurities in cellulose pulp: A comparison between pyrolysis-gas chromatography–mass spectrometry and Fourier transform infrared spectroscopy by F.O. Silvério; L.C.A. Barbosa; C.R.A. Maltha; D. Piló-Veloso (pp. 108-116).
Pyrolysis-gas chromatography–mass spectrometry (Py-GC/MS) and Fourier transform infrared (FT-IR) spectroscopy were used for characterizing specks in cellulose pulp, polymeric materials and pitch formed during the cellulose extraction and paper production in the Brazilian mill. Three samples were analyzed and the pyrograms and infrared spectra obtained were compared. The results showed that the analytical pyrolysis more effectively differentiated between impurities (dirt specks) when compared to the infrared spectroscopy.
Keywords: Pyrolysis-gas chromatography–mass spectrometry; Fourier transform infrared spectroscopy; Specks in pulp; Pitch