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Analytica Chimica Acta (v.547, #2)
Chromatographic and electrophoretic procedures for analyzing plant pigments of pharmacologically interests by Xiuhua Sun; Xiurong Yang; Erkang Wang (pp. 153-157).
The achievements in the use of chromatographic and electrophoretic techniques including thin-layer chromatography, high-performance liquid chromatography and capillary electrophoresis for the separation and quantitative determination of pharmacologically interesting plant pigments in various sample matrices such as medicine, plant, foods and food products, etc. are surveyed and critically evaluated.
Keywords: Thin-layer chromatography; HPLC; Capillary electrophoresis; Plant pigments
Chromatographic evaluation of perphenylcarbamoylated β-cyclodextrin bonded stationary phase for micro-high performance liquid chromatography and pressurized capillary electrochromatography by Ailing Zhou; Xianyu Lv; Yunxuan Xie; Chao Yan; Ruyu Gao (pp. 158-164).
Application of mono (6A- N-ethylenediamine-6A-deoxy) perphenylcarbamoylated β-cyclodextrin (β-CD) bonded stationary phase (CSP) in micro-high performance liquid chromatography (micro-HPLC) and pressurized capillary electrochromatography (p-CEC) was firstly presented. A series of racemic α-amidophosphonates were resolved in reversed- and normal-phase modes on this CSP. The investigated chromatographic parameters include retention factor ( k′), separation factor ( α) and resolution ( Rs) of solutes. In addition, the structural variation of the solutes and the experimental factors affecting chiral separations have been examined, including the percentage of alcohol modifier, the linear velocity ( u) of the mobile phase, electrical field strength, etc. Baseline separation was achieved for most of the entities. Hydrophobic interaction, steric effect and π–π interaction contribute to the possible mechanism. Comparative results indicate that higher Rs value up to 3.1 was found in micro-HPLC, higher efficiency up to 29,970 in p-CEC.
Keywords: Chiral stationary phase (CSP); Perphenylcarbamoylated β-cyclodextrin; α-Aminophosphonate; Micro-high performance liquid chromatography; Pressurized capillary electrochromatography
Ionic liquids as additives for separation of benzoic acid and chlorophenoxy acid herbicides by capillary electrophoresis by Lijun Yu; Weidong Qin; Sam Fong Yau Li (pp. 165-171).
Ionic liquids (ILs) were tested as additives to phosphate–acetate buffer for the separation of chlorophenoxy and benzoic herbicide acids. The effects of buffer concentration, buffer pH, IL concentration, and concentration of organic solvent were investigated. It was found that in the presence of 40mM phosphate–acetate containing 10% acetonitrile at pH 4.5, addition of 10mM 1-butyl-3-methylimidazoium could reverse EOF. The shoulder-merged peaks of two herbicide acids, 2,4-dichlorobenzoic acid and 3,5-dichlorobenzoic acid, were successfully resolved by the addition of IL cation. Apart from these, results showed different IL cations had different influences on the migration behavior of some of the analytes, while IL anions did not lead to obvious difference on the separation.
Keywords: Abbreviations; IL; ionic liquid; BMIM; 1-butyl-3-methylimidazolium; EMIM; 1-ethyl-3-methylimidazolium; HMIM; 1-hexyl-3-methylimidazolium; HBMIM; 1-(4-hydroxy-butyl)-3-methylimidazoliumIonic liquid; Herbicide; Capillary electrophoresis
Reduction of silanophilic interactions in liquid chromatography with the use of ionic liquids by Michał Piotr Marszałł; Tomasz Bączek; Roman Kaliszan (pp. 172-178).
A suppression of silanophilic interactions by the selected ionic liquids added to the mobile phase in thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC) is reported. Acetonitrile was used as the eluent, alone or with various concentrations of water and phosphoric buffer pH 3. Selectivity of the normal (NP) and the reversed (RP) stationary phase material was examined using a series of proton-acceptor basic drugs analytes. The ionic liquids studied appeared to significantly affect analyte retention in NP-TLC, RP-TLC and RP-HPLC systems tested. Consequently, the increased separation selectivity was attained. Due to ionic liquid additives to eluent even analytes could be chromatographed, which were not eluted from the silica-based stationary phase materials with 100% of acetonitrile in the mobile phase. Addition of ionic liquid already in very small concentration (0.5%, v/v) could reduce the amount of acetonitrile used during the optimization of basic analytes separations in TLC and HPLC systems. Moreover, the influence of temperature on the separation of basic analytes was demonstrated and considered in practical HPLC method development.
Keywords: Ionic liquids; Liquid chromatography; Suppression of silanophilic interactions
Evaluation of microstructural features of a new polymeric organic stationary phase grafted on silica surface: A paradigm of characterization of HPLC-stationary phases by a combination of suspension-state1H NMR and solid-state13C-CP/MAS-NMR by Hamid R. Ansarian; Mahnaz Derakhshan; M. Mizanur Rahman; Toshihiko Sakurai; Makoto Takafuji; Isao Taniguchi; Hirotaka Ihara (pp. 179-187).
Silica-supported poly(octadecylacrylate) (Sil-ODA n), polymeric octadecylsilyl silica (polymeric ODS), and monomeric octadecylsilyl silica (monomeric ODS) were studied by a combination of suspension-state1H NMR and solid-state13C CP/MAS-NMR to probe the mechanisms underlying their functions as stationary phases for RP-HPLC. Sil-ODA n, with a strong temperature dependent separation behaviour showed correspondent temperature dependent manifestations in both suspension-state1H NMR and solid-state13C CP/MAS-NMR experiments. With a gradual increase in temperature, intensity of proton signals (1H NMR) of octadecyl moieties (mainly methylene groups) rose dramatically. This dramatic rise was at the same temperature of an endothermic peak detectable in its DSC thermogram indicating a relatively complete solid to liquid phase transition. In addition temperature dependencies of the ratio of trans to gauche conformed well to temperature dependencies of the separation factor between naphthacene and triphenylene (as a simple indicator of shape selectivity). Therefore NMR spectra of Sil-ODA n were used as a reference for ascertaining percentage of octadecyl moieties of liquid type mobility in the two other stationary phases. Using this method we determined percentage of liquid phase in polymeric ODS and monomeric ODS at various temperatures. We suggest a combination of suspension-state1H NMR and solid-state13C CP/MAS-NMR for structure-dynamic characterization of various kinds of hydrocarbon chains grafted onto the silica particles.
Keywords: Liquid chromatography; Molecular-shape selectivity for PAHs; Comb-shaped polymer; Alkyl chain conformation; Suspension-state NMR spectroscopy
A comparative study of diesel analysis by FTIR, FTNIR and FT-Raman spectroscopy using PLS and artificial neural network analysis by Vianney O. Santos Jr.; Flavia C.C. Oliveira; Daniella G. Lima; Andrea C. Petry; Edgardo Garcia; Paulo A.Z. Suarez; Joel C. Rubim (pp. 188-196).
Diesel properties determined by ASTM reference methods as cetane index, density, viscosity, distillation temperatures at 50% (T50) and 85% (T85) recovery, and the total sulfur content (%, w/w) were modeled by FTIR-ATR, FTNIR, and FT-Raman spectroscopy using partial last square regression (PLS) and artificial neural network (ANN) spectral analysis. In the PLS models, 45 diesel samples were used in the training group and the other 45 samples were used in the validation. In the ANN analysis a modular feedforward network was used. Sixty diesel samples were used in the neural network training and other 30 samples were used in the validation. Two different ATR configurations were compared in the FTIR, a conventional (ATR1) and an immersion (ATR2) cell. The ATR1 cell presented the best results, with smaller prediction errors (root mean square error of prediction, RMSEP). The comparison of the three PLS models (FTIR-ATR1, FTNIR, and FT-Raman) shows that reasonable values of R2 and RMSEP were obtained by the FTIR-ATR1 and FTNIR models in the evaluation of density, viscosity, and T50. The PLS/FT-Raman models presented reasonable results only for the T50 property. None of the techniques was able to generate suitable PLS calibration models for the determination of sulfur content. The ANN/FT-Raman models presented the best performances, with all models presenting R2-values above 85% some of them with RMSEP values significantly smaller than those obtained with FTIR-ATR and FTNIR. The ANN/FT-Raman and ANN/FTIR-ATR1 models were able to estimate the total sulfur content of diesel with 0.01% (w/w) accuracy.
Keywords: FTIR; FTNIR; FT-Raman; PLS; Artificial neural network; Diesel
Solid-phase FT-Raman determination of caffeine in energy drinks by Sergio Armenta; Salvador Garrigues; Miguel de la Guardia (pp. 197-203).
A solid-phase vibrational spectrometry-based methodology (solid-phase Fourier transform-Raman spectrometry, SP-FT-Raman) has been developed for caffeine determination in commercial energy drink samples. The Raman spectra of caffeine, fixed on a C18 solid phase packed into a glass tube of 5mm i.d., was obtained directly between 3500 and 70cm−1. In order to quantify caffeine, Raman intensity between 573 and 542cm−1 corrected using a baseline defined between 580 and 540cm−1 was used. A repeatability of 3%, as relative standard deviation of five analysis of a 200mgl−1 concentration, and a limit of detection of 18mgl−1 were obtained. The SP-FT-Raman procedure provides a sampling frequency of 13.3h−1, higher than that of liquid chromatography (LC), which was 7.0h−1. The use of FT-Raman reduces the reagent consumption and waste generation, also minimizing the sample handling. Results obtained by the developed procedure were statistically comparable with those found by a reference LC method.
Keywords: Caffeine; Energy drink; FT-Raman; Solid phase
A clean method for flow injection spectrophotometric determination of cyclamate in table sweeteners by Fábio R.P. Rocha; Eva Ródenas-Torralba; Ángel Morales-Rubio; Miguel de la Guardia (pp. 204-208).
A flow system based on the multicommutation is proposed for fast and clean determination of cyclamate. The procedure exploits the reaction of cyclamate with nitrite in acidic medium and the spectrophotometric determination of the excess of nitrite by iodometry. The flow system was designed with a set of solenoid micro-pumps to minimize reagent consumption and waste generation. The detection limit was estimated as 30μmolL−1 (99.7% confidence level) with linear response ranging up to 3.0mmolL−1. The coefficient of variation was estimated as 1.7% for a solution containing 2.0mmolL−1 cyclamate ( n=20). About 60 samples can be analyzed per hour, consuming only 3mg KI and 1.3μg NaNO2, and generating 2.0mL of effluent per determination, thus providing an environmentally friendly alternative to previously proposed procedures. Common artificial and natural sweeteners did not interfere when present in concentrations 10-times higher than cyclamate. The procedure was successfully applied for determination of cyclamate in artificial table sweeteners with results in agreement with the reference method at the 95% confidence level.
Keywords: Flow injection; Multicommutation; Solenoid pumps; Spectrophotometry; Cyclamate; Artificial sweeteners
Biosensor based on platinum chips for glucose determination by M. Asunción Alonso Lomillo; Javier Gonzalo Ruiz; F. Javier Muñoz Pascual (pp. 209-214).
Amperometric glucose biosensors based on a Pt microelectrode chip are described. Horseradish peroxidase (HRP) and glucose oxidase (GOX) were co-immobilized on a platinum microelectrode by electropolymerization. Two different compounds, namely ferrocyanide (Fe) and meldola's blue (MB), were used as mediators to transfer electrons between the enzymes and the electrode. Experimental variables were optimised using experimental design methodology, by a 23 central composite design, taking the intensity registered for a given glucose solution as response. Given the reproducibility (residual standard deviation (R.S.D.), 9.122% with n=3) and repeatability (R.S.D., 7.095% with n=4) reached by the Fe-based microbiosensor under the optimum conditions, the analysis of glucose in grape juice, 319.46gl−1±37.12 ( n=3 and α=0.05), was successfully accomplished.
Keywords: Microsystem technologies; Microbiosensors; Glucose; Electropolymerization; Experimental design
A novel fluorescence probe for cilnidipine assay by Shuzhen Tan; Jianhui Jiang; Guangyu Shen; Guoli Shen; Ruqin Yu (pp. 215-220).
A general route for preparation of dye-encapsulated polymer particles via an emulsion polymerization process has been described. 1-Naphthaleneboronic acid (NBA) was encapsulated, the resultant particles were used as a fluorescence probe for cilnidipine assay based on fluorescence quenching. The sensitivity of NBA-encapsulated probe to cilnidipine was largely improved in comparison with that of free NBA. The probe showed a linear response toward cilnidipine over the concentration range of 2.0×10−7 to 1.1×10−5moll−1, with high sensitivity, fast response time, and good selectivity.
Keywords: 1-Naphthaleneboronic acid; Fluorescence probe; Cilnidipine; Emulsion polymerization; Polymer particles
A ratiometric fluorescence halide sensor based on covalently immobilization of quinine and benzothioxanthene by Cheng-Gang Niu; Ai-Ling Guan; Guang-Ming Zeng; Yun-Guo Liu; Guo-He Huang; Pan-Feng Gao; Xiao-Qin Gui (pp. 221-228).
A new fluorescence chemical sensor for the determination of Cl−, Br− and I− has been successfully demonstrated. The membrane contains two fluorophores that display two largely different response spectra. The first fluorophore, N-(2-methacryloxyethyl) benzo[k,l]thioxanthene-3,4-dicarboximide (MBTD, benzothioxanthene derivative), used as reference was halide-insensitive. The second fluorophore, quinine sulphate, used as sensitive carrier was halide-quenchable. Both were co-polymerized with acrylamide, hydroxyethyl methacrylate and triethylene glycol dimethacrylate onto glass surface. The fluorescence intensity of quinine decreased with increasing of halide concentration due to dynamic quenching, but the fluorescence intensity of MBTD was almost not affected by halide. Under these conditions, the halide-dependent fluorescence intensity of quinine was converted into a ratio of the two fluorescence intensities, which were expressed as a function of halide concentration. Satisfactory reproducibility, reversibility and a short response time were realized. The sensor also showed good selectivity, common ions and some organic species did not interfere with the measurement of halide. With the optimum membrane described, detection limits were of 2.2×10−4, 7.5×10−5 and 6.2×10−5molL−1 for Cl−, Br− and I−, respectively. The proposed method was applied to the determination of halide in earth samples. The sensing membrane was found to have a lifetime at least 2 months.
Keywords: Fluorescence sensor; Halide; Covalent immobilization; Ratiometric; Quinine sulphate; Benzothioxanthene
Biosensor discrimination of meat juice from various animals using a lectin panel and ellipsometry by Jenny Carlsson; Fredrik Winquist; Bengt Danielsson; Ingemar Lundström (pp. 229-236).
In this work, simple microcontact printed gold-wafers were used to make a lectin panel for investigation and discrimination of different meat juices from fresh meat of cattle, chicken, pig, cod, turkey and lamb. Seven different lectins were thus attached to gold surfaces using the streptavidin–biotin method. Lectins recognize and bind specifically to carbohydrate structures present on different proteins. The biorecognition was evaluated with null ellipsometry and the data obtained was related to an internal standard of lactoferrin. The data was evaluated with multivariate data analysis techniques to identify possible discrimination or grouping of data. Scanning ellipsometry was used for visualization of the binding pattern of the lectins and the meat juice proteins. The two-dimensional images obtained could be used to visualize the protein distribution, furthermore, to exclude anomalies. The results showed that the different meat juices from the six different species: cattle, chicken, pig, cod, turkey and lamb could be discriminated from each other. The results showed to be more repetitive for the mammalian meat juices. Using a simple model based on an artificial neuronal net, it was also possible to classify meat juices from the mammals investigated.
Keywords: Lectin panel; Ellipsometry; Meat juice; Multivariate data analysis
Determination of arsenic(III) and total inorganic arsenic in water samples using an on-line sequential insertion system and hydride generation atomic absorption spectrometry by Aristidis N. Anthemidis; George A. Zachariadis; John A. Stratis (pp. 237-242).
A simple and robust on-line sequential insertion system coupled with hydride generation atomic absorption spectrometry (HG-AAS) was developed, for selective As(III) and total inorganic arsenic determination without pre-reduction step. The proposed manifold, which is employing an integrated reaction chamber/gas–liquid separator (RC-GLS), is characterized by the ability of the successful managing of variable sample volumes (up to 25ml), in order to achieve high sensitivity. Arsine is able to be selectively generated either from inorganic As(III) or from total arsenic, using different concentrations of HCl and NaBH4 solutions. For 8ml sample volume consumption, the sampling frequency is 40h−1. The detection limit is cL=0.1 and 0.06μgl−1 for As(III) and total arsenic, respectively. The precision (relative standard deviation) at 2.0μgl−1 ( n=10) level is sr=2.9 and 3.1% for As(III) and total arsenic, respectively. The performance of the proposed method was evaluated by analyzing the certified reference material NIST CRM 1643d and spiked water samples with various concentration ratios of As(III) to As(V). The method was applied for arsenic speciation in natural waters samples.
Keywords: Arsenic speciation; Hydride generation atomic absorption spectrometry; Sequential; Gas–liquid separator
Polycyclic aromatic hydrocarbon analysis in different matrices of the marine environment by Anna Filipkowska; Ludwik Lubecki; Grażyna Kowalewska (pp. 243-254).
Polycyclic aromatic hydrocarbons (PAHs) were determined in marine samples of various types, i.e. seawater, sediment and mussel homogenate samples. The samples were spiked with standard PAH mixtures in both polar (acetonitrile) and non-polar ( i-octane) solvents, then extracted. Extraction from seawater was performed by liquid/liquid extraction to hexane (LLE) and with solid phase extraction (SPE) discs. The water samples were filtered and unfiltered seawater, and redistilled water for comparison. The discs with PAHs adsorbed from water samples, and also the sediment and mussel homogenate samples, were extracted with acetonitrile by sonication. PAHs in the disc extracts and from the LLE were cleaned-up using TLC and next determined by GC/MS/IT (with ion-trap) and HPLC-DAD/UV. The analytical procedures were verified with deuterated PAH standard mixtures. The large differences in PAH recoveries (from 12 to 86% for sum, and from 3 to 135% for particular PAHs) do not depend solely on the type of matrix and analytical procedure applied (e.g. standard solvent, volume of evaporated sample), but also on the concentration and molecular structure of the analyte. Usually, only a fraction of each PAH content in the matrix is determined, depending on the particulate matter in seawater and the sorption properties of the solid matrix. The recoveries of deuterated PAHs are higher than those of non-deuterated compounds.
Keywords: PAH analysis; Marine sediments; Seawater; Mussels
Selective recovery and preconcentration of mercury with a benzoylthiourea-solid supported liquid membrane system by Clàudia Fontàs; Manuela Hidalgo; Victòria Salvadó; Enriqueta Anticó (pp. 255-261).
In the present study, the compound N-benzoyl- N′, N′-diheptadecylthiourea has been evaluated as carrier for the extraction of toxic metals. Liquid–liquid extraction experiments of Hg(II), Cd(II) and Pb(II) in nitrate media were performed, and neither cadmium nor lead were extracted in the pH range from 2 to 6, showing benzoylthiourea derivative as a high selective extractant for mercury.A solid supported liquid membrane system has been developed for mercury permeation using 0.3M thiourea as stripping agent. Several parameters affecting liquid membrane performance are evaluated, such as the organic solvent, where the best results are obtained with a mixture decaline:cumene, the feed composition and the length of alkyl chains in the carrier. The choice of the polymeric support material used to contain the liquid membrane, as well as its physical characteristics, was found to be crucial to ensure an effective metal transport across the liquid membrane.The application of this SLM in hollow fiber supported liquid membrane (HFSLM) configuration allowed the enrichment of solutions with low mercury content. High preconcentration factors are obtained, showing the feasibility of using the developed system as an effective technique for analytical applications.
Keywords: Mercury; Benzoylthiourea; Supported liquid membrane; Polymeric support; Hollow fiber
A multi-residue cation-exchange clean up procedure for basic drugs in produce of animal origin by George Stubbings; Jonathan Tarbin; Andrew Cooper; Matthew Sharman; Tim Bigwood; Paul Robb (pp. 262-268).
There is considerable interest in maximising the amount of information obtained from animal product analyses, when screening for the presence of veterinary drug residues. One of the barriers to effective multi-residue analysis to date has been a lack of effective clean up procedures to isolate a wide range of residues from the potential interferents, which may be present in both simple and complex (including processed) foods. A cation-exchange clean up has, therefore, been developed for use with acetonitrile extracts of foods, when analysing for several basic drug groups (sulfonamides, benzimidazoles, levamisole, nitroimidazoles, tranquillisers and fluroquinolones). The clean up procedure has also been shown to be effective using a modified extraction solvent for malachite green and leucomalachite green in fish.Several of the key parameters that influence analyte recovery have been investigated and in an optimised procedure, tissue/biofluid samples containing sulfonamides, benzimidazoles, levamisole, nitroimidazoles, tranquillisers and fluoroquinolones are first extracted with acetonitrile. The extract is then dried with sodium sulfate and acidified with glacial acetic acid before loading onto a Bond Elut, strong cation-exchange (SCX) solid phase extraction (SPE) cartridge. Extracts from fish containing malachite green and leucomalachite green can be cleaned up using the same SCX SPE procedure following extraction with citrate buffer/acetonitrile. Typical recoveries of drugs from low level fortified tissues using the optimised procedure lie in the range 53–104% with the exception of carazolol from pig kidney (31%), malachite green from trout (42–51%) and ciprofloxacin from chicken muscle (44%) and from egg (21%).
Keywords: Benzimidazoles; Sulphonamides; Tranquillizers; Fluoroquinolones; Nitroimidazoles; Levamisole; Malachite green; Leucomalachite green; Multi-residue analysis; Cation-exchange; Solid phase extraction