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Analytical and Bioanalytical Chemistry (v.370, #4)
Modification and characterization of artificially patterned enzymatically active surfaces by scanning electrochemical microscopy by Gunther Wittstock (pp. 303-315).
This review summarizes the characterization of localized enzymatic activity by scanning electrochemical microscopy (SECM). After introducing the concepts of feedback imaging and generator-collector experiments with enzyme-modified solid surfaces, a comparison of the merits and limitations of both approaches is given and further illustrated by selected applications. They include enzyme-modified patterned monolayers, enzyme-modified polymer microstructures and enzyme-modified metal microstructures. Such configurations are important for the development of miniaturized bioanalytical systems with proteins, such as miniaturized enzyme electrode arrays. SECM has emerged as an ideal tool for prototyping of such systems. It also offers several mechanisms for local surface modifications under conditions compatible with conservation of protein functionality of enzymes and antibodies. The subsequent imaging of the immobilized activity provides direct information about local immobilized enzyme activity. The range of biotechnological applications can be expanded by labeling other biomolecules, such as monoclonal antibodies, with appropriate enzymes. Miniaturized electrochemical enzyme immunoassays that apply the sandwich format and SECM as the detection method are reviewed. They have been performed on microstructured supports after reagent spotting or on agglomerates of surface-modified magnetic microbeads. Finally, current challenges are listed with indications of ongoing research to overcome current limitations by means of instrumental improvements.
Separation of metal ions by capillary electrophoresis – diversity, advantages, and drawbacks of detection methods by C. Vogt; Gregory L. Klunder (pp. 316-331).
Capillary electrophoresis (CE) has been applied to metal-ion analysis during the last 10 years. To improve sensitivity and selectivity different modes of detection have been adapted or developed. The selection of commercially available detection systems for metal-ion analysis is still primarily limited to UV–Vis detection, although other commercial systems, e.g. fluorescence, conductivity, or interfaces for coupling to mass spectrometry (MS) or inductively coupled plasma mass spectrometry (ICP–MS) are becoming available. High demands are made on any detector used in CE, because the analytical signal has to be extracted from less than 1 nL of sample, which corresponds to a total amount of ≤ 10–12 to 10–15 mol analyte. This paper compares currently available and recently developed detection methods for CE as applied to the analysis of metal ions. Commercially available techniques, for example UV– Vis, fluorescence, or mass spectrometry, and other new detection methods including electrochemistry, radioactivity, and XRF, are discussed and future trends are anticipated.
Laser ablation – reflections on a very complex technique for solid sampling by Kay Niemax (pp. 332-340).
This paper is an attempt to point out the complex correlations between the experimental conditions in solid sampling by lasers. In particular, the influence of the laser properties, the surrounding gas, and the matrix on the analytical results of laser ablation techniques, such as laser induced breakdown spectrometry or laser ablation–ICP–MS, will be discussed.
Self-absorption effects in radially and axially viewed inductively coupled plasma-atomic emission spectrometry – the key role of the operating conditions by Matthieu Chausseau; Emmanuelle Poussel; J.-M. Mermet (pp. 341-347).
Self-absorption effects leading to curvatures of the upper part of calibration graphs were investigated in multichannel detection ICP–AES. A dual view Optima 3000 ICP system was used to enable the simultaneous determination of 38 lines for both radial and axial viewing. Resonance and non-resonance lines were selected for both atomic and ionic lines. The concentrations of 22 standards were in the range 0.1–100 mg L–1 and two sets of operating conditions, namely power and carrier gas flow rate, were used to evaluate their influence. It was found that these two conditions, and in particular the carrier gas flow rate, play a major role in self-absorption effects. Except for strongly absorbing lines, it was possible, under suitable conditions, to reduce or to suppress differences between self-absorption effects in radial and axial viewing, enabling extension of the range of linearity of axial viewing to higher concentrations. A diagnostic tool, based on emission line ratios, is proposed for detection of self-absorption. A calibration procedure is given for strongly absorbing lines affected by self-absorption even when operating conditions were optimized.
Role of electronegativity in the qualitative inference of the TOF–SIMS fragment pattern of inorganic compounds by K. Hirokawa; Z. Li; A. Tanaka (pp. 348-357).
The role of the electronegativity of atoms in inorganic compounds in TOF–SIMS fragmentation is discussed. From a study of approximately 30 inorganic compounds – chlorides, oxides, nitrates, and sulfates – a simple rule has been proposed for the dependence of fragment pattern appearance on the electronegativity (electron affinity), which can be easily obtained from handbooks, and the valence of positive and negative ions in these compounds. TOF–SIMS measurements of metal and alloy surfaces, should be corrected for the ionization potentials and/or electronegativities of atoms present in surface contaminants.
An interlaboratory study to test instrument performance of hydrogen dual-inlet isotope-ratio mass spectrometers by W. A. Brand; T. B. Coplen (pp. 358-362).
An interlaboratory comparison of forty isotope-ratio mass spectrometers of different ages from several vendors has been performed to test 2H/1H performance with hydrogen gases of three different isotopic compositions. The isotope-ratio results (unsufficiently corrected for H3 + contribution to the m/z = 3 collector, uncorrected for valve leakage in the change-over valves, etc.) expressed relative to one of these three gases covered a wide range of values: –630‰ to –790‰ for the second gas and –368‰ to –462‰ for the third gas. After normalizing the isotopic abundances of these test gases (linearly adjusting the δ values so that the gases with the lowest and highest 2H content were identical for all laboratories), the standard deviation of the 40 measurements of the intermediate gas was a remarkably low 0.85‰. It is concluded that the use of scaling factors is mandatory for providing accurate internationally comparable isotope-abundance values. Linear scaling for the isotope-ratio scales of gaseous hydrogen mass spectrometers is completely adequate.
New cyclodextrin derivatives as chiral selectors in capillary electrophoresis by V. Cucinotta; Alessandro Giuffrida; Giulia Grasso; Giuseppe Maccarrone; Antonino Mazzaglia; Graziella Vecchio (pp. 363-366).
The separation of three pairs of enantiomeric herbicides has been successfully achieved by capillary electrophoresis at two different pH values in the presence of cyclodextrin derivatives previously synthesized in our laboratory. Two of these derivatives constitute a new class of receptor, the hemispherodextrins, in which a trehalose capping moiety is bonded to β-cyclodextrin. Because of their peculiar structure hemispherodextrins have very promising characteristics and the low receptor concentration required to achieve separation deserves particular interest.
Experimental verification of the properties of ion-selective electrodes for low concentration determination by T. Sokalski; Iwona Bedlechowicz; M. Maj-Zurawska; Adam Hulanicki (pp. 367-370).
The influence of several ion-selective electrode properties on electrode response and selectivity at low concentration levels has been investigated experimentally. The properties investigated were the composition of inner electrode solution, the composition of the membrane, the presence of interfering ions in the sample, and the thickness of diffusion layer in the sample solution. All the results obtained confirmed theoretical considerations.
Thin-layer chromatographic behavior of rare earths on silica gel with aqueous alkaline earth metal nitrate solutions as mobile phases by Yoichi Takeda; K. Ishida (pp. 371-376).
The TLC behavior of all the rare earths except Pm has been surveyed on silica gel (pH 7.0) pretreated with 0.1 mol L–1 tris(hydroxymethyl)aminomethane and 0.1 mol L–1 HCl with aqueous nitrate solutions of alkaline earth metals as mobile phases. The RF values of the lanthanides varied in a regular and characteristic way accompanied by the tetrad effect with increasing atomic number, and when the mobile phases were changed the RF values of each metal decreased in the order Mg2+ > Ca2+ > Sr2+ > Ba2+, as the crystal ionic radii of the alkaline earth metals increased. This adsorption sequence was not observed with alkali metal nitrate and alkali metal chloride mobile phases. A brief discussion concerning the effect on RF values of the solvent cations and the adsorption mechanism is included; also presented are typical chromatograms for the separation of multi-component mixtures containing adjacent lanthanides.
Quinalizarin anchored on Amberlite XAD-2. A new matrix for solid-phase extraction of metal ions for flame atomic absorption spectrometric determination by Manjeet Kumar; D. P. S. Rathore; Ajai K. Singh (pp. 377-382).
Amberlite XAD-2 has been functionalized by coupling it to quinalizarin [1,2,5,8-tetrahydroxyanthraquinone] by means of an -N = N- spacer. Elemental analysis, thermogravimetric analysis, and infrared spectra were used to characterize the resulting new polymer matrix. The matrix has been used to preconcentrate Cu(II), Cd(II), Co(II), Pb(II), Zn(II), and Mn(II) before their determination by flame atomic absorption spectrometry (FAAS). UO2(II) has been preconcentrated for fluorimetric determination. The optimum pH values for maximum adsorption of the metals are between 5.0 and 7.0. All these metal ions are desorbed (recovery 91–99%) with 4 mol L–1 HNO3. The adsorptive capacity of the resin was found to be in the range 0.94–5.28 mg metal g–1 resin and loading half-life (t1/2) between 5.3 and 15.0 min. The effects of NaF, NaCl, NaNO3, Na2SO4, Na3PO4, Ca(II), and Mg(II) on the adsorption of these metal ions (0.2 μg mL–1) are reported. The lower limits of detection for these metal ions are between 1 and 15.0 μg L–1. After enrichment on this matrix flame AAS has been used to determine these metal ions (except the uranyl ion) in river water samples (RSD ≤ 6.5%); fluorimetry was used to determine uranyl ion in well water samples (RSD ≤ 6.3%). Cobalt from pharmaceutical vitamin tablets was preconcentrated by use of this chelating resin and estimated by FAAS (RSD ∼ 4%).
PbO2-based graphite–epoxy electrode for potentiometric determination of acids and bases in aqueous and aqueous–ethanolic media by Marcos F. S. Teixeira; Luiz A. Ramos; Orlando Fatibello-Filho; É. T. G. Cavalheiro (pp. 383-386).
The construction and analytical evaluation of a PbO2-based graphite–epoxy electrode sensitive to H3O+, based on incorporation of lead(IV) oxide in a graphite– epoxy matrix, are described. The data obtained from a variety of acid–base titrations in aqueous and aqueous– ethanolic media were compared with those obtained by use of a glass electrode under the same conditions. The proposed electrode provides a linear response in the pH range from 1 to 11 with a slope of –58.7 ± 0.3 mV pH–1 and –60.8 ± 0.2 mV pH–1 in aqueous and ethanolic media, respectively. The response time was less than 15 s and the lifetime of the electrode was at least eight months (ca. 5000 determinations) and its performance is good in pH determination and end-point detection in potentiometric acid–base titrations in both aqueous and aqueous– ethanolic media.
Calibration graphs for steels by IR laser ablation inductively coupled plasma atomic emission spectrometry by V. Kanický; Vítëzslav Otruba; Karel Novotný; Petr Musil; Jean-Michel Mermet (pp. 387-392).
Infrared laser ablation (IRLA) was studied as a sample-introduction technique for the analysis of steels by inductively coupled plasma atomic emission spectrometry (ICP–AES). A comparison of two IRLA–ICP–AES systems based on Q-switched nanosecond Nd : YAG lasers was performed. The beam of the Lina-Spark atomizer (LSA Sarl, Cully, Switzerland) based on the Surelite I-20 laser (Continuum, USA) was moved along a circle. A Perkin–Elmer Optima 3000 DV ICP system was used both with lateral and axial viewing modes. A laboratory-made ablation system based on the Brilliant laser (Quantel) was coupled to a Jobin-Yvon 170 Ultrace ICP (lateral viewing, polychromator part employed). A sample was rotated along a circle during ablation. Linearity of calibration plots was verified at least up to 19% Cr and 12% Ni without internal standardization for both LA–ICP–AES systems. Other elements examined were Mo up to 3%, Mn up 1.5%, Si up to 1.7%, and Cu up to 0.15%. The reproducibility was in the range 5–1 %RSD for a mass percentage 0.5–20% of steel constituents. The relative uncertainty of the centroids of the calibration lines was in the range from ± 4% to ± 12% for Cr, Ni, Mn, Mo, and Si, and from ± 8% to ± 19% for Cu. The lowest determinable quantities were calculated for calibration dependencies. Performances of both the IR-LA–ICP–AES were comparable.
A quartz crystal microbalance sensor for the detection of formic acid vapors by C. García-Verdugo-Caso; J. L. Hidalgo-Hidalgo-de-Cisneros; I. Naranjo-Rodríguez; D. Bellido-Milla (pp. 393-398).
A new quartz crystal microbalance sensor is developed to determine formic acid at low concentrations. Four previously selected polymers with acid–base characteristics were tested as possible coatings. Polyoxyethylene bis [amine] presented the best results. The sensor is rapid, sensitive [0.67 Hz/(mg/m3)], and reversible at low concentrations. The detection limit for formic acid (7.2 mg/m3) is comparable with the short term exposure limit and the threshold limit values. It presents a fast mechanical response to pressure changes, so that it can be quickly used in different environments and situations. The sensor also shows a good stability in a temperature range typical of work atmospheres (16–36 °C). It has a wide linear range (7.2–911.2 mg/m3) and a long useful time. It is also applicable to other low molecular mass carboxylic acids such as acetic acid.
Determination of inorganic acids by ion chromatography with n-tetradecylphosphocholine (zwitterionic surfactant) as the stationary phase and pure water as the mobile phase by Wenzhi Hu; Kiyoshi Hasebe; Kazuhiko Tanaka; James S. Fritz; Soichi Inoue; Masashi Ozeki (pp. 399-402).
A new ion chromatographic (IC) system, in which n-tetradecylphosphocholine (TDPC, a phosphobetaine type of zwitterionic surfactant) was used as the stationary phase, pure water as the mobile phase, and conductivity as the method of detection, has been developed for the determination of inorganic acids. Five model acids, HCl, HNO3, HClO4, H2SO4, and H3PO4, were separated to baseline and eluted in the order H3PO4 > HCl > HNO3 > H2SO4 > HClO4. When peak areas were plotted against the concentrations of the acids in samples, linear calibration curves were obtained. Ultimate determination limits were approximately 1 mmol L–1, but the discrimination of the method between solutions of different concentration was better than 10 μmol L–1 for those model analytes. Salts of divalent cations could also be separated, but they were eluted faster than the acids. No separation was observed for the salts of monovalent cations. This newly proposed approach is applicable to the simultaneous determination of the inorganic acids (produced by reactions of NOx, SOx, and HCl with water) in aerosols.
High performance liquid chromatographic determination of diazinon, permethrin, DEET (N, N-diethyl-m-toluamide), and their metabolites in rat plasma and urine by Agel W. Abu-Qare; M. B. Abou-Donia (pp. 403-407).
A rapid method was developed for the analysis of the insecticide (A) diazinon (O,O-diethyl O-2-isopropyl-6-methylpyridimidinyl) phosphorothioate, its metabolites (B) diazoxon (O,O-diethyl O-2-isopropyl-6-methylpyridimidinyl) phosphate, and (C) 2-isopropyl-6-methyl-4-pyrimidinol, the insecticide (D) permethrin [3-(2,2-dichloro-ethenyl)-2,2-dimethylcyclopropanecarboxylic acid (3-phenoxyphenyl)methylester], its metabolites (E) m-phenoxybenzyl alcohol, and (F) m-phenoxybenzoic acid, the insect repellent (G) DEET (N,N-diethyl-m-toluamide), and its metabolites (H) m-toluamide and (I) m-toluic acid in rat plasma and urine. The method is based on using C18 Sep-Pak cartridges (Waters Corporation, Milford, Mass., U.S.A.) for solid phase extraction and high performance liquid chromatography with a reversed phase C18 column, and absorbance detection at 230 nm for compounds A, B, and C, and at 210 nm for compounds D–I. The compounds were separated using a gradient from 1% to 99% acetonitrile in water (pH 3.0) at a flow rate ranging between 1 and 1.7 mL/min in a period of 17 min. The limits of detection were ranged between 20 and 100 ng/mL, while limits of quantification were 80–200 ng/mL. The relationship between peak areas and concentration was linear over a range of 100–1000 ng/mL. This method was applied to determine the above insecticides and their metabolites following dermal administration in rats.
Determination of ultratrace dissolved arsenite in water – selective coprecipitation in the field combined with HGAFS and ICP–MS measurement in the laboratory by J. T. van Elteren; Zdenka Šlejkovec; Marta Svetina; Andrej Glinšek (pp. 408-412).
Because stabilization of arsenite in water samples during transit and storage is troublesome, this work deals with a method to prevent this by on-site selective coprecipitation of arsenite with dibenzyldithiocarbamate and recovery of the coprecipitate by filtration through a 0.45-μm membrane filter. In the laboratory arsenic on the filter is quantitatively released by oxidation of arsenite to arsenate with H2O2 (6%) in alkaline medium (8 mmol L–1 NaOH) at elevated temperature (85 °C) for 30 min followed by ultratrace determination by routine HGAFS and ICP–MS. It is shown that arsenate contamination of the coprecipitate is so low that arsenate concentrations three orders of magnitude higher than the arsenite concentration do not interfere; this is essential, because arsenate is usually the dominant arsenic species in water. Because significant preconcentration can be achieved in the solution obtained from the leached filter (normally a factor 20 but easily increased to 100) very low detection limits can be obtained (only limited by the purity of the materials and the cleanliness of working); a realistic limit of determination is 0.01 μg L–1 arsenite. The procedure was used for the determination of arsenite in two ground waters from an ash depository site in the Šalek valley (Slovenia). The matrix contained some elements at very high levels but this did not impair the efficiency of arsenite coprecipitation. The results obtained by use of HGAFS and ICP–MS were not significantly different at the 5% level for sub-μg L–1 arsenite concentrations.
Heterogeneity and lability of Pb(II) complexation by humic substances: practical interpretation tools by M. Filella; Raewyn M. Town (pp. 413-418).
The complexation of Pb(II) by natural organic matter (NOM) is better described by taking into account the dependence of the strength of binding on metal loading conditions. The utility of a linear differential equilibrium function for interpretation of metal ion binding data is demonstrated. This approach considers the binding intensity (log K*) as a function of metal ion loading (ı = bound metal/binding site concentration). Three methods for calculating this function are presented:– direct calculation from metal titration curves,– direct calculation from polarograms, and– compilation of data derived from interpretation of complexation in terms of one- or two- binding sites (e.g. Scatchard analysis), i.e. Cc (complexation capacity = effective site concentration)–K pairs.Heterogeneity also impacts on the apparent lability of complexes; complexes formed at the lowest metal loadings are the least labile.
Metal distribution and binding in balneological peats and their aqueous extracts by Peter Burba; André-Michael Beer; Julian Lukanov (pp. 419-425).
Binding of metals in typical bath peat samples (“Großes Gifhorner Moor”, Sassenburg/North Germany) and their aqueous extracts was characterized by means of a multi-method approach. For that purpose a sequential extraction procedure based on peat-filled chromatography columns was developed. Water-soluble metal and DOM (dissolved organic matter) fractions were subdivided by use of a stepwise increased pH gradient (pH 3.8–5), finally by the chelator EDTA and 0.1 mol L–1 hydrochloric acid. Metal fractions very strongly bound to peat were assessed by an aqua regia extraction.Metal determinations required were performed by atomic spectrometry methods (AAS, ICP–OES, and TXRF). The metal and DOM concentrations in the peat extracts varied significantly, depending on the natural variety of the peat matter under study (e.g., Al: 25–674, Cd: 0.05–0.2, Cu: 5– 15.4, Fe: 77–1785, Mn: 21–505, Ni: 2–33, Pb: < 1, Zn: 9– 715 (μg L–1); Na: 8–45, K: 1.3–14.9, Ca: 2–51, Mg: 1.1– 7.9 (mg L–1); 26–73 mg L–1 DOC). An increase of the pH increased the DOC (dissolved organic carbon) of the peat extracts, but hardly the concentration of heavy metals. The latter could only be re-mobilized by EDTA and dilute hydrochloric acid. Additional investigations of the peat extracts using tangential-flow ultrafiltration revealed that the heavy metals extracted at pH < 4 were predominantly dissociated. At higher pH (pH > 4.5) they were preferentially bound to macromolecular DOM. Moreover, using multistage ultrafiltration the size distribution of the DOM and their metal species was assessed.
Use of zwitterionic micelles in the eluent II: a new approach to ion chromatographic analysis of inorganic cations in biological fluids with direct sample injection by W. Hu; Hidenori Matsukami; Alexander Iles; Kiyoshi Hasebe; Shunan Cao; Kazuhiko Tanaka (pp. 426-428).
A new ion chromatographic (IC) technique has been developed for the determination of inorganic cations in biological fluids with direct sample injection. This involved the use of a mixed zwitterionic-micelle/electrolyte solution as an eluent. The proteins in the sample became bound to the zwitterionic micelles in the eluent and were thus eliminated from the column. The cations were separated by cation exchange. This method is ideal for the on-line, simultaneous determination of common inorganic cations (Na+, NH4 +, K+, Mg2+, and Ca2+) in urine and serum samples. Such an application was demonstrated experimentally. Non-suppressed conductivity was used for analyte detection. The detection limits obtained using this IC system were 2.94, 5.22, 34.9, 32.6, and 56.7 μg/L for Na+, NH4 +, K+, Mg2+, and Ca2+, respectively.
Determination of inorganic anions in human saliva by zwitterionic micellar capillary electrophoresis by Masanobu Mori; Wenzhi Hu; James S. Fritz; Hirohito Tsue; Takashi Kaneta; S. Tanaka (pp. 429-433).
Capillary electrophoresis (CE) using sulfobetaine-type zwitterionic micelles as the background electrolyte (BGE) has been used to determine inorganic anions in human saliva. The zwitterionic micelles resulted in unique migration behavior for the separation of inorganic anions. They also prevented adsorption of proteins on the inner wall of the capillary. These properties of the zwitterionic micelles enabled the direct determination of inorganic anions in human saliva. Three species of inorganic anions, NO2 –, NO3 –, and SCN–, were found in real samples and the analysis was achieved within 3 min. Direct UV-absorption was used as the detection method and the detection limits for these anions were 2.0, 1.0, and 5.0 μmol L–1, respectively (0.09, 0.06, and 0.30 μg mL–1).
Potentiometric stripping analysis (PSA) for monitoring of antimony in samples of vegetation from a mining area by M. C. Toro Gordillo; E. Pinilla Gil; M. A. Rodríguez González; A. Murciego Murciego; P. Ostapczuk (pp. 434-437).
A potentiometric stripping analysis (PSA) method has been developed and checked for the fast and reliable determination of antimony in vegetation samples of Cistus ladanifer from a mining area in Badajoz, Southwest Spain. The method, modified from previous PSA methods for Sb in environmental samples, is based on dry ashing of the homogenized leaves, dissolution in hydrochloric acid, and PSA analysis on a mercury film plated on to a glassy carbon disk electrode. The influence of experimental variables such as the deposition potential, the deposition time, the signal stability and the calibration parameters, has been investigated. The method has been compared with an independent technique (instrumental neutron activation analysis) by analysis of standards and reference materials and comparison of the results. As a result of automation of the PSA equipment, the proposed method enables unattended analysis of 20 digested samples in a total time of 2 h, thus providing a useful tool for Sb monitoring of a large number of samples.