Analytica Chimica Acta (v.615, #2)

Contents (iii).

Speciation information is vital for the understanding of the toxicity, mobility and bioavailability of elements in environmental or biological samples. Hyphenating high resolving power of separation techniques and element-selective detectors provides powerful tools for studying speciation of trace elements in environmental and biological systems. During the last five years several novel hybrid techniques based on capillary electrophoresis (CE) and atomic spectrometry have been developed for speciation analysis and metal–biomolecule interaction study in our laboratory. These techniques include CE on-line coupled with atomic fluorescence spectrometry (AFS), chip-CE on-line coupled with AFS, CE on-line coupled with flame heated quartz furnace atomic absorption spectrometry (FHF-AAS), and CE on-line coupled with electrothermal atomic absorption spectrometry (ETAAS). The necessity for the development of these techniques, their interface design, and applications in speciation analysis and metal–biomolecule interaction study are reviewed. The advantages and limitations of the developed hybrid techniques are critically discussed, and further development is also prospected.
Keywords: Review; Capillary electrophoresis; Atomic spectrometry; Hybrid technique; Speciation analysis; Interaction;

A high-pressure microwave digestion was applied for microwave-assisted extraction (MAE) of mercury species from sediments and zoobenthos samples. A mixture containing 3 mol L−1 HCl, 50% aqueous methanol and 0.2 mol L−1 citric acid (for masking co-extracted Fe3+) was selected as the most suitable extraction agent. The efficiency of proposed extraction method was better than 95% with R.S.D. below 6%. A preconcentration method utilizing a “homemade” C18 solid phase extraction (SPE) microcolumns was developed to enhance sensitivity of the mercury species determination using on-column complex formation of mercury-2-mercaptophenol complexes. Methanol was chosen for counter-current elution of the retained mercury complexes achieving a preconcentration factor as much as 1000. The preconcentration method was applied for the speciation analysis of mercury in river water samples. The high-performance liquid chromatography-cold vapour atomic fluorescence spectrometric (HPLC/CV-AFS) method was used for the speciation analysis of mercury. The complete separation of four mercury species was achieved by an isocratic elution of aqueous methanol (65%/35%) on a Zorbax SB-C18 column (4.6 mm × 150 mm, 5 μm) using the same complexation reagent (2-mercaptophenol). The limits of detection were 4.3 μg L−1 for methylmercury (MeHg+), 1.4 μg L−1 for ethylmercury (EtHg+), 0.8 μg L−1 for inorganic mercury (Hg2+), 0.8 μg L−1 for phenylmercury (PhHg+).
Keywords: Mercury; Speciation; Aquatic ecosystem; High-performance liquid chromatography-cold vapour atomic fluorescence spectrometry; Preconcentration;

The electrospray ionization ion trap multiple-stage tandem mass spectrometry (ESI-MS n ) and electrospray ionization Fourier transform ion cyclotron resonance multiple-stage tandem mass spectrometry (ESI-FT-ICR-MS n ) have been applied successfully to the direct investigation of a number of dibenzocyclooctadiene lignan constituents from the methanol extracts of the Fructus Schisandrae in the positive ion mode. The detailed structural characterization of the same skeleton and different peripheral substituents had been studied and the precise elemental compositions of ions at high mass resolution had been obtained. So the fragmentation mechanisms could be clarified. And the lignan components in Schisandra chinensis (Turcz.) Baill. fruits (SCF) and Schisandra sphenanthera Rehd. et Wils. fruits (SSF) were identified by comparing the structural information and fragmentation mechanisms. Then a pair of isobaric compounds was differentiated. Meanwhile these two similar fruits were distinguished. The research results demonstrated that ESI-MS n technique is a sensitive, selective and effective tool for the direct analysis and rapid determination of constituents in complex mixtures from nature products. And these should be useful for the identification of similar compounds and differentiation of similar species from Chinese herbs.
Keywords: Lignans; Schisandra chinensis; Schisandra sphenanthera; Structural information; Electrospray ionization ion trap multiple-stage tandem mass spectrometry; Electrospray ionization Fourier transform ion cyclotron resonance multiple-stage tandem mass spectrometry;

Structure generation and mass spectral classifiers have been incorporated into a new method to gain further information from low-resolution GC–MS spectra and subsequently assist in the identification of toxic compounds isolated using effect-directed fractionation. The method has been developed for the case where little analytical information other than the mass spectrum is available, common, for example, in effect-directed analysis (EDA), where further interpretation of the mass spectra is necessary to gain additional information about unknown peaks in the chromatogram. Structure generation from a molecular formula alone rapidly leads to enormous numbers of structures; hence reduction of these numbers is necessary to focus identification or confirmation efforts. The mass spectral classifiers and structure generation procedure in the program MOLGEN-MS was enhanced by including additional classifier information available from the NIST05 database and incorporation of post-generation ‘filtering criteria’. The presented method can reduce the number of possible structures matching a spectrum by several orders of magnitude, creating much more manageable data sets and increasing the chance of identification. Examples are presented to show how the method can be used to provide ‘lines of evidence’ for the identity of an unknown compound. This method is an alternative to library search of mass spectra and is especially valuable for unknowns where no clear library match is available.
Keywords: Effect-directed analysis; Structure generation; Mass spectral classifiers; Confirmation; MODELKEY;

A theoretical approach for designing fluorescent reagentless biosensors: The optical model by Javier Galbán; Arantzazu Delgado-Camón; Vanesa Sanz; Isabel Sanz-Vicente; Susana de Marcos (148-157).
In this paper a mathematical model describing the analytical signal obtained in fluorescence sensors is presented and compared with other commonly used models. The model starts from the Kubelka–Munk theory for solid surfaces but incorporates new theoretical improvements, being principally: (a) the increase in the effective optical pathlength due to the Scattering Induced Path Variation (SIPV), the incorporation of this parameter allows us to deduce that the fluorescence intensity from solid surfaces does not linearly change with the fluorophore concentrations; (b) the influence of the inner filter effect and how the error can be rectified and (c) the calculation of the scattering coefficients in sensor films for this kind of sensor. From this model it is possible to predict the effect of the fluorophore concentration, the sensor film scattering coefficient and the sample inner filter effect on the fluorescence signal. The conclusions obtained can be extended to other types of fluorescence measurements from solid surfaces.
Keywords: Theoretical model; Reagentless biosensors; Solid surface fluorescence;

A reagentless amperometric immunosensor for α-1-fetoprotein based on gold nanowires and ZnO nanorods modified electrode by Xuxiao Lu; Huiping Bai; Ping He; Yongying Cha; Guangming Yang; Lin Tan; Yunhui Yang (158-164).
A novel strategy for the preparation of reagentless immunosensor for rapid determination of α-1-fetoprotein (AFP) in human serum has been developed. The immunosensor was prepared by immobilizing α-1-fetoprotein antibody (AFP Ab) onto the glassy carbon electrode modified by gold nanowires (Au NWs) and ZnO nanorods (ZnO NRs) composite film. Gold nanowires and ZnO nanorods were produced by an electrodeposition strategy using nanopore polycarbonate (PC) membrane. A sandwich immunoassay format was employed to detect AFP with horseradish peroxidase (HRP)-labeled AFP as tracer. The morphology of the Au NWs and ZnO NRs composite film has been investigated by scanning electron microscopy (SEM) and energy disperse spectroscopy (EDS) analysis. The resulting immunosensor offered an excellent amperometric response for AFP ranging from 0.5 to 160.0 ng mL−1 with a detection limit of 0.1 ng mL−1. Because of the combination of the biocompatibility of ZnO NRs and the direct electron-transfer of Au NWs between HRP and electrode, the proposed immunosensor displayed a direct electrochemical response of HRP to the reduction of H2O2 with high sensitivity, quick response, good repeatability and long-term stability.
Keywords: α-1-Fetoprotein; Amperometric immunosensor; Gold nanowire; ZnO nanorods;

In this study, the fundamental aspects of gas chromatography with a pulsed flame photometric detector were investigated through the calibration of gaseous reduced sulfur compounds based on the direct injection method. Gaseous standards of five reduced sulfur compounds (hydrogen sulfide, methane thiol, dimethyl sulfide, carbon disulfide, and dimethyl disulfide) were calibrated as a function of injection volume and concentration level. The results were evaluated by means of two contrasting calibration approaches: fixed standard concentration method (variable volumetric injection of standard gases prepared at a given concentration) and fixed standard volume method (injection of multiple standards with varying concentrations at a given volume). The optimum detection limit values of reduced sulfur compounds, when estimated at 100 μL of injection volume, ranged from 2.37 pg (carbon disulfide) to 4.89 pg (dimethyl sulfide). Although these detection limit values improved gradually with decreasing injection volume, the minimum detectable concentration (e.g., in nmol mol−1 scale) remained constant due to a balance by the sample volume reduction. The linearity property of pulsed flame photometric detector also appeared to vary dynamically with changes in its sensitivity. According to this study, the performance of pulsed flame photometric detector, when tested by direct injection method, is highly reliable to precisely describe the behavior of reduced sulfur compounds above ∼20 nmol mol−1.
Keywords: Reduced sulfur compounds; Calibration; Pulsed flame photometric detection; Direct injection;

A general and broad class-specific enzyme-linked immunosorbent assay was developed for the O,O-dimethyl organophosphorus pesticides, including malathion, dimethoate, phenthoate, phosmet, methidathion, fenitrothion, methyl parathion and fenthion. Three haptens with different spacer-arms were synthesized. The haptens were conjugated to bovine serum albumin (BSA) for immunogens and to ovalbumin (OVA) for coating antigens. Rabbits were immunized with the immunogens and six polyclonal antisera were produced and screened against each of the coating antigens using competitive indirect enzyme-linked immunosorbent assay for selecting the proper antiserum. The effect of hapten heterology on immunoassay sensitivity was also studied. The antibody–antigen combination with the most selectivity for malathion was further optimized and tested for tolerance to co-solvent, pH and ionic strength changes. The IC50 values, under optimum conditions, were estimated to be 30.1 μg L−1for malathion, 28.9 μg L−1 for dimethoate, 88.3 μg L−1 for phenthoate, 159.7 μg L−1 for phosmet, 191.7 μg L−1 for methidathion, 324.0 μg L−1 for fenitrothion, 483.9 μg L−1 for methyl parathion, and 788.9 μg L−1 for fenthion. Recoveries of malathion, dimethoate, phenthoate, phosmet and methidathion from fortified Chinese cabbage samples ranged between 77.1% and 104.7%. This assay can be used in monitoring studies for the multi-residue determination of O,O-dimethyl organophosphorus pesticides.
Keywords: Organophosphorus pesticide; Class-specific immunoassay; Hapten synthesis; Heterology; Enzyme-linked immunosorbent assay;

Salicylate-spectrophotometric determination of inorganic monochloramine by Hui Tao; Zhong-Lin Chen; Xing Li; Yan-Ling Yang; Gui-Bai Li (184-190).
On the basis of classical Berthelot reaction, a simple salicylate-spectrophotometric method was developed for quantitative determination of inorganic monochloramine in water samples. With the catalysis of disodium pentacyanonitrosylferrate(III), inorganic monochloramine reacts with salicylate in equimolar to produce indophenol compound which has an intense absorption at 703 nm. Parameters that influence method performance, such as pH, dosage of salicylate and nitroprussiate and reaction time, were modified to enhance the method performance. By using this method, inorganic monochloramine can be distinguished from organic chloramines and other inorganic chlorine species, such as free chlorine, dichloramine, and trichloramine. The molar absorptivities of the final products formed by these compounds are below ±3% of inorganic monochloramine, because of the α-N in them have only one exchangeable hydrogen atom, and cannot react with salicylate to produce the indophenol compound. The upper concentrations of typical ions that do not interfere with the inorganic monochloramine determination are also tested to be much higher than that mostly encountered in actual water treatment. Case study demonstrates that the results obtained from this method are lower than DPD-titrimetric method because the organic chloramines formed by chlorination of organic nitrogenous compounds give no response in the newly established method. And the result measured by salicylate-spectrophotometric method is coincident with theoretical calculation.
Keywords: Monochloramine; Organic chloramines; Berthelot reaction; Organic nitrogenous compound; Determination;