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Analytica Chimica Acta (v.603, #1)

Contents (pp. v-vi).

Editorial Board (pp. co1).

A fully automated system for inorganic antimony preconcentration and speciation in urine by Pablo H. Pacheco; Raúl A. Gil; Luis D. Martinez; Griselda Polla; Patricia Smichowski (pp. 1-7).

A study was undertaken to ascertain the analytical capabilities ofl-methionine immobilized on controlled pore glass for Sb preconcentration and speciation. A fully automated on-line system, implemented with hydride generation (HG) and inductively coupled plasma optical emission spectrometry (ICP OES), was used. Sb(III), at pH 10 was selectively retained in the column containing the immobilized aminoacid, while Sb(V) was not retained at all. A 30% HCl solution was used as eluent agent. Prior to total Sb determination, a pre-reduction step with thiourea was necessary. An on-line pH adjusting and pre-reduction of Sb(V) was achieved in a fully automated system. The detection limit for the preconcentration of 10mL of an aqueous solution was 70ngL⁻¹ with a relative standard deviation of 2%. An enrichment factor of 20 was achieved when 10mL of sample was passed through the system, reaching a throughput of 23 samples per hour. The method was successfully applied to the determination of Sb(III) and total Sb in urine.

Keywords: l; -Methionine; Antimony; Speciation analysis; Urine

Multivariate calibration on NIR data: Development of a model for the rapid evaluation of ethanol content in bakery products by Alessandra Bello; Federica Bianchi; Maria Careri; Marco Giannetto; Giovanni Mori; Marilena Musci (pp. 8-12).

A new NIR method based on multivariate calibration for determination of ethanol in industrially packed wholemeal bread was developed and validated. GC-FID was used as reference method for the determination of actual ethanol concentration of different samples of wholemeal bread with proper content of added ethanol, ranging from 0 to 3.5% (w/w) . Stepwise discriminant analysis was carried out on the NIR dataset, in order to reduce the number of original variables by selecting those that were able to discriminate between the samples of different ethanol concentrations. With the so selected variables a multivariate calibration model was then obtained by multiple linear regression. The prediction power of the linear model was optimized by a new “leave one out” method, so that the number of original variables resulted further reduced.

Keywords: Near InfraRed; Multivariate analysis; Ethanol; Bread

Mean centering of ratio spectra as a new method for determination of rate constants of consecutive reactions by Morteza Bahram (pp. 13-19).

Mean centering of ratio spectra is applied to resolve two-way kinetic-spectral data and acquire the rate constants and the spectrum of intermediate component. The proposed method can be applied for two-step consecutive reactions. The method is based on the mean centering of ratio spectra in order to obtain kinetic profile of intermediate component. Rate constants can be obtained using computational fitting. Given the kinetic parameters, the absorption spectrum of intermediate can be obtained through least squares regression. The proposed method can be applied to the reaction systems that reactant, intermediate or final product does not absorb in the investigation wavelength region. Also for very slow one-step reactions that pure spectrum for product is not available or overlaps completely with reactant spectrum, the proposed method can be used to resolve kinetic profile and consequently the pure spectrum of product. The applicability of the method has been evaluated by using model data. Alkaline hydrolysis of dimethyl phthalate as a real system was also studied by the proposed method.

Keywords: Mean centering; Ratio spectra; Rate constants determination; Consecutive reactions

3-Way characterization of soils by Procrustes rotation, matrix-augmented principal components analysis and parallel factor analysis by J.M. Andrade; M. Kubista; A. Carlosena; D. Prada (pp. 20-29).

Three different approaches for 3-way analyses, namely, Procrustes rotation, parallel factor analysis (PARAFAC) and matrix-augmented principal component analysis, have been compared considering a four-seasons study on soil pollution. Each sampling season comprised 92 roadsoil samples and 12 analytical variables (heavy metals, loss on ignition, pH and humidity). Results show that the three chemometric techniques lead to essentially the same conclusions. Hence, Procrustes rotation, a mathematical technique scarcely applied in analytical chemistry, revealed as a useful tool for 3-way data analysis with potential advantages, including its conceptual simplicity and straightforward interpretation of the results. A novel application of the consensus vectors allowed definition of “consensus scores” so that visualization of the samples and temporal patterns can be made. Results also suggested that the trilinearity assumption imbedded in PARAFAC is essentially fulfilled when studying the temporal evolution of an environmental system where no new pollution sources appear during the course of the study.

Keywords: Soil; Heavy metals; Procrustes rotation; Matrix-augmented principal component analysis; Parallel factor analysis

Determination of trace sulfite by direct and indirect methods using differential pulse polarography by Ümmihan T. Yilmaz; Güler Somer (pp. 30-35).

Sulfite determination plays an important role since it is used in some food stuff as protecting agent. The objective of this study was to develop a new and simple method for the determination of sulfite so that it can be used in routine food analysis. A differential pulse polarographic (DPP) method has been used for this purpose since the results obtained with this method are very reproducible and the instrument used is not expensive. Various acids and pH values have been studied such as 4M, 1.0M, 0.1M HCl and HClO₄, and HAc-NaAc electrolyte. The best medium was pH 3–5 acetate medium, where the reduction peak of sulfite at about −0.6V was used. At lower pH values sulfite was escaping as SO₂ while nitrogen gas was passing. At higher pH values, on the other hand, the peak was too small for the accurate determination.Interference of most common elements such as Fe, Cu, Pb and Cd was investigated and it was found that only Cd had an overlapping peak. This interaction could be eliminated using EDTA. The detection limit found was 2×10⁻⁶M in acetate buffer. An indirect method was developed also where the reaction between selenite and sulfite has been used. In this method a known amount of selenite was added and the selenite after reaction has been determined. The detection limit (7×10⁻⁷M) was lower than direct method.The quantity of sulfite present in dried apricots was found between 1.5 and 1.7gkg⁻¹ of dried fruit.

Keywords: Sulfite; Determination; Reduction; Differential pulse polarography; Apricots

Pressurized liquid extraction-assisted mussel cytosol preparation for the determination of metals bound to metallothionein-like proteins by Sandra Santiago-Rivas; Antonio Moreda-Piñeiro; Pilar Bermejo-Barrera; Jorge Moreda-Piñeiro; Elia Alonso-Rodríguez; Soledad Muniategui-Lorenzo; Purificación López-Mahía; Darío Prada-Rodríguez (pp. 36-43).

The possibilities of pressurized liquid extraction (PLE) have been novelty tested to assist the cytosol preparation from wet mussel soft tissue before the determination of metals bound to metallothionein-like proteins (MLPs). Results obtained after PLE were compared with those obtained after a classical blending procedure for mussel cytosolic preparation. Isoforms MLP-1 (retention time of 4.1min) and MLP-2 (retention time of 7.4min) were separated by anion exchange high-performance liquid chromatography (HPLC) and the concentrations of Ba, Cu, Mn, Sr and Zn bound to MLP isoforms were directly measured by inductively coupled plasma-atomic emission spectrometry (ICP-OES) as a multi-element detector. The optimized PLE-assisted mussel cytosol preparation has consisted of one extraction cycle at room temperature and 1500psi for 2min. Since separation between the solid mussel residue and the extract (cytosol) is performed by the PLE system, the cytosol preparation method is faster than conventional cytosol preparation methods by cutting/blending using Ultraturrax or Stomacher devices.

Keywords: Pressurized liquid extraction; Metallothionein-like proteins; Multi-element determination; Mussels; High-performance liquid chromatography; Inductively coupled plasma-optical emission spectrometry

A new approach for simultaneous determination of Co(II), Ni(II), Cu(II) and Pd(II) using 2-thiophenaldehyde-3-thiosemicarbazone as reagent by solid phase microextraction–high performance liquid chromatography by Varinder Kaur; Jatinder Singh Aulakh; Ashok Kumar Malik (pp. 44-50).

A new method is proposed herein for the sorption, separation and simultaneous determination of Co(II), Ni(II), Cu(II) and Pd(II) using 2-thiophenaldehyde-3-thiosemicarbazone (TPTS) as a reagent by solid phase microextraction–high performance liquid chromatography–UV detection. The method is based upon the sorption of metal complexes on polydimethylsiloxane (PDMS) fiber from aqueous solution followed by desorption in the desorption chamber of solid phase microextraction–high performance liquid chromatography (SPME–HPLC) interface. Reversed phase high performance liquid chromatography using acetonitrile:water (65:35) as an eluent on a C18 column has been used to achieve the separation. The effects of agitation, addition of salts, extraction time and desorption time are examined to obtain optimized conditions. The detection limits for Co(II), Ni(II), Cu(II) and Pd(II) are 9, 6, 1 and 7ngL⁻¹ based on 3 σ of blank response. The precision is calculated to be less than 3.5% (R.S.D.) for all species. A 10 time enhancement in the signal is observed for SPME when compared with direct analysis. The method is successfully applied to several synthetic mixtures without interference from other common metal ions such as Mo(VI), V(V), Ag(I), Sn(IV), Cd(II), Zn(II), Pb(II), Cr(III) and Cr(VI). The proposed method is tested for the determination of Co(II), Ni(II), Cu(II) and Pd(II) in alloys and water samples spiked with these metal ions.

Keywords: Solid phase microextraction; High performance liquid chromatography; 2-Thiophenaldehyde-3-thosemicarbazone; Cobalt; Nickel; Copper; Palladium

Determination of bisphenols A and F and their diglycidyl ethers in wastewater and river water by coacervative extraction and liquid chromatography–fluorimetry by Ana Ballesteros-Gómez; Francisco-Javier Ruiz; Soledad Rubio; Dolores Pérez-Bendito (pp. 51-59).

A simple, rapid and sensitive analytical method was developed for the simultaneous determination of bisphenol A (BPA), bisphenol F (BPF) and their corresponding diglycidyl ethers (BADGE and BFDGE) in wastewater and river water, in order to have a useful tool for evaluating their fate and distribution in aquatic environments. It was based on their extraction with coacervates made up of decanoic acid reverse micelles and subsequent determination by liquid chromatography–fluorimetry. The procedure involved the extraction of 10.8mL of water sample for 5min, its centrifugation for 10min to accelerate phase separation and then the chromatographic analysis of the target compounds. Clean-up or solvent evaporation steps were not necessary to get the required sensitivity and selectivity. Extraction efficiencies and concentration factors mainly depended on the amount of decanoic acid and tetrahydrofuran making up the coacervate. A general equation for the prediction of the volume of the coacervate as a function of its components has been proposed and fitted by nonlinear regression. This equation permits to know a priori the maximum concentration factors that can be achieved under given experimental conditions. Extractions were independent of salt addition (up to 1M), the temperature (up to 60°C) and the pH (below 4) rendering the method robust. Recoveries in samples ranged between about 80 and 92% and the actual concentrations factors were between 87 and 102, which resulted in practical detection limits around 30–35ngL⁻¹. The method was successfully applied to the determination of the target pollutants in raw and treated sewage from four mechanical-biological treatment plants and three rivers. Bisphenols and their diglycidyl ethers were present in wastewater influents at concentrations in the range 0.96 to 1.6μgL⁻¹. The biological treatment at the wastewater treatment plants (WWTP_s) studied reduced the concentration of BPA and BPF in a percentage above 75%, while diglycidyl ethers were not detected in most of the effluents investigated. Only BPA was detected in surface waters.

Keywords: Coacervation; Reverse micelles; Bisphenols; Environmental water; River; Wastewater; Liquid–liquid extraction; Liquid chromatography; Fluorimetry

Micro-gas analysis system for measurement of nitric oxide and nitrogen dioxide: Respiratory treatment and environmental mobile monitoring by Kei Toda; Yuki Hato; Shin-Ichi Ohira; Takao Namihira (pp. 60-66).

In this paper, novel microsystems for gas analysis and gas generation are described. The same microchannel devices covered with a gas permeable membrane were used for both the gas collection and the gas generation. For the first time, a dual liquid flow system was utilized in a micro-gas analysis system. Even though micropumps are utilized in the dual line microsystem, a good baseline was obtained in the NO₂ measurement with Griess–Saltzman chemistry. The system was developed for on-site measurements in medical treatment; the treatment is of respiratory disease syndrome by NO inhalation and the monitoring is of the product NO and the harmful byproduct NO₂. The system was also applied to mobile atmospheric monitoring. Chemical NO generation using the microchannel device was investigated for safe NO inhalation as an alternative to a NO generator based on pulsed arc discharge.

Keywords: Micro-gas analysis system; Nitric oxide; Nitrogen dioxide; Respiratory treatment; Atmospheric mobile monitoring

Application of solid-phase extraction coupled with freezing-lipid filtration clean-up for the determination of endocrine-disrupting phenols in fish by Yun Gyong Ahn; Jeoung Hwa Shin; Hye-Young Kim; Jeehyeong Khim; Mi-Kyoung Lee; Jongki Hong (pp. 67-75).

An analytical method has been developed for the determination of endocrine-disrupting phenols (eight alkylphenols and bisphenol A) in fish samples. The extraction of nine phenols from fish samples was carried out by ultrasonification. After the extraction, high levels of lipids were removed by freezing-lipid filtration instead of the traditional methods of column chromatography or saponification. During freezing-lipid filtration, about 90% of the lipids were eliminated without any significant loss of phenolic compounds. For further purification, hydrophilic–lipophilic balanced copolymer (HLB) sorbent with a poly(divinylbenzene-co- N-vinylpyrrolidone) phase and Florisil-solid-phase extraction (SPE) cartridges were used to eliminate the remaining interferences. Silyl-derivatization, with N, N′-methyl-( tert-butyldimethylsilyl) trifluoroacetamide (MTBSTFA), was applied to enhance the sensitivity of detection of phenolic compounds. Quantification was performed by gas chromatography/mass spectrometry (GC/MS)-selected ion monitoring (SIM) mode, using deuterium-labeled internal standards. Spiking experiments were carried out to determine the recovery, precision and detection limit of the method. The overall recoveries ranged between 70 and 120%, with relative standard deviations of 3–17% for the entire procedure. The detection limits of the method for the nine phenols ranged from 0.02 to 0.41ngg⁻¹. The method provided simultaneous screening and accurate confirmation of each phenol when applied to biological samples.

Keywords: Endocrine-disrupting phenols; Fish; Freezing-lipid filtration; Solid-phase extraction; Silyl-derivatization; Gas chromatography/mass spectrometry

Single probe nucleic acid immobilization on chemically modified single protein by controlling ionic strength and pH by Ryujiroh Yamasaki; Masateru Ito; BongKuk Lee; HoSup Jung; HeaYeon Lee; Tomoji Kawai (pp. 76-81).

In an effort toward determining the feasibility of single molecule analysis, we describe a case whereby the binding of one biotinylated DNA to one streptavidin molecule via electrostatic interactions was controlled by altering in pH 4.0–9.0 and 0.16 of the ion strength. The quantitative analysis of immobilized probe ssDNA was realized in real-time via a quartz crystal microbalance (QCM) and electrochemical (EC) measurement in the range 100pM to 50μM of probe oligonucleotide concentration. The variation amount of biotinylated ssDNA immobilized on the streptavidin-modified surface at pH 7.5 was about 0.16pmol, giving a ratio of streptavidin to biotinylated ssDNA of about 1:1.1. On the other hand, at pH 4.9, it was immobilized about 0.29pmol. From the shape of the Langmuir plot and QCM, the immobilization efficiency of biotinylated DNA via streptavidin at pH 4.9 was approximately twofold that at pH 7.5. In view points of the reaction velocity, it was increased with decreasing buffer solution pH, indicating a strong interaction of negatively charged probe DNA with the positively charged streptavidin. And also the EC response value of Δ I/ I_streptavidin for the immobilized biotinylated ssDNA in pH 4.9 was about 49%, while the corresponding value for the pH 7.5 was approximately 34%. As DNA molecules possess negative charges, electrostatic repulsion occurred between streptavidin and biotinylated ssDNA at pH 7.5. At pH 4.9, the attraction between the biotinylated ssDNA and streptavidin resulted in increased adsorption which has an isoelectric point of about 5.9. It was deduced that the binding of biotinylated ssDNA to one or two of the four binding sites of streptavidin can be controlled by adjusting the pH-controlled electrostatic interaction.

Keywords: Streptavidin monolayer; Streptavidin–biotin interaction; Quantitative analysis; Binding rate; pH and ionic strength dependence

Design of an optimal allele-specific oligonucleotide probe for the efficient discrimination of a thermodynamically stable (G·T) mismatch by Fausto Lucarelli; Giovanna Marrazza; Marco Mascini (pp. 82-86).

A general approach that allows reliable detection of a single base-pair mismatch is presented. Specifically, how important a careful design of the allele-specific oligonucleotide (ASO) probe is, was demonstrated for a G·T mispair highly stable from the thermodynamic point of view. This study involved comparison of six ASO probes of variable length (25 to 9-mer), with a similar GC composition and designed to hybridise the target in a way that the mutation centrally occurred with respect to the duplex region.All hybridisation experiments were performed on the surface of probe-modified screen-printed gold electrodes. Transduction of the interfacial biorecognition events was then accomplished by means of electrochemical measurements, using a streptavidin-conjugated alkaline phosphatase label and a suitable substrate.While the longest ASO probes (25 and 15-mer) did not allow significant differentiation of the mutant from the wild-type sequence and the shortest probe (9-mer) was incapable of forming a stable hybrid in the given hybridisation conditions, increasing levels of selectivity were observed employing the 13, 12 and 11-mer probes, respectively. In particular, the 11-mer ASO probe allowed resolving matched and mismatched duplexes with relative selectivity as high as 50:1 even operating in non-stringent hybridisation conditions, using buffers with a relatively high ionic strength, at room temperature and without the need for including chemicals such as formamide into the hybridisation medium.The results shown in this paper may serve to further improve the reliability of the hybridisation-based mutation analysis.

Keywords: Allele-specific oligonucleotide; Mismatch; Hybridisation stringency; Electrochemical genosensor; Enzyme label

Synthesis of Zn(II) ion-imprinted solid-phase extraction material and its analytical application by Jingchan Zhao; Bing Han; Yanfeng Zhang; Dandan Wang (pp. 87-92).

Zn(II) ion-imprinted polymer materials used for solid-phase extraction (SPE) column were prepared by the copolymerization of 8-acryloyloxyquinoline (8-AOQ) monomer and a crosslinker ethylene glycol dimethacrylate (EGDMA) in the presence of 2,2′-azobisisobutyronitrile (AIBN) as an initiator. After removing Zn(II) ion from the polymer, molecularly imprinted polymers (MIPs) capable of selectively rebinding Zn(II) ion were obtained. The maximum adsorption capacity of Zn(II) on MIPs beads was about 3.9mgg⁻¹. The effect of pH and flow rate for quantitative enrichment was also investigated. The Zn(II)-imprinted microbeads have a greater affinity for Zn(II) with respect to Cu(II), Co(II) and Ni(II) ions. A detection limit of 0.65μgL⁻¹(3 σ) and a relative standard deviation (R.S.D., n=7) of 2.9% were obtained. The MIPs–SPE preconcentration procedure showed a linear calibration curve within concentration range from 0.65 to 130μgL⁻¹. Zn(II) ion-imprinted beads enabled the selective extraction of zinc ions from a complex matrix, and after 20 times of adsorption and desorption cycle, the recovery of adsorption capacity of Zn(II) on MIPs beads was only decreased 3.2%. The results suggested that these MIPs can be used several times without considerable loss of adsorption capacity.

Keywords: Zinc ion; Molecularly imprinted polymer; Solid-phase extraction; Ionic imprinting

Modeling transport effects of perfluorinated and hydrocarbon surfactants in groundwater by using micellar liquid chromatography by Rashad N. Simmons; Victoria L. McGuffin (pp. 93-100).

The effects of hydrocarbon and perfluorinated surfactants, above their critical micelle concentration (CMC), on the transport of neutral environmental pollutants are compared. Reversed-phase micellar liquid chromatography is used to model the groundwater system. The octadecylsilica stationary phase serves to simulate soil particles containing organic matter, whereas the aqueous surfactant mobile phases serve to simulate groundwater containing a surfactant at varying concentrations. Sodium dodecyl sulfate and lithium perfluorooctane sulfonate are used as representatives of the hydrocarbon and perfluorinated surfactants, respectively. Benzene, mono- and perhalogenated benzenes, and polycyclic aromatic hydrocarbons are used as models for environmental pollutants.Transport effects were elucidated from the retention factor, k, and the equilibrium constant per micelle, K_eq, of the model pollutants in the individual surfactants. Based on k values, the transport of the model pollutants increased in both surfactant solutions in comparison to pure water. As the concentration of the surfactants increased, the transport of the pollutants increased as well. Notably, the K_eq values of the pollutants in the perfluorinated surfactant were at least an order of magnitude less than those in the hydrocarbon surfactant. Overall, these results suggest that the presence of a perfluorinated surfactant, above its CMC, increases the transport of pollutants in a groundwater system. However, the perfluorinated surfactant exhibits a lesser transport effect than the hydrocarbon surfactant.

Keywords: Perfluorinated surfactant; Hydrocarbon surfactant; Environmental transport; Micellar liquid chromatography; Aromatic hydrocarbons

Study of the interactions between fluoroquinolones and human serum albumin by affinity capillary electrophoresis and fluorescence method by Li-Wei Zhang; Kun Wang; Xin-Xiang Zhang (pp. 101-110).

The interactions between fluoroquinolones and human serum albumin (HSA) were investigated by affinity capillary electrophoresis (ACE) and fluorescence quenching technique. Based on the efficient separation of several fluoroquinolones using a simple phosphate buffer, the binding constants of fluoroquinolones with HSA were determined simultaneously during one set of electrophoresis by ACE method. The thermodynamic parameters were obtained from data at different temperatures, and the negative Δ H and Δ S values showed that both hydrogen bonds and van der Waals interaction played major roles in the binding of fluoroquinolones to HSA. The interactions were also studied by fluorescence quenching technique. The results of fluorescence titration revealed that fluoroquinolones had the strong ability to quenching the intrinsic fluorescence of HSA through the static quenching procedure. The binding site number n, apparent binding constant K_b and the Stern–Volmer quenching constant K_sv were determined. The thermodynamic parameters were also studied by fluorescence method, and the results were consonant with that of ACE.

Keywords: Affinity capillary electrophoresis; Separation; Fluorescence method; Binding constant; Fluoroquinolones; Human serum albumin

A highly specific immunoassay for microcystin-LR detection based on a monoclonal antibody by Jian-Wu Sheng; Miao He; Han-Chang Shi (pp. 111-118).

Microcystins (MC) are cyanobacterial hepatotoxins responsible for animal-poisoning and human health incidents. Immunoassays provide a sensitive and fast means to detect these toxins, but cross-reactivity (CR) characteristic of different antibodies was variable. Here, we have produced and characterized a monoclonal antibody (Clone MC8C10) with highly specificity against the most frequent and most toxic variant of microcystins, MC-LR. MC8C10 is more specific against MC-LR among the reported antibodies before. The immunogen was synthesized from the modified MC-LR and bovine serum albumin (BSA). An indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) with MC8C10 was established to detect the MCs in waters, which showed highly specificity with MC-LR, and have a detection limit for MC-LR 0.1μgL⁻¹, the 50% inhibition concentration (IC₅₀) for MC-LR was 1.8±0.1μgL⁻¹ and the quantitative detection range was from 0.3 to 10μgL⁻¹. The [4-arginine] microcystins and the nodularin-R showed lower cross-reactivates (CR<10%), and other MCs such as MC-LF and MC-LW are not recognized (CR<10⁻⁴). The analysis results of real water samples with ic-ELISA showed that all the coefficients of variation were less than 15%, and the recovery was (100.3±5.9)%. So the highly specific ic-ELISA will commendably suit for sensitive analysis for MC-LR in surface water as well as drinking water.

Keywords: Microcystin-LR; Monoclonal antibody MC8C10; Enzyme-linked immunosorbent assay (ELISA); high specificity

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Analytica Chimica Acta (v.603, #1)