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Analytica Chimica Acta (v.625, #2)

Editorial Board (pp. i).

Contents (pp. iii-iv).

Simultaneous determination of major to ultratrace elements in geological samples by fusion-dissolution and inductively coupled plasma mass spectrometry techniques by S. García de Madinabeitia; M.E. Sánchez Lorda; J.I. Gil Ibarguchi (pp. 117-130).

A method has been developed for the simultaneous quantification of major to ultratrace elements in geological samples using quadrupole ICP-MS techniques. The sample preparation involves fusion with LiBO₂ and dilution in HNO₃-HF which allows complete decomposition of refractory minerals and quantification of the elements of interest. The effects of high Total Dissolved Solids (TDS) and Li in the solution are minimized using a matrix-tolerant interface and conditioning the instrument with LiBO₂ solution. The signal drift is moreover controlled using conventional internal standards and specific Drift Correction Standards (DCS). A key issue of the technique is the external calibration using selected Certified Reference Materials (CRM). Depending on the sample type and analytes of interest three optimized programmable modes are used sequentially: Standard, Collision Cell (CCT) and Kinetic Energy Discrimination (KED) mode. The method allows to quantify more than 40 elements in concentrations from tens-of-percent to <0.1ppm levels during a single experiment. The method has been validated through the analysis of different CRMs with recovery factors of ca. 100% and typical 2 σ errors of <10%.

Keywords: Inductively coupled plasma mass spectrometry; Major; Trace; Ultratrace; Fusion; Geochemical analysis

On-line redox speciation analysis of antimony usingl-proline immobilized on controlled pore glass and hydride generation inductively coupled plasma optical emission spectrometry for detection by Amauri A. Menegário; Patricia Smichowski; Paulo S. Tonello; Griselda Polla; Eliane P. Oliveira; Ricardo E. Santelli (pp. 131-136).

l-proline was immobilized on controlled pore glass to study the ability of this material for the separation and preconcentration of Sb(III) and Sb(V). The substrate was packed in a minicolumn and incorporated in a flow injection system. The effluents of the on-line solid phase extraction (before and after elution) were directly coupled to the hydride generation inductively coupled plasma optical emission spectrometry system. The effect of pH, sample (and eluent) volume, flow rates of sample loading and elution on separation of Sb(III) e Sb(V) were evaluated. Our experiments demonstrated that Sb(V) was not retained and it was selectively determined during the loading step, while retained Sb(III) was determined after elution. The proposed system was also used for the selective preconcentration of Sb(III). In this case, a preconcentration factor of 11 and a limit of detection of 90ngL⁻¹ for Sb(III) were achieved when 8mL of sample were loaded into the column. The speciation analysis of inorganic Sb in river water and effluent samples was performed using the proposed method. The values obtained for total Sb (obtained by sum of Sb(III) and Sb(V)) were in good agreement with expected values. Recoveries of Sb(III) and Sb(V) in the river water Standard Reference Material 1640 (from National Institute of Standard and Technology) and spiked river waters were between 83 and 111%.

Keywords: Antimony; l; -proline; Speciation analysis; Controlled pore glass; Hydride generation

Covalent binding of sensor phases - a recipe for stable potentials of solid-state ion-selective sensors by Ewa Grygołowicz-Pawlak; Barbara Palys; Krzysztof Biesiada; Andrzej R. Olszyna; Elzbieta Malinowska (pp. 137-144).

In this work, a new concept of the solid-state sensors free from EMF instabilities is proposed. In order to prevent the formation of an aqueous layer underneath the ion-selective membrane, instead of improving the hydrophobicity of the monolayer, the moieties terminated with acrylate groups were incorporated within the redox-active monolayer structure. It allowed to “sew” all phases of the sensor (i.e., the transducer, the intermediate layer and the ion-selective membrane) and to obtain a stable and durable ion-selective sensor. It is shown that newly designed monolayer containing both the ferrocene- and the acrylate-terminated molecules does not affect the working parameters of the electrode, such as selectivity or the slope of the calibration curve, although the EMF drift of the sensor is significantly reduced to 0.2mV per day.

Keywords: Solid-state ion-selective sensors; Redox-active intermediate monolayer; Polyacrylate-based membrane; Potential stability

Evaluation of liquid–liquid microextraction using polypropylene microporous membranes for the determination of organophosphorus flame retardants and plasticizers in water samples by M. García-López; I. Rodríguez; R. Cela (pp. 145-153).

In this work, the suitability of the microporous membrane liquid–liquid extraction (MMLLE) technique for the concentration of several organophosphate esters (OPs) in water samples is assessed. Analytes were first extracted into a few microlitres of an organic solvent, immobilized in the pores of a hollow polypropylene membrane, and then determined by gas chromatography with nitrogen–phosphorus detection (GC–NPD). Main parameters controlling the efficiency of the extraction step were identified and their effects on the performance of the technique discussed. Under final working conditions, 2cm long polypropylene membranes, containing about 7μL of octanol in the pores, were dipped in a glass vial filled with 115mL of water with a 30% of sodium chloride. Extractions were carried out for 12h, at room temperature, under magnetic stirring. After that, analytes were recovered from the membrane with 0.2mL of ethyl acetate. This extract was mixed with the internal standard (50μL of a tripentyl phosphate solution in the same solvent) and finally reduced to ca. 50μL. Overall enrichment factors for the optimized method ranged from 35 to 1400 times, and the achieved limits of quantification from 0.008 to 0.12ngmL⁻¹, depending on the considered compound. Globally, the method showed an acceptable linearity and precision for all species, except for tris(2-ethylhexyl) phosphate (TEHP). Performance of the MMLLE approach is compared with that reported for other solid- and liquid-phase microextraction techniques and its suitability for the analysis of real water samples discussed.

Keywords: Microporous membrane liquid–liquid extraction; Organophosphate compounds; Flame retardants; Water samples

Simultaneous isolation of six fluoroquinolones in serum samples by selective molecularly imprinted matrix solid-phase dispersion by Hanwen Sun; Fengxia Qiao; Guangyu Liu; Shuxuan Liang (pp. 154-159).

A simple and sensitive method for the simultaneous determination of six fluoroquinolones from serum samples was developed by selective molecularly imprinted matrix solid-phase dispersion (MI-MSPD) coupled with chromatographic separation. By using ethylene glycol dimethacrylate as crosslinker and reformative methanol–water system as reaction medium, the improved water-compatible imprinted polymers were synthesized which show higher affinity to template and its analogues in aqueous environment. The molecularly imprinted polymers (MIPs) were applied as the selective dispersant of matrix solid-phase dispersion (MSPD) could selectively extracted the six fluoroquinolones from serum, while interferences originated from serum matrices were eliminated simultaneously. Good linearity was obtained in a range of 0.05–100μgmL⁻¹ with the correlation coefficients >0.999. The average recoveries of the six fluoroquinolones at four different spiked levels (0.25–10μgmL⁻¹) were ranged from 72.2% to 114.1% with the relative standard deviations less than 6.6%. This method is simple and sensitive, and can be used as an alternative tool to the existing HPLC methods for analyzing the residues of fluoroquinolones in biological samples.

Keywords: Molecularly imprinted polymer; Selective matrix solid-phase dispersion; Six fluoroquinolones; Serum samples

Monitoring of sulfonamide antibacterial residues in milk and egg by polymer monolith microextraction coupled to hydrophilic interaction chromatography/mass spectrometry by Ming-Ming Zheng; Man-Yu Zhang; Guang-Yu Peng; Yu-Qi Feng (pp. 160-172).

A simple, rapid, and sensitive method for the determination of traces of thirteen sulfonamide antibacterials in milk and eggs is presented. This method is based on the combination of polymer monolith microextraction (PMME) technique with hydrophilic interaction chromatography/mass spectrometry (HILIC/MS). The extraction was performed with a poly(methacrylic acid-ethylene glycol dimethacrylate) monolithic capillary column while the subsequent separation was carried out on a Luna NH₂ column by HILIC. To obtain optimum results, several parameters relating to HILIC and PMME were investigated. After optimization, acetonitrile (contain 0.05% formic acid, v/v) was used as the elution solution, which was well compatible with the mobile phase in HILIC. Good linearities were obtained for thirteen SAs with the correlation coefficients ( R²) above 0.997. The limits of detection (S/N=3) of the method were found to be 0.4–5.7ngmL⁻¹ of SAs in whole milk and 0.9–9.8ngg⁻¹ of SAs in eggs. The recoveries of thirteen SAs in two matrices ranged from 80.4 to 119.8%, with relative standard deviations less than 11.8%.

Keywords: Polymer monolith microextraction; Hydrophilic interaction chromatography–electrospray ionization mass spectrometry; Sulfonamide antibacterial; Milk; Egg

Flow injection-photoinduced-chemiluminescence determination of ziram and zineb by J.L. López Paz; M. Catalá-Icardo (pp. 173-179).

A simple, sensitive and rapid method for the determination of the pesticides ziram and zineb was described. This new method was based on the coupling of FIA methodology and direct chemiluminescent detection; this approach had not been used up to now with these pesticides. The additional use of an ‘on line’ photochemical reaction, which was performed by using a photoreactor consisting of a long piece of PTFE helically coiled around a 15W low-pressure lamp, increased by a factor >20 the chemiluminometric response of the pesticides. An additional 3-fold improvement in the analytical signal was also achieved by using quinine as sensitizer. The obtained throughputs were very high (121 and 101h⁻¹ for ziram and zineb, respectively); this feature together with its low limit of detection (1ngmL⁻¹) makes this method particularly well suited to routine analyses of environmental samples. On the other hand, its applicability to two members of the dithiocarbamate family of pesticides, makes it promising for the determination of the rest of the members of this family. The method was demonstrated by application to spiked water samples from different origins (ground, river and irrigation).

Keywords: Chemiluminescence; Flow injection; Ziram; Zineb; Photochemical

A microchip-based flow injection-amperometry system with mercaptopropionic acid modified electroless gold microelectrode for the selective determination of dopamine by Yi Wang; Jie Luo; Hengwu Chen; Qiaohong He; Nin Gan; Tianhua Li (pp. 180-187).

A novel chip-based flow injection analysis (FIA) system has been developed for automatic, rapid and selective determination of dopamine (DA) in the presence of ascorbic acid (AA). The system is composed of a polycarbonate (PC) microfluidic chip with an electrochemical detector (ED), a gravity pump, and an automatic sample loading and injection unit. The selectivity of the ED was improved by modification of the gold working microelectrode, which was fabricated on the PC chip by UV-directed electroless gold plating, with a self-assembled monolayer (SAM) of 3-mercaptopropionic acid (MPA). Postplating treatment methods for cleaning the surface of electroless gold microelectrodes were investigated to ensure the formation of high quality SAMs. The effects of detection potential, flow rate, and sampling volume on the performance of the chip-based FIA system were studied. Under optimum conditions, a detection limit of 74nmolL⁻¹ for DA was achieved at the sample throughput rate of 180h⁻¹. A RSD of 0.9% for peak heights was observed for 19 runs of a 100μmolL⁻¹ DA solution. Interference-free determination of DA could be conducted if the concentration ratio of AA–DA was no more than 10.

Keywords: Microfluidic chip; Flow injection analysis; Electrochemical detection; Self-assembled monolayer; Dopamine

Multiresidue determination of triarylmethane and phenothiazine dyes in fish tissues by LC–MS/MS by Jonathan A. Tarbin; Danny Chan; George Stubbings; Matthew Sharman (pp. 188-194).

The occurrence of residues of malachite green and its leuco-metabolite in tissues of farmed fish for human consumption have long been of concern and there is extensive literature on methods of analysis and surveillance for these compounds. Recently, concern has been expressed that the use of other related compounds in place of malachite green may go undetected. This paper describes a new method for extending the range of triarylmethane and related phenothiazine dyes that can be detected in fish. In this procedure 13 parent compounds are monitored, with any potential leuco-forms being oxidized back to the parent prior to determination. The method utilizes a buffer–acetonitrile extraction followed by liquid–liquid extraction. Oxidant is added and the extracts further purified by cation exchange chromatography. Final determination is carried out using LC–MS/MS. The method has been validated to the standards of Commission Decision 2002/657/EC.

Keywords: Fish; Malachite green; Dyes; Analysis

Fluorescence enhancement effect for the determination of DNA with calcein–cetyl trimethyl ammonium bromide system by Fengshan Yu; Yanbin Ding; Yongwei Gao; Shishi Zheng; Fang Chen (pp. 195-200).

A new spectrofluorimetric method was developed for the determination of trace amounts of DNA using the calcein as a fluorescent probe. In the presence of appropriate amounts of the cationic surfactant cetyl trimethyl ammonium bromide (CTAB), the anionic dye calcein dimerizes. The weak fluorescence intensity of the dimer was enhanced by adding DNA at pH 6–7. The interaction between calcein–CTAB and DNA was studied on the basis of this behavior and a new method was developed for determining DNA. Under the optimal conditions, the enhanced fluorescence intensity was in proportion to the concentration of DNA in the range of 4.0×10⁻⁶ to 8.0×10⁻⁵gL⁻¹ for fsDNA and thermally denatured ctDNA (4.5×10⁻⁶ to 9.0×10⁻⁵gL⁻¹). The detection limits (S/N=3) were 2.0×10⁻⁶ and 2.2×10⁻⁶gL⁻¹, respectively. This method was used for determining the concentration of DNA in synthetic samples with satisfactory results.

Keywords: Calcein; Deoxyribonucleic acid; Spectrofluorimetry; Cetyl trimethyl ammonium bromide

Anti-Her-2 monoclonal antibody conjugated polymer fluorescent nanoparticles probe for ovarian cancer imaging by Xu Hun; Zhujun Zhang; Liang Tiao (pp. 201-206).

Fluorescent nanoparticles (FNPs) with unique optical properties may be useful as biosensors in living cancer cell imaging and cancer targeting. A novel kind of polymer fluorescent nanoparticles (PFNPs) was synthesized and its application for ovarian cancer imaging with fluorescence microscopy imaging technology was presented in this study. The PFNPs were synthesized with precipitation polymerization by using methacrylic acid (MAA) as monomer, trimethylolpropane trimethacrylate (Trim) as cross-linker, azobisisobutyronitrile (AIBN) as radical initiator and butyl rhodamine B (BTRB) as fluorescent dye. And the fluorescent dye was embedded into the three-dimensional network of the polymer when the polymer was produced. With this method the PFNPs can be prepared easily. And then the PFNPs were successfully modified with anti-Her-2 monoclonal antibody. The fluorescence probe based on anti-Her-2 monoclonal antibody conjugated PFNPs has been used to detect ovarian cancer cells with fluorescence microscopy imaging technology. The experimental results demonstrate that the anti-Her-2 monoclonal antibody conjugated PFNPs can effectively recognize ovarian cancer cells and exhibit good sensitivity and exceptional photostability, which would provide a novel way for the diagnosis and curative effect observation of ovarian cancer cells.

Keywords: Precipitation polymerization; Polymer fluorescent nanoparticles (PFNPs); Anti-Her-2 monoclonal antibody; Ovarian cancer; Fluorescence microscopy imaging

Computer screen photo-excited surface plasmon resonance imaging by Daniel Filippini; Fredrik Winquist; Ingemar Lundström (pp. 207-214).

Angle and spectra resolved surface plasmon resonance (SPR) images of gold and silver thin films with protein deposits is demonstrated using a regular computer screen as light source and a web camera as detector. The screen provides multiple-angle illumination, p-polarized light and controlled spectral radiances to excite surface plasmons in a Kretchmann configuration. A model of the SPR reflectances incorporating the particularities of the source and detector explain the observed signals and the generation of distinctive SPR landscapes is demonstrated. The sensitivity and resolution of the method, determined in air and solution, are 0.145nmpixel⁻¹, 0.523nm, 5.13×10⁻³RIUdegree⁻¹ and 6.014×10⁻⁴RIU, respectively, encouraging results at this proof of concept stage and considering the ubiquity of the instrumentation.

Keywords: Surface plasmon resonance; Optical sensing; Computer screen photo-assisted technique; Biosensors; Sensors

Differential scanning calorimetry: A potential tool for discrimination of olive oil commercial categories by Emma Chiavaro; Maria Teresa Rodriguez-Estrada; Carlo Barnaba; Elena Vittadini; Lorenzo Cerretani; Alessandra Bendini (pp. 215-226).

Differential scanning calorimetry thermograms of five commercial categories of olive oils (extra virgin olive oil, olive oil, refined olive oil, olive-pomace oil and refined olive-pomace oil) were performed in both cooling and heating regimes. Overlapping transitions were resolved by deconvolution analysis and all thermal properties were related to major (triacylglycerols, total fatty acids) and minor (diacylglycerols, lipid oxidation products) chemical components.All oils showed two well distinguishable exothermic events upon cooling. Crystallization enthalpies were significantly lower in olive oils due to a more ordered crystal structure, which may be related to the higher triolein content. Pomace oils exhibited a significantly higher crystallization onset temperature and a larger transition range, possibly associated to the higher amount of diacylglycerols. Heating thermograms were more complex: all oils exhibited complex exo- and endothermic transitions that could differentiate samples especially with respect to the highest temperature endotherm.These preliminary results suggest that both cooling and heating thermograms obtained by means of differential scanning calorimetry may be useful for discriminating among olive oils of different commercial categories.

Keywords: Extra virgin olive oil; Olive oil; Olive-pomace oil; Differential scanning calorimetry; Thermal properties; Chemical composition

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Analytica Chimica Acta (v.625, #2)