Check out our New Publishers' Select for Free Articles

Analytica Chimica Acta (v.662, #2)

Editorial Board (pp. i).

Review: Carbon nanotube based electrochemical sensors for biomolecules by Christopher B. Jacobs; M. Jennifer Peairs; B. Jill Venton (pp. 105-127).

Carbon nanotubes (CNTs) have been incorporated in electrochemical sensors to decrease overpotential and improve sensitivity. In this review, we focus on recent literature that describes how CNT-based electrochemical sensors are being developed to detect neurotransmitters, proteins, small molecules such as glucose, and DNA. Different types of electrochemical methods are used in these sensors including direct electrochemical detection with amperometry or voltammetry, indirect detection of an oxidation product using enzyme sensors, and detection of conductivity changes using CNT-field effect transistors (FETs). Future challenges for the field include miniaturizing sensors, developing methods to use only a specific nanotube allotrope, and simplifying manufacturing.

Keywords: Field effect transistor sensor; Enzyme sensor; Dopamine; Virus; Immunosensor; Immunoglobulin

Comparison of single and sequential extraction procedures for the study of rare earth elements remobilisation in different types of soils by Chebrolu Rama Mohan Rao; Angels Sahuquillo; Jose Fermin Lopez-Sanchez (pp. 128-136).

With the continual increase in the utilisation of rare earth elements (REE) for industrial and agricultural purposes, research into the environmental and biogeochemical behaviour of REE had attracted much interest in recent times. This study principally describes the distribution of REE in four different types of soils like lateritic soil (S-1), in situ natural soil (S-2), soil contaminated by mining activity (S-3) and accidentally polluted soil (S-4) utilizing the optimised BCR sequential extraction procedure and partial extractions with various types of single extractants such as unbuffered salt solutions 0.1M NaNO₃, 0.01M CaCl₂, 1M NH₄NO₃; complexing agents 0.005M DTPA and 0.05M EDTA; acid solutions 0.43M CH₃COOH and 1M HCl. Comparison of the sum of the four BCR fractions, which included an aqua regia attack on the residue, with the pseudo-total aqua regia digest values to assess the accuracy of the BCR partioning approach has been undertaken. Partial extraction results with several single extractants have also been reported for all the REE elements including yttrium which have been analysed by the optimised BCR procedure. Results obtained after 24h extraction with each of the single extractant have also been discussed. The extraction with 1M HCl during 24h yielded similar quantities of REE as those released under the combined steps of 1, 2 and 3 of the BCR sequential extraction for all the four different type of soil samples indicating that this reagent can be used successfully to estimate the total extractable contents of REE in various types of soil samples.

Keywords: Bureau Communautaire de Références sequential extraction; Single extraction; Soil; Inductively copupled plasma - mass spectrometry; Rare earth elements

Feature extraction and selection from volatile compounds for analytical classification of Chinese red wines from different varieties by Jian Zhang; Li Li; Nianfa Gao; Depei Wang; Qiang Gao; Shengping Jiang (pp. 137-142).

This work was undertaken to evaluate whether it is possible to determine the variety of a Chinese wine on the basis of its volatile compounds, and to investigate if discrimination models could be developed with the experimental wines that could be used for the commercial ones. A headspace solid-phase microextraction gas chromatographic (HS-SPME-GC) procedure was used to determine the volatile compounds and a blind analysis based on Ac/Ais (peak area of volatile compound/peak area of internal standard) was carried out for statistical purposes. One way analysis of variance (ANOVA), principal component analysis (PCA) and stepwise linear discriminant analysis (SLDA) were used to process data and to develop discriminant models. Only 11 peaks enabled to differentiate and classify the experimental wines. SLDA allowed 100% recognition ability for three grape varieties, 100% prediction ability for Cabernet Sauvignon and Cabernet Gernischt wines, but only 92.31% for Merlot wines. A more valid and robust way was to use the PCA scores to do the discriminant analysis. When we performed SLDA this way, 100% recognition ability and 100% prediction ability were obtained. At last, 11 peaks which selected by SLDA from raw analysis set had been identified. When we demonstrated the models using commercial wines, the models showed 100% recognition ability for the wines collected directly from winery and without ageing, but only 65% for the others. Therefore, the varietal factor was currently discredited as a differentiating parameter for commercial wines in China. Nevertheless, this method could be applied as a screening tool and as a complement to other methods for grape base liquors which do not need ageing and blending procedures.

Keywords: Headspace solid-phase microextraction; Wine; Volatile compounds; Principal component analysis; Stepwise linear discriminant analysis; Classification

Self-modeling curve resolution techniques applied to comparative analysis of volatile components of Iranian saffron from different regions by Mehdi Jalali-Heravi; Hadi Parastar; Heshmatollah Ebrahimi-Najafabadi (pp. 143-154).

Volatile components of saffron from different regions of Iran were extracted by ultrasonic-assisted solvent extraction (USE) and were analyzed by gas chromatography–mass spectrometry (GC–MS). Self-modeling curve resolution (SMCR) was proposed for resolving the co-eluted GC–MS peak clusters into pure chromatograms and mass spectra. Multivariate curve resolution-objective function minimization (MCR-FMIN) and multivariate curve resolution-alternating least square (MCR-ALS) were successfully used for this purpose. The accuracy of the qualitative and quantitative results was improved considerably using SMCR techniques. Comparison of the results of saffron from different regions of Iran showed that their volatile components are different from chemical components and relative percentages points of view. Safranal is the main component of all samples. In addition, 4-hydroxy-2,6,6-trimethyl-1-cyclohexene-1-carboxaldehyde (HTCC), 2(5H)-furanone, 2,4,4-trimethyl-3-carboxaldehyde-5-hydroxy-2,5-cyclohexadien-1-one and 2(3H)-furanone, dihydro-4-hydroxy were common in all samples with high percentages. The results proved that combining of SMCR techniques with USE-GC–MS produces a powerful tool for the analysis of the complex samples.

Keywords: Self-modeling curve resolution; Saffron; Ultrasonic solvent extraction; Objective function minimization; Alternating least square; Gas chromatography–mass spectrometry

Highly selective ionic liquid-based microextraction method for sensitive trace cobalt determination in environmental and biological samples by Paula Berton; Rodolfo G. Wuilloud / (pp. 155-162).

A simple and rapid dispersive liquid–liquid microextraction procedure based on an ionic liquid (IL-DLLME) was developed for selective determination of cobalt (Co) with electrothermal atomic absorption spectrometry (ETAAS) detection. Cobalt was initially complexed with 1-nitroso-2-naphtol (1N2N) reagent at pH 4.0. The IL-DLLME procedure was then performed by using a few microliters of the room temperature ionic liquid (RTIL) 1-hexyl-3-methylimidazolium hexafluorophosphate [C₆mim][PF₆] as extractant while methanol was the dispersant solvent. After microextraction procedure, the Co-enriched RTIL phase was solubilized in methanol and directly injected into the graphite furnace. The effect of several variables on Co–1N2N complex formation, extraction with the dispersed RTIL phase, and analyte detection with ETAAS, was carefully studied in this work. An enrichment factor of 120 was obtained with only 6mL of sample solution and under optimal experimental conditions. The resultant limit of detection (LOD) was 3.8ngL⁻¹, while the relative standard deviation (RSD) was 3.4% (at 1μgL⁻¹ Co level and n=10), calculated from the peak height of absorbance signals. The accuracy of the proposed methodology was tested by analysis of a certified reference material. The method was successfully applied for the determination of Co in environmental and biological samples.

Keywords: 1-Hexyl-3-methylimidazolium hexafluorophosphate; Room temperature ionic liquid; Microextraction; Cobalt; Environmental and biological samples

Integrated liquid chromatography–heated nebulizer microchip for mass spectrometry by Markus Haapala; Ville Saarela; Jaroslav Pól; Kai Kolari; Tapio Kotiaho; Sami Franssila; Risto Kostiainen (pp. 163-169).

A new integrated microchip for liquid chromatography–mass spectrometry (LC–MS) is presented. The chip is made from bonded silicon and glass wafers with structures for a packed LC column channel, a micropillar frit, a channel for optional optical detection, and a heated vaporizer section etched in silicon and platinum heater elements on the glass cover. LC eluent is vaporized and mixed with nebulizer gas in the vaporizer section and the vapor is sprayed out from the chip. Nonpolar and polar analytes can be efficiently ionized in the gas phase by atmospheric pressure photoionization (APPI) as demonstrated with polycyclic aromatic hydrocarbons (PAHs) and selective androgen receptor modulators (SARMs). This is not achievable with present LC–MS chips, since they are based on electrospray ionization, which is not able to ionize nonpolar compounds efficiently. The preliminary quantitative performance of the new chip was evaluated in terms of limit of detection (down to 5ngmL⁻¹), linearity ( r>0.999), and repeatability of signal response (RSD=2.6–4.0%) and retention time (RSD=0.3–0.5%) using APPI for ionization and PAHs as standard compounds. Determination of fluorescent compounds is demonstrated by using laser-induced fluorescence (LIF) for detection in the optical detection channel before the vaporizer section.

Keywords: Liquid chromatography; Mass spectrometry; Microchip; Miniaturization; Atmospheric pressure ionization

Fluorescence single-molecule counting assays for protein quantification using epi-fluorescence microscopy with quantum dots labeling by Dafeng Jiang; Chunxia Liu; Lei Wang; Wei Jiang (pp. 170-176).

A single-molecule counting approach for quantifying the antibody affixed to a surface using quantum dots and epi-fluorescence microscopy is presented. Modifying the glass substrates with carboxyl groups provides a hydrophilic surface that reacts with amine groups of an antibody to allow covalent immobilization of the antibody. Nonspecific adsorption of single molecules on the modified surfaces was first investigated. Then, quantum dots were employed to form complexes with surface-immobilized antibody molecules and used as fluorescent probes for single-molecule imaging. Epi-fluorescence microscopy was chosen as the tool for single-molecule fluorescence detection here. The generated fluorescence signals were taken by an electron multiplying charge-coupled device and were found to be proportional to the sample concentrations. Under optimal conditions, a linear response range of 5.0×10⁻¹⁴–3.0×10⁻¹²molL⁻¹ was obtained between the number of single molecules and sample concentration via a single-molecule counting approach.

Keywords: Single-molecule counting; Quantum dot; Epi-fluorescence microscopy; Surface modification; Antibody

Immunochemical determination of oxytetracycline in fish: Comparison between enzymatic and time-resolved fluorometric assays by Consuelo Cháfer-Pericás; Ángel Maquieira; Rosa Puchades; Javier Miralles; Amelia Moreno; Nuria Pastor-Navarro; Francisco Espinós (pp. 177-185).

An indirect competitive enzyme-linked immunosorbent assay (ELISA) with photometric detection of horseradish peroxidase (HRP) activity, was developed in plate to detect oxytetracycline (OTC) in Gilthead sea bream ( Sparus aurata) samples. The results were compared to those obtained by time-resolved fluoroimmunoassay (TR-FIA) using a secondary antibody with coproporphyrin of platinum (II) (PtCP) as marker. The limits of detection obtained in fish extract were 16 and 0.08μgkg⁻¹ for photometric and fluorometric detections, respectively; therefore, they were suitable for fish quality control according to the maximum residue level established by the European Union.An extraction procedure using methanol:water 70:30 (v/v)+1mL EDTA 0.1M, and different clean-up procedures based on solid-phase extraction (C₁₈, polymeric reversed phase, SCX, Si) was assayed. The matrix effects were overcome by means of an average tetracycline-free fish extract calibration curve used for quantification.The OTC optimized ELISA can also be applied to determine tetracycline and chlortetracycline residues with good results. Thus, the developed immunoassay could be considered as a generic assay for the most used tetracyclines in aquaculture antibiotic treatments.In order to confirm the utility of the developed immunoassay as a semi-quantitative methodology, fish samples obtained from different supermarkets were analyzed. Results correlate well with those obtained with a reference HPLC method.

Keywords: Tetracycline; Fish; Enzyme-linked immunosorbent assay; Time-resolved fluoroimmunoassay

Selective detection and estimation of C-reactive protein in serum using surface-functionalized gold nano-particles by Vidya Raj; K. Sreenivasan (pp. 186-192).

A new method for the detection of C-reactive protein (CRP) in serum using functionalized gold nano-particles (GNP) is reported. The affinity towards CRP is imparted to GNP by tethering O-phosphorylethanolamine (PEA) onto their surface. GNP and modified GNP were characterized using TEM, particle size analysis, zeta potential measurements, absorption spectroscopy and FT-IR techniques. The event of binding of CRP onto the PEA-GNP is followed by visibly observable colour change. We observed a red shift as well as a decrease in absorption in the plasmon peak of the modified GNP with the concentration of CRP. When the concentration of CRP exceeded 450ngmL⁻¹, particles were aggregated and the solution became turbid. The method exhibited a linear range for CRP from 50 to 450ngmL⁻¹ with a detection limit of 50ngmL⁻¹. The colour change and the variation in absorption of the GNP were highly specific to CRP even in the presence of albumin. We estimated CRP in blood serum collected from patients and the results obtained compared well with the estimation using the technique of nephelometry based on the antibody–antigen interaction.

Keywords: Gold nano-particles; O-phosphorylethanolamine; Serum; C-reactive protein

Characterization of exopolysaccharides in marine colloids by capillary electrophoresis with indirect UV detection by Qiuju Gao; Musie Araia; Caroline Leck; Åsa Emmer (pp. 193-199).

A method was established using capillary electrophoresis with indirect UV detection for analysis of monosaccharides liberated from exopolysaccharides by acidic hydrolysis. Tangential flow filtration was used to isolate high molecular weight polysaccharides from seawater. The capillary electrophoresis method included the use of a background electrolyte consisting of 2,6-dimethoxyphenol and cetyltrimethylammonium bromide. Several neutral sugars commonly existing in marine polysaccharides were separated under optimized conditions. The relative standard deviations were between 1.3% and 2.3% for relative migration time and 1.3–2.5% for peak height. Detection limits (at S/N 3) were in the range of 27.2–47.8μM. The proposed approach was applied to the analysis of hydrolyzed colloidal polysaccharides in seawater collected from the Baltic Sea. Nanomolar levels of liberated monosaccharides in seawater samples can be detected by preconcentration up to 30,000 times.

Keywords: Exopolysaccharide; Capillary electrophoresis; Extracellular polymeric substances; Marine colloid

A simple method for preparation of macroporous polydimethylsiloxane membrane for microfluidic chip-based isoelectric focusing applications by Junjie Ou; Carolyn L. Ren; Janusz Pawliszyn (pp. 200-205).

A new, simple method was reported to prepare PDMS membranes with micrometer size pores for microfluidic chip applications. The pores were formed by adding polystyrene and toluene into PDMS prepolymer solution prior to spin-coating and curing. The resulting PDMS membrane has a thickness of around 10μm and macropores with a diameter ranging from 1 to 2μm measured using scanning electron microscope (SEM) imaging. This PDMS membrane was validated by integrating it with PDMS microfluidic chips for protein separation using isoelectric focusing mechanism coupled with whole channel imaging detection (IEF-WCID). It has been shown that five standard p I markers and a mixture of two proteins, myoglobin and β-lactoglobulin, can be separated using these chips. The results indicated that this macroporous PDMS membrane can replace the dialysis membrane in PDMS chips for the IEF-WCID technique. The preparation method of macroporous PDMS membrane may be potentially applied in other fields of microfluidic chips.

Keywords: Microfluidic chip; Isoelectric focusing; Protein separation; Polydimethylsiloxane membrane; Whole channel imaging detection

Development of a novel fluorescent tag O-2-[aminoethyl]fluorescein for the electrophoretic separation of oligosaccharides by Artaches A. Kazarian; Jason A. Smith; Emily F. Hilder; Michael C. Breadmore; Joselito P. Quirino; James Suttil (pp. 206-213).

This study describes the development of a novel fluorescent tag, O-2-[aminoethyl]fluorescein, for the separation of sugars by capillary electrophoresis with fluorescence detection using an argon ion laser. The tag was synthesised using three consecutive steps namely: esterification, alkylation and hydrolysis, specifically designed to offer a flexible way in which to make an assortment of fluorescent tags from cheap and readily available starting reagents (typically less than $1perg of fluorescent tag). Via this flexible synthetic pathway, O-2-[aminoethyl]fluorescein was designed and synthesised with a spacer group to lower steric effects between the fluorescein backbone and the reducing end of the carbohydrate which were anticipated to improve the reactivity of the tag. The newly synthesised tag, O-2-[aminoethyl]fluorescein was evaluated against structurally similar commercial fluorescent motifs namely fluorescent 5-aminomethylfluorescein and non-fluorescent 5-aminofluorescein. Kinetic studies indicated that O-2-[aminoethyl]fluorescein showed similar labeling efficiencies as 5-aminomethylfluorescein, but were achieved in only 30min, supporting the notion of improved reactivity of the spacer group. The sensitivity of O-2-[aminoethyl]fluorescein was evaluated using maltoheptaose with a detection limit of 1nM obtained, which was slightly higher than that of 0.3nM obtained with 5-aminomethylfluorescein, and was due to its lower quantum yield (0.24) when conjugated to the sugar. The separation performance of the tag was also benchmarked with the two commercial reagents using a range of corn syrup oligosaccharides, from 4 to 10 glucose units, typically found in rice starch. Separations were performed using an electrolyte containing 100mM boric acid, tris at pH 8.65 as background electrolyte, 30kV applied voltage, 50μm I.D.×40cm (30cm effective length) capillary. The novel tag showed better resolution of small oligosaccharides, G3 and G4, than the other two reagents, but slightly worse resolution for the longer oligosaccharides, most likely due to the monovalent charge state of the O-2-[aminoethyl]fluorescein compared to the divalent charge of the other two tags.

Keywords: Capillary electrophoresis (CE); Laser induced fluorescence (LIF); Carbohydrate; Derivatisation; O-2-[aminoethyl]fluorescein

Sections

Personal tools

Analytica Chimica Acta (v.662, #2)

Sections

Personal tools

Local resources

Analytica Chimica Acta (v.662, #2)