Traceability of honey origin based on volatiles pattern processing by artificial neural networks

Head-space solid-phase microextraction (HS-SPME)-based procedure, coupled to comprehensive two-dimensional gas chromatography–time-of-flight mass spectrometry (GC × GC–TOF-MS), was employed for fast characterisation of honey volatiles. In total, 374 samples were collected over two production seasons in Corsica (n = 219) and other European countries (n = 155) with the emphasis to confirm the authenticity of the honeys labelled as “Corsica” (protected denomination of origin region). For the chemometric analysis, artificial neural networks with multilayer perceptrons (ANN-MLP) were tested. The best prediction (94.5%) and classification (96.5%) abilities of the ANN-MLP model were obtained when the data from two honey harvests were aggregated in order to improve the model performance compared to separate year harvests.     

Comparative chemometric analyses of geographic origins and compositions of lavandin var. Grosso essential oils by mid infrared spectroscopy and gas chromatography

Lavandin, a sterile hybrid of Lavandula angustifolia P. Mill. × Lavandula latifolia (L.f.) Medikus (Lamiaceae) is a plant widely cultivated for essential oil production in the South of France. Chemometric treatment by mid-infrared (MID-IR) spectroscopy data was assessed for the differentiation of Grosso Lavandin Essential Oils of Controlled Area (GLEOCA) and results were compared to those obtained by gas chromatography for MID-IR short time technique validation. The quantification of the main 13 hydrocarbons and oxygenated compounds generally controlled by industrial perfumers in GLEOCA samples (n = 83) of three geographic origins: “Simiane”, “Puimoisson” (with two producers) and “Richerenches” and their classification were successfully obtained by partial least square discriminant analysis (PLS-DA) by comparison with gas chromatography. The best prediction results were obtained using first derivate spectral data in the 1800-700 cm⁻¹ range. The spectroscopic interpretation of regression vectors showed that each geographic origin was correlated to components of GLEOCA. Chemometric MID-IR spectra treatments allowed us to obtain similar results than those obtained by time consuming analytical techniques such as GC and therefore constitute a robust and help fast method for authentication of GLEOCA and should be extended to other essential oils for authentication of geographic origin.     

Development of a sampling and flow injection analysis technique for iron determination in the sea ice environment

A trace metal clean method for sampling and analysis of iron is set up and applied to sea ice and its associated snow, brine, and underlying seawater sampled during the Antarctic expedition “ARISE in the East” (Antarctic Remote Ice Sensing Experiment, AA03-V1, September-October 2003, 64-65°S/112-119°E, RV Aurora Australis). For clean sampling, a non-contaminating electropolished stainless steel ice corer is designed in conjunction with a polyethylene lathe equipped with Ti chisels to remove possibly contaminated outer layers of ice cores. A portable peristaltic pump with clean tubing is used on the ice to sample the underlying seawater (interface ice-water = 0, 1 and 30 m) and sea ice brine from access holes. Considering the extreme range of salinities (1-100) and Fe concentrations (0.1-100 nM) previously observed in similar environments, it is of paramount importance to set up a simple and sensitive Fe analyser adapted to such gradients. We use a flow injection analysis (FIA) technique and successfully demonstrate its capability to measure Fe concentrations directly in the sample without an on-line preconcentration/matrix separation step. We test the sensitivity, accuracy, precision and long-term stability of the analytical procedure. Also we explore and remediate interferences from a suite of other trace elements, such as Ni, Cd, Cr, Mn, Cu, Zn and Co. Analysis of reference materials NASS-5 and CASS-3 gives a good agreement with the certified values. Repeated measurements over a period of 5 months of an “in-house” Antarctic seawater standard yields a concentration of 1.02 ± 0.07 nM (n = 17, 1σ). The detection limit (3σ of the blank) is on average 0.12 nM. We report here results of the Fe distribution in sea ice that are in good agreement with previously published data. To our knowledge, this work provides the first complete profiles of total dissolvable and dissolved Fe in sea ice.     

Morphology of polystyrene-block-poly(styrene-co-acrylonitrile) and polystyrene-block-poly(styrene-co-acrylonitrile-co-5-vinyltetrazole) diblock copolymers prepared by nitroxide-mediated radical polymerization and “click” chemistry

Well-defined polystyrene-block-poly(styrene-co-acrylonitrile) PS-block-P(S-co-AN) and poly(styrene-co-acrylonitrile-co-5-vinyltetrazole) PS-block-P(S-co-AN-co-5VT) block copolymers with various content of acrylonitrile units in the statistical block were synthesized by nitroxide mediated radical polymerization (NMRP) and post-functionalized using efficient “click” chemistry process. In the second step, acrylonitrile units were successfully modified using 1,3-dipolar cycloaddition (“click” chemistry) type polymer analogue reaction. The original pristine diblock copolymers can be molecularly dissolved in THF and dioxane while the “tetrazolated” versions aggregate to clusters as determined by dynamic light scattering (DLS). Small-angle X-ray scattering (SAXS) and Transmission Electron Microscopy (TEM) revealed ordered lamellar morphology with interlamellar spacing d = 60 nm increasing to d = 80 nm for “tetrazolated” diblock copolymers. The morphological features of diblock copolymer thin layers observed by Atomic Force Microscopy (AFM) depend on the tunable content of both acrylonitrile and 5-vinyltetrazole units and on the quality (polarity) of the solvents used.     

Characterisation of a hydraulic high-pressure sample introduction assisted flow injection-inductively coupled plasma time-of-flight mass spectrometry system and its application to the analysis of biological samples

A flow injection (FI) method was developed using hydraulic high-pressure nebulization as a sample introduction system, coupled to inductively coupled plasma time-of-flight mass spectrometer (ICP-TOFMS) for rapid and simultaneous determination of 19 elements. The operating conditions of the system (analyte flow rate, heating and cooling temperatures of the desolvation module, carrier gas flow rate) for the simultaneous determination of 19 analytes were optimised. The optimum parameters of the sample introduction system were found to be 1.4 ml min⁻¹ and 1.35 l min⁻¹ for the analyte solution and nebulizer flow rates, respectively. A compromised condition for heating and cooling stage temperatures of 170 and −5 °C was chosen. The detection limits were compared to those obtained by using ICP-TOFMS with alternative sample introduction techniques e.g. conventional nebulization, flow injection chemical hydride generation (FI-CHG) and the obtained results were comparable or better than those resulting from alternative sample introduction. Applying the optimised conditions the simultaneous determination of Ag, As, Ba, Cd, Co, Cu, Ga, In, Li, Mn, Mo, Pb, Sb, Se, Sn, Sr, Tl, V and Zn was carried out. Absolute detection limits (3σ) in the range of 2-750 pg and precision between 0.5 and 9.6% from five replicate measurements of 10 ng ml⁻¹ multielemental sample solutions were achieved by using a 200 μl sample loop. The developed method was applied for the analysis of certified reference materials of biological origin (TORT-2 “Lobster Hepatopancrease”, BCR-422 “Cod Muscle” and IAEA MA-B-3/TM “Fish Homogenate”), and the results showed good agreement with the certified values.     

Analysis of the radial and longitudinal effects of a planar sample in a single TE102 rectangular electron paramagnetic resonance (EPR) cavity

The response of the cavity to the rotation of a concentrically positioned planar sample of variable width, w ∈ 〈1 mm, 10 mm〉, around the common cavity-sample x-axis in a Bruker single TE₁₀₂ rectangular cavity (radial effect) has been analysed. The observed dependence of the EPR signal intensity, Ipp, on the rotation angle has a general ovaloid shape with an eccentricity, ?, which varies linearly with the width, w, of the sample, ? = 0.0246 + 0.0311 × w, correlation, R = 0.996, for samples with a width greater than 2 mm but shows a positive deviation from linearity for the 1 and 2 mm samples. The dependence of the Ipp value on the planar sample width, w, is non-linear for all polar-angle values investigated. These experimental observations are in a very good agreement with theoretical calculations in which the response is modelled using the Cassinian curves modified for planar sample geometry. Similar trends of the angular Ipp dependence were observed for any position of the planar sample as the centre was moved along the vertical x-axis of the cavity. In the longitudinal Ipp dependence for a planar sample whose length, L = 30 mm, is greater than that of the cavity, then (i) for the case where the whole cavity length is occupied by the sample a constant value for the Ipp (a plateau) is observed and (ii) for sample movement in and out of this plateau region the dependence varies according to the left and right halves of a modified “sine-squared” function. The variation in the signal amplitude along the cavity x-axis (longitudinal effect) can be calculated theoretically using a “sine-squared” curve, modified for an “over full-length cavity” planar sample. In general, the response of the cavity to a planar sample situated at any position on the common sample cavity x-axis can be represented as a product of a modified Cassinian curve and a modified “sine-squared” curve. The non-linear radial effect may give rise to serious sources of systematic error in quantitative EPR spectroscopy with planar sample geometry and shows that accurate and precise positioning of the sample in the microwave cavity is essential.     

Profiling analysis of volatile compounds from fruits using comprehensive two-dimensional gas chromatography and image processing techniques

An image processing approach originating from the proteomics field has been transferred successfully to the processing of data obtained with comprehensive two-dimensional gas chromatographic separations data. The approach described here has proven to be a useful analytical tool for unbiased pattern comparison or profiling analyses, as demonstrated with the differentiation of volatile patterns (“aroma”) from fruits such as apples, pears, and quince fruit. These volatile patterns were generated by headspace solid phase microextraction coupled to comprehensive two-dimensional gas chromatography (HS-SPME-GC × GC). The data obtained from GC × GC chromatograms were used as contour plots which were then converted to gray-scale images and analyzed utilizing a workflow derived from 2D gel-based proteomics. Run-to-run variations between GC × GC chromatograms, respectively their contour plots, have been compensated by image warping. The GC × GC images were then merged into a fusion image yielding a defined and project-wide spot (peak) consensus pattern. Within detected spot boundaries of this consensus pattern, relative quantities of the volatiles from each GC × GC image have been calculated, resulting in more than 700 gap free volatile profiles over all samples. These profiles have been used for multivariate statistical analysis and allowed clustering of comparable sample origins and prediction of unknown samples. At present state of development, the advantage of using mass spectrometric detection can only be realized by data processing off-line from the identified software packages. However, such information provides a substantial basis for identification of statistically relevant compounds or for a targeted analysis.     

Implementation of an automatic standard addition method in a flow-batch system: application to copper determination in an alcoholic beverage by atomic absorption spectrometry

A novel strategy for implementing the automatic standard addition method (SAM) is described. By using a flow-batch system that presents the intrinsic favourable characteristics of the flow and batch techniques, the proposed strategy performs fast standard additions with sufficient flexibility and versatility and employs only one standard solution per analyte. To calculate the analyte concentration, a mathematical model based on a classical SAM and flow variables of the system was developed. The proposed flow-batch SAM was applied to copper determination by flame atomic absorption spectrometry (AAS) in sugar cane-made alcoholic beverages, known as “Cachaça”, available in Brazil. A SAM has been recommended for these analyses because “Cachaças” presents a significantly different composition causing matrix effects and copper determination by calibration using matrix-matching standards can yield inaccurate results. The results show good agreement between the obtained values with the proposed flow-batch SAM and a manual SAM. The mean relative errors and overall standard deviations were always <1.0% (n=6) and 0.2 mg l⁻¹, respectively, for 1.0-7.0 mg l⁻¹ Cu. By using five standard addition levels, the sample throughput was 70 h⁻¹ and the consumption of sample and standard solution were 1.5 and 0.5 ml per analysis, respectively.     

Determination of total safranal by in situ acid hydrolysis in supercritical fluid media: Application to the quality control of commercial saffron

A procedure allowing hydrolysis reactions to be conducted in a dynamic supercritical-CO₂ medium was developed for quantifying total safranal (viz. free safranal present in the sample + safranal resulting from picrocrocin hydrolysis), which are the main component of the essential oil and responsible for the characteristic aroma of saffron. The proposed method allows total safranal amounts over the ranges 0.05-1.5 mg mL⁻¹ to be determined. The standard deviation achieved was 2%. This method was applied to the determination of safranal in natural saffron samples. The results obtained were compared with the “safranal value” total index, which is widely used as a quality measure of saffron products. The comparison revealed that the proposed method provides useful information not contained in the safranal value, based on the fact that, some samples with a high “safranal index” contain low concentrations of safranal. The proposed method is very useful for quality control in commercial saffron samples.     

Influence of the variable wall thickness of the sample tubes and a quartz Dewar on the EPR signal intensity in a single TE102 and double TE104 rectangular cavity

The response of a single TE₁₀₂ and double TE₁₀₄ rectangular cavity to the insertion of samples contained in tubes with variable wall thickness and a quartz Dewar into the cavity has been analyzed. A direct, indirect, and concurrent (positive or negative) “lens effect” inside the double TE₁₀₄ rectangular cavity is discussed. The experimental dependence of the EPR signal intensity on the wall thickness of the sample tube, δ, for the line-like samples with identical length of the sample material column, L=30 mm, recorded in the microwave cavity showed a directly proportional increase of the relative “lens effect” with the increase of the wall thickness of the tube in the interval, δ∈<0.1 mm, >0.5 mm. The insertion of the variable-temperature double-wall quartz Dewar (home-built, resonant frequency shift, ca. −300 MHz) into the single TE₁₀₂ rectangular cavity showed the same relative “lens effect”, with ca. 1.5-time increase of the EPR signal intensity, for a point-like sample and the line-like samples with material columns of diameter of 1 and 1.3 mm, and wall thickness of the sample tubes, δ∈<0.1 mm, >0.5 mm. The increased effect of the Dewar arises because the active volume of the quartz Dewar tube walls is always much more larger than the active volume of the sample tube wall. In the case of the double TE₁₀₄ rectangular cavity, the insertion of the quartz Dewar: (i) into the same cavity, in which the sample is present, caused a direct “lens effect”, with ca. 1.8-fold increase of the EPR signal intensity; however, (ii) into the complementary cavity, in which the sample is absent, caused an indirect “lens effect”, with ca. 0.6-fold decrease of the EPR signal intensity. With the Dewar and sample in one cavity and a large empty sample tube in the complementary cavity, a concurrent (positive or negative) “lens effect” can be observed. Thus, the possible increase/decrease of the EPR signal intensity depends on the volume ratio of the quartz Dewar tube walls and large sample tube wall inserted into the double TE₁₀₄ rectangular cavity. Each of the above phenomena may be a significant source error in quantitative EPR spectrometry unless the samples to be compared in the quantitative EPR analysis are contained in sample tubes having the same wall thickness and each EPR spectra should be recorded inside an identical quartz Dewar.     

Simultaneous determination of copper and iron in automotive gasoline by X-ray fluorescence after pre-concentration on cellulose paper

This paper proposes an alternative analytical method using energy dispersive X-ray fluorescence (EDXRF) to determine Fe and Cu in gasoline samples. In the proposed procedure, samples were distilled and the distillation residues were spotted on cellulose paper disk to form a uniform thin film and to produce a homogeneous and reproducible interface to the XRF instrument. The disks were dried at 60 °C for 20 min and copper and iron were determined directly in the solid phase at 6.40 and 8.04 keV, respectively. The calibration curves showed linear response in the 20-800 μg L⁻¹ concentration range of each metal. The precisions (repeatability) calculated from 15 consecutive measurements and defined as the coefficient of variation of solutions containing 100 μg L⁻¹ of Fe and Cu were 7.8 and 8.1%, respectively. The limits of detection (LOD), defined as the analyte concentration that gives a response equivalent to three times the standard deviation of the blank (n = 10), were found to be 10 and 15 μg L⁻¹ for Fe and Cu, respectively. The proposed method was applied to copper and iron determination in gasoline samples collected from different gas stations.     

Field measurement of nitrate in marine and estuarine waters with a flow analysis system utilizing on-line zinc reduction

A sensitive reagent-injection flow analysis method for the spectrophotometric determination of nitrate in marine, estuarine and fresh water samples is described. The method is based on the reduction of nitrate in a micro column containing zinc granules at pH 6.5. The nitrite formed is reacted with sulfanilamide and N-(1-naphthyl)ethylene diamine (Griess reagent), and the resulting azo compound is quantified spectrophotometrically at 520 nm. Water samples in the range of 3-700 μg L⁻¹ NO₃⁻-N can be processed with a throughput of up to 40 samples per hour, a detection limit of 1.3 μg L⁻¹ and reproducibility of 1.2% RSD (50 μg L⁻¹ NO₃⁻-N, n = 10). The proposed method was successfully applied for the determination of nitrate in estuarine waters and the reliability was assessed by the analyses of certified reference materials and recovery experiments. The method is suitable for waters with a wide range of salinities, and was successfully used for more than 3200 underway nitrate measurements aboard SV Pelican1 in the “Two Bays” cruise in January 2010.     

Sorption characteristics and chromatographic separation of gold (I and III) from silver and base metal ions using polyurethane foams

The influence of different parameters on the sorption profiles of trace and ultra traces of gold (I) species from the aqueous cyanide media onto the solid sorbents ion exchange polyurethane foams (IEPUFs) and commercial unloaded polyurethane foams (PUFs) based polyether type has been investigated. The retention of gold (I) species onto the investigated solid sorbents followed a first-order rate equation with an overall rate constant k in the range 2.2-2.8 ± 0.2 s⁻¹. The sorption data of gold (I) followed Freundlich and Langmuir isotherm models. Thus, the a dual-mode of sorption mechanism involving absorption related to “weak base anion exchanger” and an added component for “surface adsorption” seems the most likely proposed dual mechanism for retention profile of gold (I) by the IEPUFs and PUFs solid sorbents. The capacity of the IEPUFs and PUFs towards gold (I) sorption calculated from the sorption isotherms was found to be 11.21 ± 1.8 and 5.29 ± 0.9 mg g⁻¹, respectively. The chromatographic separation of the spiked inorganic gold (I) from de ionized water at concentrations 5-15 μg mL⁻¹ onto the developed IEPUFs and PUFs packed columns at 10 mL min⁻¹ flow rate was successfully achieved. The retained gold (I) species were then recovered quantitatively from the IEPUFs (98.4 ± 2.4%, n = 5) and PUFs (95.4 ± 3.4%, n = 5) packed columns using perchloric acid (60 mL, 1.0 mol L⁻¹) as a proper eluating agent. Thiourea (1.0 mol L⁻¹)-H₂SO₄ (0.1 mol L⁻¹) system was also used as eluating agent for the recovery of gold (I) from IEPUFS (95.4 ± 5.4%, n = 3) and also PUFs (93.4 ± 4.4%, n = 3) packed columns. The performance of the IEPUFs and PUFs packed columns in terms of the height equivalent to the theoretical plates (HETP), number of plates (N), and critical and breakthrough capacities towards gold (I) species were evaluated. The developed IEPUFs packed column was applied successfully for complete retention and recovery (98.5 ± 2.7) of gold (III) species spiked onto tap- and industrial wastewater samples at <10 μg Au mL⁻¹ after reduction to gold (I). The IEPUFs packed column was applied satisfactorily for complete retention and recovery (98.5 ± 2.7) of total inorganic gold (I) and/or gold (III) species spiked to tap- and industrial wastewater samples at <10 μg mL⁻¹ gold. Chromatographic separation of gold (I) from silver (I) and base metal ions (Fe, Ni, Cu and Zn) using IEPUFS packed columns was satisfactorily achieved. The proposed method was applied successfully for the pre-concentration and separation from anodic slime and subsequent FAAS determination of analyte with satisfactory results (recoveries >95%, relative standard deviations <4.0%).     

Magnetic molecular wheels and grids - the need for novel concepts in “zero-dimensional” magnetism

Supramolecular chemistry has allowed the production, by self-assembly, of inorganic complexes with a [N × N] square matrix-like configuration of N² metal centers. Interest in these systems is driven by the potential applications in information technology suggested by such a “two-dimensional” (2D), addressable arrangement of metal ions. From the magnetic perspective [N × N] grids constitute molecular model systems for magnets with extended interactions on a square lattice, which have gained enormous attention in the context of high-temperature superconductors. Numerous [2 × 2] grids as well as a few [3 × 3] grids with magnetic metal ions such as Cu(II), Ni(II), Co(II), Fe(II), and Mn(II) have been created. Magnetic studies unraveled a remarkable variety in their magnetic properties, which will be reviewed in this work with emphasis on the underlying physical concepts. An intriguing issue is the connection of [2 × 2] and [3 × 3] grids with “one-dimensional” (1D) rings, as experimentally realized in the molecular wheels. For a [2 × 2] square of spin centers the distinction between a 2D grid and a 1D ring is semantic, but also a [3 × 3] grid retains 1D character: it is best viewed as an octanuclear ring with an additional ion “doped” into its center. Challenging familiar concepts from conventional magnets, the current picture of elementary excitations in antiferromagnetic rings will be discussed, as a prerequisite to understand the complex [3 × 3] grids.     

Exploiting in situ hydride trapping in tungsten coil atomizer for Se and As determination in biological and water samples

A flow injection hydride manifold was coupled to a 150 W tungsten coil electrothermal atomizer for in situ hydride collection followed by selenium and arsenic determination by ET AAS. Rhodium (200 μg), thermally reduced over the double layer tungsten atomizer, was very efficient at collecting selenium or arsenic hydrides. Prior to analysis, biological samples were digested in closed-vessels microwave digestion system. Prior to the hydride formation, both selenium and arsenic were reduced to valence state (IV) and (III), respectively. The detection limit was 35 ng L⁻¹ for selenium and 110 ng L⁻¹ for arsenic. Sample throughput was 70 h⁻¹ using 30 s of hydride trapping time. Method accuracy was evaluated by analyzing biological-certified reference materials from the National Institute of Standard and Technology (SRM-1577a and SRM-1577b “bovine liver” and RM-8414 “bovine muscle powder”) and from the International Agency for Energy Atomic (A-13 “animal blood”) and one water-certified reference material from the National Institute of Standard and Technology (SRM-1640 trace elements in natural water). By applying a t-test, there was no significant difference at the 95% probability level between the results obtained with the proposed method and those certified values.     

Development and validation of a new analytical method for the determination of 1,4-dichlorobenzene in honey by gas chromatography-isotope dilution mass spectrometry after steam-distillation

A simple, fast, sensitive and robust analytical method using gas chromatography (GC)-isotope dilution mass spectrometry (MS) was developed and validated for the identification and quantification of 1,4-dichlorobenzene (p-DCB) residues in honey samples. The proposed methodology is based on steam-distillation using a Clevenger-type apparatus followed by gas chromatography-mass spectrometry (GC-MS) in the selected ion monitoring (SIM) mode employing the isotopically labeled analogue d₄-1,4-dichlorobenzene (d₄-p-DCB) as internal standard (IS). Validation of the method was performed in two different GC-MS systems, using quadrupole MS (QMS) and ion-trap MS (ITMS) detectors, with no statistically significant differences between two. Recoveries were better than 91% with percent relative standard deviations lower than 12%. The instrumental limits of detection were 1 μg kg⁻¹ in the GC-ITMS system and 0.6 μg kg⁻¹ in the GC-QMS system. The expanded uncertainty was estimated as 17% at the currently accepted “action level” of 10 μg kg⁻¹. The method was applied to the analysis of 310 honey samples in an extensive national monitoring study. A quality control (QC) system applied during the assays has demonstrated a good performance and long-term stability over a period of more than 8 months of continuous operation.     

Ecotoxicity and chemical sediment data classification by the use of self-organising maps

The present paper deals with the presentation in a new interpretation of sediment quality assessment. This original approach studies the relationship between ecotoxicity parameters (acute and chronic toxicity) and chemical components (polluting species like polychlorinated biphenyls (PCBs), pesticides, polycyclic aromatic hydrocarbons (PAH), heavy metals) of lake sediments samples from Turawa Lake, Poland by an application of self-organising maps (SOMs) to the monitoring dataset (59 samples × 44 parameters) in order to obtain visual images of the components distributed at each sampling site when all components are included in the classification and data projection procedure. From the SOMs obtained, it is possible to select groups of similar ecotoxicity (either acute or chronic) and to analyse within each one of them the relationship of the other chemicals to the toxicity determining parameters (EC₅₀ and mortality). Studies have shown, convincingly, that different regions from the Turawa Lake bottom indicate different patterns of ecotoxicity related to various chemical pollutants, such as the “heptachlor-B” pattern, “pesticide and PAH” pattern, “structural” pattern or “PCB congeners” pattern. Thus, an easy way of multivariate analysis of small datasets with ecotoxicity parameters involved becomes possible. Additionally, a distinction between the effects of pollution on acute and chronic toxicity seems reasonable.     

A 4-hydroxy-N′-[(E)-(2-hydroxyphenyl)methylidene]benzohydrazide-based sorbent material for the extraction-HPLC determination of biogenic amines in food samples

A sorbent material based on a newly synthesized hydrazone ligand, 4-hydroxy-N′-[(E)-(2-hydroxyphenyl)methylidene]benzohydrazide was prepared by immobilizing the ligand into a silica sol-gel matrix. The capability of the sorbent material for the extraction of seven biogenic amines (BAs), i.e., tryptamine (TRY), β-phenylethylamine (PEA), putrescine (PUT), cadaverine (CAD), histamine (HIS), tyramine (TYR), and spermidine (SPD) was studied. Under the adopted conditions, the sorbent showed good selectivity towards PUT, CAD, HIS and SPD (% extraction (%E) > 96) while %E for TYR, TRY and PEA were 82.0, 78.9 and 46.4%, respectively. The sorbent could be used up to six extraction cycles for SPD, CAD and PUT and was applied to the determination of food samples (“budu”, ketchup, orange juice, soy sauce) that were spiked with 20 mg L⁻¹ of the BAs. The extracted analytes were derivatized with dansyl chloride before the HPLC determination. With the exception of HIS and TYR in “budu” sample, reasonable recoveries were found for the other analytes in all the tested food samples.     

Glucose biosensor based on the layer-by-layer self-assembling of glucose oxidase and chitosan derivatives on a thiolated gold surface

This work examines in deep the analytical performance of an example of “first-generation” microdevices: capillary electrophoresis microchip (CE) with end-channel electrochemical detection (ED). A hydroquinone and arbutin separation strategically chosen as route involving pharmaceutical-clinical testing, public safety and food control scenes was carried out. The reproducibility of the unpinched electrokinetic protocol was carefully studied and the technical possibility of working indiscriminately and/or sequentially with both simple cross-injectors was also demonstrated using a real sample (R.S.D.'s less than 7%). The robustness of the injection protocol allowed checking the state of the microchip/detector coupling and following the extraction efficiency of the analyte from real sample. Separation variables such as pH, ionic strength and, separation voltage were also carefully assayed and optimized. Analyte screening was performed using borate buffer (pH 9, 60 mM) in less than 180 s in the samples studied improving dramatically the analysis times used for the same analytes on a conventional scale (15 min), with good precision (R.S.D.'s ranging 5-10%), accuracy (recoveries ranging 90-110%) and acceptable resolution (Rs ≥ 1.0).In addition, the excellent analytical performance of the overall analytical method indicated the quality of the whole analytical microsystem and allowed to introduce the definition of robustness for methodologies developed into the “lab-on-a-chip” scene.     

An exonuclease-assisted amplification electrochemical aptasensor of thrombin coupling “signal on/off” strategy

In this work, a dual-signaling electrochemical aptasensor based on exonuclease-catalyzed target recycling was developed for thrombin detection. The proposed aptasensor coupled “signal-on” and “signal-off” strategies. As to the construction of the aptasensor, ferrocene (Fc) labeled thrombin binding aptamer (TBA) could perfectly hybridize with the methylene blue (MB) modified thiolated capture DNA to form double-stranded structure, hence emerged two different electrochemical signals. In the presence of thrombin, TBA could form a G-quadruplex structure with thrombin, leading to the dissociation of TBA from the duplex DNA and capture DNA formed hairpin structure. Exonuclease could selectively digest single-stranded TBA in G-quadruplex structure and released thrombin to realize target recycling. As a consequence, the electrochemical signal of MB enhanced significantly, which realized “signal on” strategy, meanwhile, the deoxidization peak current of Fc decreased distinctly, which realized “signal off” strategy. The employment of exonuclease and superposition of two signals significantly improved the sensitivity of the aptasensor. In this way, an aptasensor with high sensitivity, good stability and selectivity for quantitative detection of thrombin was constructed, which exhibited a good linear range from 5 pM to 50 nM with a detection limit of 0.9 pM (defined as S/N = 3). In addition, this design strategy could be applied to the detection of other proteins and small molecules.