Forgot your password?
New user?
New Window Opens on the Secret Life of Microbes: Scientists Develop First Microbial Profiles of Ecosystems
CAS announces the release of SciFinder Scholar for Mac OS X
Press Releases
Press Releases
| Check out our New Publishers' Select for Free Articles |
Analytical and Bioanalytical Chemistry (v.379, #7-8)
A miniaturized heterogeneous fluorescence immunoassay on gold-coated nano-titer plates by Michael Seidel; Daniela M. Dankbar; Günter Gauglitz (pp. 904-912).
A miniaturized heterogeneous fluorescence immunoassay utilizing radiationless energy transfer to gold surfaces for fluorescence quenching is described. The phase-separation fluorescence immunoassay (PSFIA), a competitive heterogeneous assay, is carried out in the nanowells of a gold-coated nano-titer plate (NTP). Small analytes such as atrazine and histamine can be detected in nanoliter volumes with low limits of detection, maintaining a high degree of parallelization and miniaturization. The assay is characterized and optimized with respect to gold-layer thickness, surface concentration of immobilized analyte derivative, and antibody concentration. Various immobilization strategies are discussed.
Keywords: Fluorescence immunoassay; Miniaturization; Parallelization; Gold-coated surface; Radiationless energy transfer; Fluorescence resonance energy transfer (FRET)
Application of luminescent nanocrystals as labels for biological molecules by Jürgen Riegler; Thomas Nann (pp. 913-919).
Luminescent semiconductor nanocrystals, so called “quantum dots” (QD), have attracted increasing interest for bioanalytical labeling applications in recent years. This review describes the major optical and (bio)chemical features of this class of label, compared with organic dyes. Different conjugation methods are also discussed and the most important recent applications are presented. An overview over the current state-of-the-art is given, as also is an outlook on possibilities and limitations.
Keywords: Quantum dots; Luminescent nanocrystals; Fluorescence; Bioanalysis; Fluorescent immunoassays
A unified view of propagating and localized surface plasmon resonance biosensors by Amanda J. Haes; Richard P. Van Duyne (pp. 920-930).
The intense colors of noble metal nanoparticles have inspired artists and fascinated scientists for hundreds of years. In this review, we describe refractive index sensing platforms based on the tunability of the localized surface plasmon resonance (LSPR) of arrays of silver nanoparticles and of single nanoparticles. Specifically, the color associated with single nanoparticles and surface-confined nanoparticle arrays will be shown to be tunable and useful as platforms for chemical and biological sensing. Finally, the LSPR nanosensor will be compared to traditional, flat surface, propagating surface plasmon resonance sensors.
Keywords: Localized surface plasmon resonance; Nanosensor; Single nanoparticle; Spectroscopy; Biosensing
Optical fiber-based biosensors by David J. Monk; David R. Walt (pp. 931-945).
This review outlines optical fiber-based biosensor research from January 2001 through September 2003 and was written to complement the previous review in this journal by Marazuela and Moreno-Bondi. Optical fiber-based biosensors combine the use of a biological recognition element with an optical fiber or optical fiber bundle. They are classified by the nature of the biological recognition element used for sensing: enzyme, antibody/antigen (immunoassay), nucleic acid, whole cell, and biomimetic, and may be used for a variety of analytes ranging from metals and chemicals to physiological materials.
Keywords: Fiber; Optic; Optical; Biosensor; Sensor
Cantilever-based biosensors by Christiane Ziegler (pp. 946-959).
This review provides a general introduction into the theory of cantilever sensors, including practical design concepts, examples for liquid-phase sensing with particular emphasis on biological applications, and a discussion of future prospects.
Keywords: Cantilever; Biosensor; Micromechanical sensor
Biomolecular and amphiphilic films probed by surface sensitive X-ray and neutron scattering by Tim Salditt; Guillaume Brotons (pp. 960-973).
In this review article we discuss the thin film analytical techniques of interface sensitive X-ray and neutron scattering applied to aligned stacks of amphiphilic bilayers, in particular phospholipid membranes in the fluid L α phase. We briefly discuss how the structure, composition, fluctuations and interactions in lipid or synthetic membranes can be studied by modern surface sensitive scattering techniques, using X-rays or neutrons as a probe. These techniques offer an in-situ approach to study lipid bilayer systems in different environments over length scales extending from micrometer to nanometer, both with and without additional membrane-active molecules such as amphiphilic peptides or membrane proteins.
Keywords: Lipid membrane; X-ray analysis; Thin biomolecular films
Double-chip protein arrays: force-based multiplex sandwich immunoassays with increased specificity by Kerstin Blank; Andreas Lankenau; Thao Mai; Susanne Schiffmann; Ilka Gilbert; Siegfried Hirler; Christian Albrecht; Martin Benoit; Hermann E. Gaub; Hauke Clausen-Schaumann (pp. 974-981).
Protein assays provide direct access to biologically and pharmacologically relevant information. To obtain a maximum of information from the very smallest amounts of complex biological samples, highly multiplexed protein assays are needed. However, at present, cross-reactions of binding reagents restrict the use of such assays to selected cases and severely limit the potential for up-scaling the technology. Here we describe a double-chip format, which can effectively overcome this specificity problem for sandwich immunoassays. This format consists of a capture array and a reference array with fluorescent labeled detection antibodies coupled to the reference array via DNA duplexes. This format allows for the local application of the labeled detection antibodies onto their corresponding specific spots on the capture array. Here we show that this double-chip format allows for the use of cross-reactive antibodies without generating false positive signals, and an assay for the parallel detection of seven different cytokines was set up. Even without further optimization, the dynamic range and the limit of detection for interleukin 8 were found to be comparable to those obtained with other types of multiplexed sandwich immunoassays.
Keywords: Sandwich immunoassay; Protein array; Cytokine; Specificity; Cross-reactivity; Multi-analyte
Acoustic manipulation of small droplets by Achim Wixforth; Christoph Strobl; Ch. Gauer; A. Toegl; J. Scriba; Z. v. Guttenberg (pp. 982-991).
Surface acoustic waves are used to actuate and process smallest amounts of fluids on the planar surface of a piezoelectric chip. Chemical modification of the chip surface is employed to create virtual wells and tubes to confine the liquids. Lithographically modulated wetting properties of the surface define a fluidic network, in analogy to the wiring of an electronic circuit. Acoustic radiation pressure exerted by the surface wave leads to internal streaming in the fluid and eventually to actuation of small droplets along predetermined trajectories. This way, in analogy to microelectronic circuitry, programmable biochips for a variety of assays on a chip have been realized.
Keywords: Biochip; Surface acoustic waves; Droplet; Microarray; Hybridization; PCR
Identification of the regulatory proteins in human pancreatic cancers treated with Trichostatin A by 2D-PAGE maps and multivariate statistical analysis by Emilio Marengo; Elisa Robotti; Daniela Cecconi; Mahmoud Hamdan; Aldo Scarpa; Pier Giorgio Righetti (pp. 992-1003).
In this paper, principal component analysis (PCA) is applied to a spot quantity dataset comprising 435 spots detected in 18 samples belonging to two different cell lines (Paca44 and T3M4) of control (untreated) and drug-treated pancreatic ductal carcinoma cells. The aim of the study was the identification of the differences occurring between the proteomic patterns of the two investigated cell lines and the evaluation of the effect of the drug Trichostatin A on the protein content of the cells. PCA turned out to be a successful tool for the identification of the classes of samples present in the dataset. Moreover, the loadings analysis allowed the identification of the differentially expressed spots, which characterise each group of samples. The treatment of both the cell lines with Trichostatin A therefore showed an appreciable effect on the proteomic pattern of the treated samples. Identification of some of the most relevant spots was also performed by mass spectrometry.
Keywords: PCA; Chemometrics; Human pancreatic tumour; Trichostatin A; Protein identification
Ultra-sensitive fully automated immunoassay for detection of propanil in aqueous samples: steps of progress toward sub-nanogram per liter detection by Jens Tschmelak; Guenther Proll; Guenter Gauglitz (pp. 1004-1012).
The widely-used pesticide propanil is a selective post-emergent general-use acetanilide herbicide registered for control of broadleaf and grass weeds in rice, small grain, and turf. Because broad application and quite heavy use of this herbicide lead to contaminated sites and, consequently, contaminated water, immunoanalytical methods with very low limits of detection (LOD) and low limits of quantification (LOQ) are becoming increasingly important for environmental analysis and, especially, for monitoring drinking-water quality. Environmental monitoring of pesticides, hormones, endocrine-disrupting chemicals, and antibiotics in aqueous samples (e.g. surface, ground, waste, or drinking water) with quite difficult matrices places large demands on chemical analysis. Biosensors have suitable characteristics such as efficiency in enabling very fast, sensitive, and cost-effective detection. Here we describe the steps of progress toward sub-nanogram per liter detection of propanil with a fully automated immunoassay. In contrast with common analytical methods such as GC–MS or HPLC–MS the biosensor used requires no sample pre-treatment and pre-concentration. The basis of our sensitive assay is an antibody with a high affinity constant toward propanil. During the optimization process, we compared different surface modifications (four different immobilized derivatives) and reduced the amount of antibody per sample. In fact, optimization of the assay resulted in an LOD of 0.6 ng L−1 and an LOQ of 4.5 ng L−1 without any sample pre-treatment and without pre-concentration. These results for propanil with the RIANA instrument, and its improved sensitivity for detection of a single pesticide at the low nanogram per liter range, show that biosensors can compete with common analytical methods in the field of water analysis.
Keywords: River analyzer (RIANA) and automated water analyzer computer-supported system (AWACSS); Environmental analysis; Immunoassay; Propanil; Biosensor; Analytical data processing
Liquid chromatography/Fourier transform ion cyclotron resonance mass spectrometry (LC-FTICR MS): an early overview by Wolfgang Schrader; Heinz-Werner Klein (pp. 1013-1024).
Fourier-transform ion cyclotron resonance mass spectrometry has developed into one of the most powerful analytical techniques. This unique technique enables acquisition of high-resolution mass spectra with high accuracy, which in turn enables determination of the elemental composition of the analyzed compounds. Coupling with liquid chromatography affords a separation technique with a high-resolution “detector” which can be used to investigate very complex matrices. In this review some important instrumental developments are described and applications are presented; these show the advantages and disadvantages of this combination.
Keywords: Liquid chromatography; Fourier-transform ion cyclotron resonance mass spectrometry; LC–FTICR; Proteomics; High-resolution mass spectrometry
Silica-nanoparticle-based interface for the enhanced immobilization and sequence-specific detection of DNA by D. Zhang; Y. Chen; H. -Y. Chen; X. H. Xia (pp. 1025-1030).
A biocompatible and uniform interface based on silica nanoparticles derivatized with amino groups has been constructed for the effective immobilization and sensitive sequence-specific detection of calf thymus DNA. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) results showed that a monolayer of silica nanoparticles can be formed on a gold electrode under our experimental conditions using cysteine self-assembly monolayer as binder medium. Electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy (XPS) verified the successful immobilization of DNA on silica-nanoparticle-modified gold electrodes. Quantitative results demonstrated that enhanced immobilization of single-strand DNA (ss-DNA) up to 1.6×10−8 mol cm−2 could be achieved owing to the larger surface area and the special properties of silica nanoparticles. In addition, hybridization experiments demonstrated that the immobilized ss-DNA on silica nanoparticles could specifically interact with complementary DNA in solutions.
Keywords: Silica nanoparticles; DNA immobilization; Sequence-specific electrochemical detection
Structural characterisation of some fatty acids from the brain as biomarkers of BSE risk material by Wolfgang Biedermann; Ernst Lücker; Jürgen Pörschmann; Sandra Lachhab; Uwe Truyen; Andreas Hensel (pp. 1031-1038).
Identification of bovine and ovine tissue from the central nervous system (CNS: brain and spinal cord) in meat products is possible by using certain CNS fatty acids as biomarkers in GC–MS analysis. Furthermore, the relationship between the isomers of the tetracosenic acid (C24:1) is important for differentiation of the species and age of the CNS in view of the legal definition of specified risk material (SRM). This has so far been referred to as the “cis/trans ratio of the isomers of nervonic acid”; however, structural analysis was not performed. Here we present results from GC–MS structural analysis by retention time and DMDS adduct profiling of the even numbered monoenoic fatty acids from C18:1 to C26:1. Retention times and mass spectra of the FAME standards indicated that the so far designated trans-nervonic acid has a different isomeric structure in the tetracosenic acid from brain-sample extracts. By performing GC–MS analysis of DMDS adducts we have shown that this isomer was actually cis-17-tetracosenic acid in all species so far tested, not trans-15-tetracosenic acid (trans-nervonic acid). The tetracosenic acid isomer ratio proved to be species-specific in accordance with previous results. Thus, instead of the ratio of cis/trans isomers of nervonic acid, the ratio of ω9/ω7-tetracosenic acid (15c-C24:1/17c-C24:1) will have to be used as a correct reference in future publications. Although trans isomers were not detectable in sheep and cattle brain, porcine brain contained, in addition to cis-17-tetracosenic acid, small amounts of the trans isomers of the C18:1, C20:1, C24:1, and C26:1 fatty acids, in decreasing quantities. In future, this might be useful as another means of differentiation between porcine CNS (non-SRM) and ovine or bovine CNS (SRM). Extensive follow-up studies must be performed to elucidate the extent to which this GC–MS approach will facilitate the detection of CNS according to the legal SRM definition.
Keywords: BSE; SRM; CNS; GC–MS; Fatty acids; Nervonic acid; Structural analysis
Enantiomer discrimination by mass spectrometry: noncovalent interactions of an N-derivatized dipeptide with various cinchona alkaloid derivatives and comparison with enantioselective liquid-phase separations by Christoph Czerwenka; Norbert M. Maier; Wolfgang Lindner (pp. 1039-1044).
The enantiomer discrimination properties of cinchona alkaloid derived chiral selectors (CSs) towards a dipeptide analyte are examined by electrospray ionization mass spectrometry. The complexes formed between the CSs and the analyte enantiomers owing to various noncovalent interactions are analyzed and the magnitudes of enantiomer discrimination are determined from the complexes’ mass spectrometric intensities. The influence of different structural features of the CSs on enantioselectivity is discussed. The enantiomer discrimination results obtained by mass spectrometry are compared with those from related liquid chromatography enantiomer separations. A certain coherence between the chromatographic and mass spectrometric enantioselectivities could be established and the enantiomer discrimination patterns, i.e., the relative binding strengths, were identical for the two techniques. Thus, the use of mass spectrometry as a screening tool in the development of new CSs for chromatographic applications seems feasible.
Keywords: Mass spectrometry; Enantiomer discrimination; Chiral selector; Peptide; Enantiomer separation; Liquid chromatography
Flavonoid binding to a multi-drug-resistance transporter protein: an STD-NMR study by Ludwig Nissler; Rolf Gebhardt; Stefan Berger (pp. 1045-1049).
Flavonoids are well known to inhibit the function of the multi-drug-resistance (mdr) transporter by interacting with their ATP binding domains. The precise orientation of these molecules inside the ATP binding pocket is still unclear. We applied the saturation transfer difference (STD) NMR technique to investigate the binding of the flavonoid luteolin and its 7-O-β-D-glycopyranoside to the recombinant nucleotide binding domain (NBD2) of mouse-mdr. First, this NMR technique confirmed binding of both ligands to NBD2, as was determined from tryptophan fluorescence-quenching experiments. Further, the results suggest binding of both luteolin and its 7-O-β-D-glycopyranoside by their polar groups at positions 4, 5, and 3′ to the protein.
Keywords: ATP binding pocket; Flavonoids; Multi-drug-resistance protein; Protein–ligand interaction; STD-NMR technique
Determination of the MRI contrast agent Gd-DTPA by SEC–ICP–MS by Valeria Loreti; Jörg Bettmer (pp. 1050-1054).
The simultaneous determination of Gd3+ and Gd-DTPA (DTPA: diethylenetriamino-pentaacetic acid), often used as contrast agent, is described. The proposed approach combines size-exclusion chromatography (SEC) and inductively coupled plasma–mass spectrometry (ICP–MS) for element-selective detection in order to determine also high-molecular Gd-complexes if present. This method was applied to the analysis of urine samples of a patient to whom Gd-DTPA was intravenously administered. The results showed that no conversion or adsorption of Gd-DTPA could be observed in any sample, even free Gd3+ could not be detected. Urine excretion behaviour was monitored and it was proved that Gd-DTPA was almost completely (>99%) excreted by urination within one day. Traces of Gd-DTPA could be measured in hair samples, but extraction with tetramethylammonium hydroxide (TMAH) resulted in degradation of Gd-DTPA.
Keywords: Gd-DTPA; Gd speciation; SEC; ICP–MS
Eliminating absorbing interference using the H-point standard addition method: case of Griess assay in the presence of interferent heme enzymes such as NOS by Perera N. Indika; Mekki Bayachou (pp. 1055-1061).
Standard calibration methods used to determine trace analytes usually yield significant deviations from the actual analyte value in the presence of interferents in the assay media. These deviations become of particular concern when the concentration of the analyte is low, and when the results are used to draw mechanistic or kinetic conclusions, for instance in enzyme structure-function studies. In these circumstances, the H-point standard addition method (HPSAM) provides superior precision and accuracy. This method is developed here for the case of the spectrophotometric Griess assay used to determine nitrite in various enzymology investigations, such as nitrite determination in studies of nitrite reductases (NiR), or when determining nitrite as a breakdown product of nitric oxide synthesized by NOS enzymes. The results obtained by HPSAM are contrasted with those of the traditional calibration method.
Keywords: Nitrite; Determination; NOS; Enzymes; Griess; Assay
Poly(dimethylsiloxane) microchip capillary electrophoresis with electrochemical detection for rapid measurement of acetaminophen and its hydrolysate by F. Y. He; A. L. Liu; X. H. Xia (pp. 1062-1067).
Poly(dimethylsiloxane) microchip capillary electrophoresis with amperometric detection has been used for rapid separation and determination of acetaminophen and its hydrolysate, i.e. p-aminophenol. A Pt ultramicroelectrode with a diameter of 10 μm positioned at the outlet of the separation channel was used as a working electrode for amperometric detection. Factors influencing separation and detection were investigated and optimized. Results show that acetaminophen and p-aminophenol can be well separated within 35 s with RSD<1% for migration time and <7% for detection current for both analytes. Detection limits for both analytes are estimated to be 5.0 μmol L−1 (approximately 0.1 fmol) at S/N=3. This method has been successfully applied to the detection of traces of p-aminophenol in paracetamol tablets.
Keywords: Poly(dimethylsiloxane); Microchip capillary electrophoresis; Electrochemical detection; Acetaminophen; p-Aminophenol; Ultramicroelectrode; Paracetamol tablet
Coupling gravitational and flow field-flow fractionation, and size-distribution analysis of whole yeast cells by Ramsés Sanz; Lluís Puignou; Maria Teresa Galceran; Pierluigi Reschiglian; Andrea Zattoni; Dora Melucci (pp. 1068-1075).
This work continues the project on field-flow fractionation characterisation of whole wine-making yeast cells reported in previous papers. When yeast cells are fractionated by gravitational field-flow fractionation and cell sizing of the collected fractions is achieved by the electrosensing zone technique (Coulter counter), it is shown that yeast cell retention depends on differences between physical indexes of yeast cells other than size. Scanning electron microscopy on collected fractions actually shows co-elution of yeast cells of different size and shape. Otherwise, the observed agreement between the particle size distribution analysis obtained by means of the Coulter counter and by flow field-flow fractionation, which employs a second mobile phase flow as applied field instead of Earth’s gravity, indicates that yeast cell density can play a major role in the gravitational field-flow fractionation retention mechanism of yeast cells, in which flow field-flow fractionation retention is independent of particle density. Flow field-flow fractionation is then coupled off-line to gravitational field-flow fractionation for more accurate characterisation of the doubly-fractionated cells. Coupling gravitational and flow field-flow fractionation eventually furnishes more information on the multipolydispersity indexes of yeast cells, in particular on their shape and density polydispersity.
Keywords: Yeast; Saccharomyces; Gravitational field-flow fractionation; Flow field-flow fractionation; Coulter counter; Particle-size-distribution analysis
Direct determination of trace refractory elements in human serum by ETV–ICP–MS with in-situ matrix removal by Shengqing Li; Bin Hu; Zucheng Jiang; Rui Chen (pp. 1076-1082).
A method for in-situ removal of matrix is proposed for direct determination of trace refractory elements in human serum by ETV–ICP–MS with the use of poly(tetrafluoroethylene) (PTFE) as fluorinating reagent. Attention has been paid to investigating the vaporization behavior both of refractory elements of interest and of matrix elements (Na, K, Ca, Mg, Cl, S, and P) in a graphite furnace with the PTFE modifier present or not. It was shown that potential interferences from the organic and inorganic matrices in the serum sample could be eliminated or reduced to a negligible level by appropriate dilution of the serum and deliberate optimization of the ETV temperature program. The proposed method has been applied to the direct simultaneous determination of V, Cr, Mo, Ba, La, Ce, and W in human serum. The limits of detection for fivefold diluted serum were 0.18 (V), 0.229 (Cr), 0.050 (Mo), 0.328 (Ba), 0.031 (La), 0.038 (Ce), and 0.019 ng mL−1 (W), respectively, and the relative standard deviations of the method were in the range 4–15% (2 ng mL−1 in serum, n=3).
Keywords: ETV–ICP–MS; Refractory elements; Serum; In-situ matrix removal; Poly(tetrafluoroethylene)
Separation of traces of heavy metals from an iron matrix by use of an emulsion liquid membrane by Tomohiro Kageyama; Hiroaki Matsumiya; Masataka Hiraide (pp. 1083-1087).
An emulsion liquid membrane method has been developed for separating traces of heavy metals from an iron matrix. A 1.0-mL volume of aqueous iron(III) solution (pH 2.0) was emulsified with a mixture of 0.6 mL toluene, 2.4 mL n -heptane, and 80 mg sorbitan monooleate (Span-80). The resulting water-in-oil type emulsion was gradually injected into 25 mL of 1.5 mol L−1 hydrochloric acid solution containing 30 mmol L−1 8-quinolinol and 1.0 mol L−1 of ammonium sulfate and was dispersed as numerous tiny globules by stirring for 40 min. More than 90% of the iron(III) diffused through the oil layer to the external hydrochloric acid solution with the aid of complexation with 8-quinolinol, whereas trace heavy metals, e.g. Cr(III), Mn(II), Co(II), Ni(II), Cu(II), and Pb(II), remained quantitatively in the internal aqueous phase. After collecting the dispersed emulsion globules, they were demulsified and trace metals in the segregated aqueous phase were determined by graphite-furnace atomic absorption spectrometry. Owing to sufficient removal of the iron matrix trace metal impurities in high-purity iron were successfully determined without interference, as was confirmed by analysis of certified reference materials.
Keywords: Emulsion; Matrix-removal; High-purity iron; Trace impurities; Atomic absorption spectrometry
Specific polyclonal-based immunoassays for sulfathiazole by Nuria Pastor-Navarro; Cristina García-Bover; Ángel Maquieira; Rosa Puchades (pp. 1088-1099).
A highly sensitive and specific enzyme-linked immunosorbent assay has been developed for detection of sulfathiazole (STZ, 4-amino-N-thiazol-2-yl-benzenesulfonamide). A set of haptens was synthesized in order to produce polyclonal antibodies against sulfonamides. Two ELISA formats (antibody-coated and conjugate-coated) were also investigated using all the serum/coating conjugate combinations that showed specific recognition. The developed ELISA succeeded in detection of STZ at concentrations as low as 0.03 ng mL−1 over a measurable range of 0.12–6.71 ng mL−1. Selectivity studies have demonstrated that other sulfonamides do not interfere significantly (<10%) with analysis of STZ by this immunochemical technique. Analysis of spiked bee honey samples by the developed ELISA method showed recoveries were good. The selectivity and sensitivity (IC50=1.6 ng mL−1) make it a suitable screening method for determination of low levels of STZ in food samples.
Keywords: Antimicrobials; Sulfonamides; Sulfathiazole; ELISA; Honey
Determination of pyrimethanil and kresoxim-methyl in soils by headspace solid-phase microextraction and gas chromatography-mass spectrometry by Alberto Navalón; Avismelsi Prieto; Lilia Araujo; José Luis Vílchez (pp. 1100-1105).
A method using headspace solid-phase microextraction (HS-SPME) then gas chromatography–mass spectrometry with selected ion monitoring (GC–MS, SIM) has been developed for determination of trace amounts of the fungicides pyrimethanil and kresoxim-methyl in soil and humic materials. Both fungicides were extracted on to a fused-silica fibre coated with 85 μm polyacrylate (PA). Response-surface methodology was used to optimise the experimental conditions. For soil samples the linear dynamic range of application was 0.004–1.000 μg g−1 for pyrimethanil and 0.013–1.000 μg g−1 for kresoxim-methyl. The detection limits were 0.001 μg g−1 and 0.004 μg g−1 for pyrimethanil and kresoxim-methyl, respectively. HP-SPME–GC–MS analysis was highly reproducible—relative standard deviations (RSD) were between 6.7 and 12.2%. The method was validated by analysis of spiked matrix samples and used to investigate the presence of pyrimethanil and kresoxim-methyl above the detection limits in soil and humic materials.
Keywords: Pyrimethanil; Kresoxim-methyl; Headspace solid-phase microextraction; Gas chromatography–mass spectrometry; Soil analysis
Ultrasound-assisted extraction for the analysis of phenolic compounds in strawberries by M. C. Herrera; M. D. Luque de Castro (pp. 1106-1112).
A semiautomatic method based on application of ultrasounds has been developed to leach and hydrolyse phenolic compounds, such as naringin, rutin, naringenin, ellagic acid, quercetin and kaempferol, from strawberries. Two grams of lyophilized sample was placed into a sample cell and 5 mL of acetone containing hydrochloric acid was added. The cell was immersed in a water bath and sonicated for 30 s (duty cycle 0.8 s, output amplitude 50% of the nominal amplitude of the converter, applied power 100 W and with the probe placed 2 cm from the top surface of the extraction cell) for three times: each time 5 mL extractant displaced the previous extract. When the extraction was completed, the combined extracts were evaporated for 10 min, diluted to 10 mL with water adjusted to pH 8, and transferred to a cleanup–preconcentration manifold; here the analytes were retained in two in-series minicolumns packed with HR-P sorbent and then eluted with 4 mL methanol, and injected for individual separation–quantitation into a chromatograph–photodiode array detector assembly. Optimisation of the extraction was carried out using samples spiked with 4 mg kg−1 of each analyte. Calibration curves using the standard addition in red strawberries typically gave linear dynamic ranges of 4–40 mg L−1 for all analytes, except for ellagic acid (40–400 mg L−1). The r 2 values exceeded 0.98 in all cases.
Keywords: Ultrasound-assisted extraction; Flavonoids; Flavonols
Measurement of total selenium and selenium(IV) in seawater by stripping chronopotentiometry by Ricardo D. Riso; Matthieu Waeles; Sébastien Garbarino; Pierre Le Corre (pp. 1113-1119).
We developed a stripping chronopotentiometric method (constant current stripping analysis, CCSA) with a mercury film electrode for selenium quantification in seawater. A sensitivity and detection limit of 222 ms ng−1 l and 4 ng l−1 (50 pM), respectively, were accomplished for a 3-min electrolysis time. Compared to the other chronopotentiometric methods available for a single selenium measurement only in natural waters, our procedure exhibits a ten times better sensitivity. It, therefore, allows one to reach the current concentration thresholds found in coastal and oceanic waters (30–200 ng l−1). Moreover, a simple change in operating conditions enables one to also quantify Se(IV), a toxic dissolved species. With respect to the other electrochemical methods of current use, our procedure is beneficial because of its ease-of-use: it needs neither degassing step, nor catalyser.
Keywords: Stripping chronopotentiometry; Selenium; Selenium(IV); Seawater
Improvement of sensitivity in the determination of organochlorine pesticides using a PSS injector with GC-ECD by E. Concha-Graña; M. I. Turnes-Carou; S. Muniategui-Lorenzo; P. López-Mahía; E. Fernández-Fernández; D. Prada-Rodríguez (pp. 1120-1126).
This paper describes the optimisation of a PSS injector in a gas chromatograph with a programmed pneumatic control (PPC) for the determination of 21 organochlorine pesticides. The injection of high volumes of sample (20 μl) improves the detection limits and allows a reduction in the amount of sample processed. The injection conditions were selected by a Plackett–Burman design followed by a central composite design. The LODs obtained in the optimum conditions were compared with those obtained with splitless/ECD. Finally, the method was successfully applied to the analysis of a leachate and vegetable samples.
Keywords: Organochlorine pesticides; PSS; Large volume injection; Programmed pneumatic control; Experimental designs
Superheated water extraction, steam distillation and Soxhlet extraction of essential oils of Origanum onites by Mustafa Z. Ozel; Hilal Kaymaz (pp. 1127-1133).
Superheated water extraction (SWE) at various temperatures (100, 125, 150 and 175°C), steam distillation, and Soxhlet extraction were compared in the extraction of essential oils from two samples of the plant Origanum onites, one cultivated, the other wild. C18 solid-phase extraction was used to elute the essential oils from the SWE aqueous extract. The compositions of the extracted essential oils obtained from all three methods were then characterized by comprehensive GC×GC/time-of-flight mass spectrometry (TOF/MS). The highest essential oil yields were obtained by using SWE at 150°C with a flow rate of 2 mL min−1 and a pressure of 60 bar for 30 min: these were 3.76 and 4.11% for wild and cultivated O. onites samples, respectively, expressed as a percentage of 100 g of dry (leaf) matter. The yields obtained using SWE at 150°C were slightly higher than those from conventional methods. Steam distillation was performed for 3 h, and Soxhlet extraction was completed in 12 h. The major compounds found were borneol, terpinen-4-ol and carvacrol.
Keywords: Superheated water extraction; Steam distillation; Soxhlet extraction; Gas chromatography–mass spectrometry