Analytica Chimica Acta (v.677, #1)
Editorial Board (iii).
ExTech 2009 SI by Doug Raynie (1-2).
Fundamentals and applications of needle trap devices by Heather L. Lord; Weiqiang Zhan; Janusz Pawliszyn (3-18).
The needle trap device (NTD) is an extraction trap that contains a sorbent inside a small needle, through which fluid can be actively drawn into and out of by a gas-tight syringe or pump, or analytes can be introduced passively to the trap by diffusion. The needle trap (NT) is a potentially solventless sampling technique/sample preparation and introduction device. Both fluid-borne analytes and particles can be trapped inside the needle and then adsorbed analytes are desorbed in an inlet of analytical instrument and introduced for identification and quantification. The fluid may be either gaseous or liquid. The objectives of this critical review are to summarize the theory of the sampling process for both active and passive time-average extraction modes in addition to outlining the evolution of the technology and main applications.
Keywords: Needle trap device; Sample preparation; Solid phase extraction; Solid phase microextraction; Liquid chromatography; Gas chromatography;
Novel pressurized solvent extraction vessels for the analysis of polychlorinated biphenyl congeners in avian whole blood by S.D. Haskins; D.G. Kelly; R.D. Weir (19-23).
Persistent organic pollutants remain a serious threat to many food-chain systems. New pollutants continue to emerge. The present study has created novel extraction vessels which are compatible with readily available commercial instrumentation to validate the analysis of one class of persistent organic pollutants, polychlorinated biphenyls (PCBs), in avian blood. The volumes used can be reasonably sampled without sacrificing individuals, or comprising breeding or migratorial success. The procedure consists of the pressurized solvent extraction (PSE) of analytes in a novel PSE extraction vessel. The new extraction cell contains a 38-cm long, coiled, re-packable, in situ clean-up column. Lipid elimination, using Florisil, occurs within the coiled region of the extraction vessel, eliminating the requirement for post extraction clean-up. For development, 0.2 g samples of chicken whole blood have been used. Extract volumes are reduced from (30 to 10) cm3, compared to unmodified systems. The new PSE vessel with its integrated clean-up method showed satisfactory performance for the analysis of ten environmentally relevant PCB congeners in chicken whole blood samples with recoveries in the range of (70–130)%. Detection limits using gas chromatography coupled with large volume injection ion-trap mass spectrometry (GC–LVI–ITMS–MS) were in the range of (0.05–0.5) ng g−1. The relative standard deviations for all congeners investigated were better than 5%. This is the first PSE validation to have been conducted on unaltered whole blood samples.
Keywords: Polychlorinated biphenyls; Pressurized solvent extraction; Avian blood; Large volume injection gas chromatography; Ion-trap mass spectrometry; Tandem mass spectrometry;
Determination of cyanide exposure by gas chromatography–mass spectrometry analysis of cyanide-exposed plasma proteins by Stephanie L. Youso; Gary A. Rockwood; John P. Lee; Brian A. Logue (24-28).
Exposure to cyanide can occur in a variety of ways, including exposure to smoke from cigarettes or fires, accidental exposure during industrial processes, and exposure from the use of cyanide as a poison or chemical warfare agent. Confirmation of cyanide exposure is difficult because, in vivo, cyanide quickly breaks down by a number of pathways, including the formation of both free and protein-bound thiocyanate. A simple method was developed to confirm cyanide exposure by extraction of protein-bound thiocyanate moieties from cyanide-exposed plasma proteins. Thiocyanate was successfully extracted and subsequently derivatized with pentafluorobenzyl bromide for GC–MS analysis. Thiocyanate levels as low as 2.5 ng mL−1 and cyanide exposure levels as low as 175 μg kg−1 were detected. Samples analyzed from smokers and non-smokers using this method showed significantly different levels of protein-bound thiocyanate (p < 0.01). These results demonstrate the potential of this method to positively confirm chronic cyanide exposure through the analysis of protein-bound cyanide in human plasma.
Keywords: Thiocyanate; Protein adducts; Biomarker; Gas chromatography–mass spectrometry; Extraction; Bioanalysis; Derivatization;
An alternative method for analysis of food taints using stir bar sorptive extraction by Kathy Ridgway; Sam P.D. Lalljie; Roger M. Smith (29-36).
The determination of taints in food products currently can involve the use of several sample extraction techniques, including direct headspace (DHS), steam distillation extraction (SDE) and more recently solid phase microextraction (SPME). Each of these techniques has disadvantages, such as the use of large volumes of solvents (SDE), or limitations in sensitivity (DHS), or have only been applied to date for determination of individual or specific groups of tainting compounds (SPME). The use of stir bar sorptive extraction (SBSE) has been evaluated as a quantitative screening method for unknown tainting compounds in foods. A range of commonly investigated problem compounds, with a range of physical and chemical properties, were examined. The method was optimised to give the best response for the majority of compounds and the performance was evaluated by examining the accuracy, precision, linearity, limits of detection and quantitation and uncertainties for each analyte.For most compounds SBSE gave the lowest limits of detection compared to steam distillation extraction or direct headspace analysis and in general was better than these established techniques. However, for methyl methacrylate and hexanal no response was observed following stir bar extraction under the optimised conditions.The assays were carried out using a single quadrupole GC–MS in scan mode. A comparison of acquisition modes and instrumentation was performed using standards to illustrate the increase in sensitivity possible using more targeted ion monitoring or a more sensitive high resolution mass spectrometer. This comparison illustrated the usefulness of this approach as an alternative to specialised glassware or expensive instrumentation. SBSE in particular offers a ‘greener’ extraction method by a large reduction in the use of organic solvents and also minimises the potential for contamination from external laboratory sources, which is of particular concern for taint analysis.
Keywords: Food taints; Stir bar sorptive extraction; Headspace; Steam distillation extraction; GC–MS;
Highly sensitive chiral analysis of amino acids by in-line single drop microextraction and capillary electrophoresis with laser-induced fluorescence detection by Guodong Liang; Kihwan Choi; Ahmed Yacine Badjah Hadj Ahmed; Zeid A. ALOthman; Doo Soo Chung (37-42).
A highly sensitive method for chiral analysis of amino acids by in-line single drop microextraction (SDME) and chiral capillary electrophoresis (CE) with laser-induced fluorescence (LIF) detection was developed. In SDME, a drop of a basic aqueous acceptor phase covered with a thin organic layer was formed at the tip of a capillary by simple combination of sample-handling sequences of a CE apparatus. Then fluorescein isothiocyanate (FITC)-derivatized amino acids in an acidic donor solution were enriched into the drop through the organic layer. The enriched enantiomers were then resolved using a dual chiral selector of β-cyclodextrin (β-CD) and sodium taurodeoxycholate (STC). Here, in addition to serving as a labeling reagent providing high fluorescence signal, hydrophobic FITC was primarily used as a modifier aiding the extraction of zwitterionic amino acids by blocking the amino groups and increasing the hydrophobicity, yielding 220 times increase in extraction efficiency. Several hundred-fold enrichments were achieved with 10 min SDME, yielding LODs of 30–60 pM and enabling direct analysis of d-AAs in a 99% enantiomeric excess mixture. In view of no additional modification of the existing commercial CE instrument, this method without stirring can be easily realized using known operations. When a microstirrer was customized to the CE instrument several thousand-fold enrichments could be obtained with LODs in the low picomolar range of 1–3 pM.
Keywords: Amino acids; Chiral separation; Single drop microextraction; Capillary electrophoresis;
Analysis of terpenes in white wines using SPE–SPME–GC/MS approach by Mariusz Dziadas; Henryk H. Jeleń (43-49).
Terpenes contribute to some white wines aroma, especially these produced from Muscat grapes and others aromatic ones of high terpene contents (Gewürtztramminer, Traminer, Huxel, Sylvaner). Terpenes are present in wine in free and bound (in a form of glycosides) forms. Analyses of bound terpenes are usually performed using solid phase extraction after hydrolysis of glycosides. A new method for determination of terpenes from wine, focused on determination of terpenes released after acidic hydrolysis, based on solid phase extraction (SPE) followed by solid phase microextraction (SPME) was developed. Non-polar (free) and polar (bound terpenes) fractions were separated on 500 mg C18 cartridges. Bound terpenes were sampled using SPME immediately after acidic hydrolysis in non-equilibrium conditions. Application of combined SPE–SPME approach allowed quantification of selected terpenes in lower concentrations than in SPE approach and added a selectivity to the method, which enabled detection of compounds non-detectable in SPE extracts. Results obtained by SPE and SPE–SPME approach were correlated for free terpenes and those released after acid hydrolysis 20 white wines obtained from different grape varieties (R 2 = 0.923). Although developed for wine terpenes analysis, SPE followed by SPME approach has a great potential in analysis of other bound wine flavor compounds, especially those potent odorants present in trace amounts.
Keywords: Wine; Flavor compounds; Terpenes; Solid phase microextraction; Solid phase extraction gas chromatography/mass spectrometry;
Methane preconcentration in a microtrap using multiwalled carbon nanotubes as sorbents by Chutarat Saridara; Smruti Ragunath; Yong Pu; Somenath Mitra (50-54).
The GC monitoring of green house gases is a challenging task because the concentration of organic species such as methane are relatively low (ppm to ppb) and their analysis requires some level of preconcentration. Since methane is highly volatile, it is not easily retained on conventional sorbents. In this paper we present multiwalled carbon nanotubes (MWNTs) as an effective sorbent for a microtrap designed for methane preconcentration. Its performance was compared to other commercially available carbon based sorbents, and it was found to be the most effective sorbent in terms of breakthrough volume and enthalpy of adsorption.
Keywords: Microtrap; Multiwalled carbon nanotubes; Preconcentration; Gas chromatography; Methane;
Laser ablation single-collector inductively coupled plasma mass spectrometry for lead isotopic analysis to investigate evolution of the Bilbilis mint by M. Resano; M.P. Marzo; R. Alloza; C. Saénz; F. Vanhaecke; L. Yang; S. Willie; R.E. Sturgeon (55-63).
This work explores the performance of laser ablation—inductively coupled plasma mass spectrometry using different types of single-collector devices (sector field and time-of-flight instrumentation) for lead isotopic analysis of bronze coins, minted in the ancient city of Bilbilis. The aim of the study was achieving sufficient discrimination power to reveal similarities and differences for coins originating from different historical periods, and to obtain information on the possible source of the lead ores used in their production, while restricting the damage inflicted to the samples such that it is not visible to the naked eye.It was found that satisfactory results (RSD in the 0.15–0.30% range for 207Pb/206Pb and 208Pb/206Pb ratios) could be finally obtained, despite the noisy nature of signals generated upon ablation of the highly inhomogeneous coins, by means of a methodology based on: (a) selection of the line profiling ablation mode; (b) use of a dual pass spray chamber that permits the simultaneous introduction of a solution (containing thallium of known isotopic composition), thus resulting in a wet plasma that showed an increased robustness towards matrix effects and (c) detection using a TOF-ICPMS unit, which proved to be much better suited to deal with the transient signals obtained, while being also sufficiently sensitive to obtain good counting statistics, owing to the high lead level (average around 5%) present in the samples. Moreover, under these conditions, the simultaneous aspiration of the thallium spike permitted accurate correction for mass discrimination, such that it was not necessary to use external matrix-matched standards for calibration.
Keywords: Laser ablation; Inductively coupled plasma mass spectrometry; Time-of-flight; Pb isotope analysis; Roman coins;
Comparing roadsoils pollution patterns extracted by MOLMAP and classical three-way decomposition methods by M.P. Gómez-Carracedo; D. Ballabio; J.M. Andrade; J. Aires-de-Sousa; V. Consonni (64-71).
A recent approach based on self-organizing maps (SOMs) to extract patterns from three-way data, named MOLMAP, was applied in a four-seasons study on soil pollution and its results compared with three different conventional approaches: Parallel factor analysis (PARAFAC), matrix augmented principal components analysis (MA-PCA) and Procrustes rotation. Each sampling season comprised 92 roadsoil samples and 12 analytical variables (Cd, Co, Cu, Cr, Fe, Mn, Ni, Pb, Zn, loss on ignition, pH and humidity). It was found that all techniques yielded highly similar results as the samples became organized in two major groups, each with a differentiated pollution pattern. This confirmed MOLMAP as a reliable option to handle environmental three-way datasets and to extract accurate pollution patterns.
Keywords: Self-organizing maps; Parallel factor analysis; Matrix augmentation principal components analysis; Procrustes rotation; Soils; Heavy metals;
Synthetic approaches to parabens molecularly imprinted polymers and their applications to the solid-phase extraction of river water samples by A. Beltran; R.M. Marcé; P.A.G. Cormack; F. Borrull (72-78).
In this paper we describe the synthesis, characterisation and use of two distinct molecularly imprinted polymers (MIPs) prepared using esters of p-hydroxybenzoic acid (parabens) as templates: one MIP was synthesised by precipitation polymerisation using a semi-covalent molecularly imprinting strategy with methyl paraben as the template/target (MIP 1); the second MIP was prepared in monolithic form through a conventional non-covalent molecular imprinting strategy, with butyl paraben as the template (MIP 2). MIP 1 recognized methyl paraben, showed cross-selectivity for other parabens analytes used in the study and higher affinity towards these compounds than did a non-imprinted control polymer. Similarly, MIP 2 demonstrated higher affinity towards paraben analytes than a non-imprinted control polymer.For the analysis of environmental water samples, a solid-phase extraction (SPE) protocol was developed using MIP 2 as sorbent, and results were compared to a SPE using a commercial sorbent (Oasis HLB). With MIP 2 as sorbent and butyl paraben as target, when percolating 500 mL of river water spiked at 1 μg L−1 through the SPE cartridge, and using 1 mL of isopropanol as cleaning solvent, a higher recovery of butyl 4-hydroxybenzoate (butyl paraben) and a cleaner chromatogram where achievable when using the MIP compared to the commercial sorbent.
Keywords: Molecularly imprinted polymer; Parabens; Precipitation polymerisation; Semi-covalent approach; Sacrificial spacer;
Measurement of diffuse reflectance from combinatorial samples by F.A. Saeed; J.R.G. Evans (79-89).
Using a luminescence spectrometer as a platform, a system of fibre-optic probes was created that allows full colour characterisation, fluorescence and phosphorescence spectra to be recorded in diffuse reflectance and in transmission from thick or thin film arrays of combinatorial samples of diameter down to 2 mm and from liquids. An integrating sphere is not required and the method is more versatile than the instrument's fibre-optic plate reader which has conjoined fibre bundles set at a fixed angle. Incident and detected light is routed via separate optical fibre bundles which remain stationary above or below a two-axis table. The validation and calibration are described. A library of 25 members was scanned for both diffuse reflectance (colour) and fluorescence in less than an hour. The method thus combines techniques that conventionally rely on different instruments and makes them amenable for high throughput libraries.
Keywords: High throughput; Combinatorial; Colour measurement; Fluorescence; Diffuse reflectance;
Development and characterization of a magnetic bead-quantum dot nanoparticles based assay capable of Escherichia coli O157:H7 quantification by Gha-Young Kim; Ahjeong Son (90-96).
The development and characterization of a magnetic bead (MB)-quantum dot (QD) nanoparticles based assay capable of quantifying pathogenic bacteria is presented here. The MB-QD assay operates by having a capturing probe DNA selectively linked to the signaling probe DNA via the target genomic DNA (gDNA) during DNA hybridization. The signaling probe DNA is labeled with fluorescent QD565 which serves as a reporter. The capturing probe DNA is conjugated simultaneously to a MB and another QD655, which serve as a carrier and an internal standard, respectively. Successfully captured target gDNA is separated using a magnetic field and is quantified via a spectrofluorometer. The use of QDs (i.e., QD565/QD655) as both a fluorescence label and an internal standard increased the sensitivity of the assay. The passivation effect and the molar ratio between QD and DNA were optimized. The MB-QD assay demonstrated a detection limit of 890 zeptomolar (i.e., 10−21 mol L−1) concentration for the linear single stranded DNA (ssDNA). It also demonstrated a detection limit of 87 gene copies for double stranded DNA (dsDNA) eaeA gene extracted from pure Escherichia coli (E. coli) O157:H7 culture. Its corresponding dynamic range, sensitivity, and selectivity were also presented. Finally, the bacterial gDNA of E. coli O157:H7 was used to highlight the MB-QD assay's ability to detect below the minimum infective dose (i.e., 100 organisms) of E. coli O157:H7 in water environment.
Keywords: Magnetic bead; Quantum dot nanoparticles; E. coli O157:H7; eaeA gene; DNA hybridization-in-solution;