Analytica Chimica Acta (v.682, #1-2)

Desorption atmospheric pressure photoionization (DAPPI) is an ambient ionization technique for mass spectrometry (MS) that can be used to ionize polar as well as neutral and completely non-polar analytes. In this study polydimethylsiloxane (PDMS) was used as a solid phase extraction sorbent for DAPPI-MS analysis. Pieces of PDMS polymer were soaked in an aqueous sample, where the analytes were sorbed from the sample solution to PDMS. After this, the extracted analytes were desorbed directly from the polymer by the hot DAPPI spray solvent plume, without an elution step. Swelling and extracting the PDMS with a cleaning solvent prior to extraction diminished the high background in the DAPPI mass spectrum caused by PDMS oligomers. Acetone, hexane, pentane, toluene, diisopropylamine and triethylamine were tested for this purpose. The amines were most efficient in reducing the PDMS background, but they also suppressed the signals of low proton affinity analytes. Toluene was chosen as the optimum cleaning solvent, since it reduced the PDMS background efficiently and gave intensive signals of most of the studied analytes. The effects of DAPPI spray solvents toluene, acetone and anisole on the PDMS background and the ionization of analytes were also compared and extraction conditions were optimized. Anisole gave a low background for native PDMS, but toluene ionized the widest range of analytes. Analysis of verapamil, testosterone and anthracene from purified, spiked wastewater was performed to demonstrate that the method is suited for in-situ analysis of water streams. In addition, urine spiked with several analytes was analyzed by the PDMS method and compared to the conventional DAPPI procedure, where sample droplets are applied on PMMA surface. With the PDMS method the background ion signals caused by the urine matrix were lower, the S/N ratios of analytes were 2–10 times higher, and testosterone, anthracene and benzo[a]pyrene that were not detected from PMMA in urine, were observed in the MS spectrum.
Keywords: Desorption atmospheric pressure photoionization; Mass spectrometry; Polydimethylsiloxane; Solid phase extraction;

The study of mammalian soft tissue decomposition is an emerging area in forensic science, with a major focus of the research being the use of various chemical and biological methods to study the fate of human remains in the environment. Decomposition of mammalian soft tissue is a postmortem process that, depending on environmental conditions and physiological factors, will proceed until complete disintegration of the tissue. The major stages of decomposition involve complex reactions which result in the chemical breakdown of the body's main constituents; lipids, proteins, and carbohydrates. The first step to understanding this chemistry is identifying the compounds present in decomposition fluids and determining when they are produced. This paper provides an overview of decomposition chemistry and reviews recent advances in this area utilising analytical separation science.
Keywords: Decomposition chemistry; Analytical separations; Forensic science;

The large number of patients suffering from neurodegenerative diseases like Alzheimer's disease and Parkinson's disease motivates many research groups worldwide to investigate pathogenic factors and molecular mechanisms of these diseases. Recent studies and reviews indicate that metals are involved in these neurodegenerative processes in case their homeostasis in the brain is disturbed. Important is that the focus of these recent studies is on essential metals like Fe, Cu, Zn and Mn, but not on the well-known neurotoxic metals like Hg and Pb. Key issues for understanding metal induced neurotoxic effects are the transport processes across the neural barriers, the metal binding forms (species) and their interactions with neuronal structures. Total metal concentrations in cerebrospinal fluid were published in several studies for controls and patients, but the amount of reliable data sets is not yet sufficient for clear definition of normal and elevated levels.The need for more detailed information on metal species in CSF is highlighted in this review. However, studies on element speciation analysis, that means identification and quantification of the various binding forms of metals in cerebrospinal fluid, are rare. The major reasons therefore are difficulties in accessing cerebrospinal fluid samples, the non-covalent nature of many metal species of interest and their rather low concentrations. In spite of this, several applications demonstrate the potential of hyphenated techniques as additional diagnostic tools for cerebrospinal fluid analysis.This review shows the importance of trace element analysis and more specifically of element speciation in cerebrospinal fluid for an improved understanding of pathologic mechanisms promoting neuro-degeneration. Respective analytical techniques are also highlighted. Additionally, biochemical assays for selected high molecular mass metal species are summarized and critically discussed. Moreover additional potential techniques like direct non-invasive methods as well as mathematical modelling approaches are considered. Data on total concentrations of numerous elements in CSF as well as speciation information of elements such as Al, As, Ca, Cd, Cu, Fe, Mg, Mn, Hg, Pb, Se and Zn in CSF are summarized.
Keywords: Cerebrospinal fluid; Element speciation; Neurodegenerative disorders;

Ensemble wavelet modelling for determination of wheat and gasoline properties by near and middle infrared spectroscopy by Luiz Alberto Pinto; Roberto Kawakami Harrop Galvão; Mário César Ugulino Araújo (37-47).
The wavelet transform has been shown to be a useful tool for multivariate calibration. However, the choice of wavelet transform settings (wavelet family, length and number of decomposition levels) for a given application is still an open problem. The present paper proposes an alternative approach, which consists of generating an ensemble model by combining individual models obtained with different wavelet transform settings. The advantages of the proposed method are demonstrated in two analytical problems, namely the determination of moisture and protein in wheat by near infrared spectroscopy and the determination of specific mass and three distillation temperatures (T10, T50, T90) in gasoline by middle infrared spectroscopy. In these problems, the results varied considerably among individual models, which underlines the risk associated to an inadequate choice of wavelet transform settings. In contrast, the ensemble model always provided adequate results in terms of prediction error and noise sensitivity. The proposed method can be seen as an advantageous alternative for multivariate calibration in the wavelet domain, as it frees the analyst from the need to choose a particular configuration for the wavelet transform.
Keywords: Multivariate calibration; Wavelet transform; Combination of models; Near and middle infrared spectroscopy; Wheat; Gasoline;

Simple and sensitive methods have been developed for simultaneous detection of cyromazine, melamine and their metabolites (ammeline, ammelide and cyanuric acid) in samples of animal origins. These include a high performance liquid chromatography (HPLC) method and a liquid chromatography–tandem mass spectrometry (LC–MS/MS) method and are useful in regular monitoring and in toxicity studies of these molecules. Representative samples used in this study include muscles and livers of swine, bovine, sheep and chicken, kidneys of swine, bovine and sheep, and milk powder. A new sample preparation procedure with pressurized liquid extraction (PLE) at 1400 psi and 70 °C was investigated. Quantification of these five compounds by HPLC was achieved using an APS-2 column with UV detection at 230 nm. Limit of detection (LOD) was at 10 μg kg−1, and limit of quantification (LOQ) was at 40 μg kg−1. Recoveries of the five analytes in spiked samples ranged from 72.2% to 115.4% with RSD less than 12%. Confirmatory analysis of the analytes was performed using LC–MS/MS in selected reaction monitoring (SRM) mode. The LOD and LOQ were 5 μg kg−1 and 15 μg kg−1, respectively. This is the first simultaneous analysis of cyromazine, melamine, ammeline, ammelide and cyanuric acid residues in complex tissue samples using PLE and HPLC. It is expected that these methods will find many practical applications in evaluating the safety of cyromazine, melamine and their metabolites.
Keywords: Cyromazine; Melamine; Pressurized liquid extraction; High performance liquid chromatography; Liquid chromatography–tandem mass spectrometry; Food-producing animals;

Simultaneous measurements of As, Mo, Sb, V and W using a ferrihydrite diffusive gradients in thin films (DGT) device by Heléne Österlund; Sara Chlot; Mikko Faarinen; Anders Widerlund; Ilia Rodushkin; Johan Ingri; Douglas C. Baxter (59-65).
The ferrihydrite-backed DGT (diffusive gradients in thin films), recently developed for arsenic and phosphate measurements was, for the first time, characterized with respect to molybdate, antimonate, vanadate and tungstate determination. Arsenate was included in the characterization to allow comparison with literature data and thus provide quality control of the measurements. In addition to laboratory experiments, field measurements were carried out in a natural stream in northern Sweden affected by mine drainage. It was shown that ferrihydrite-DGT is suitable for simultaneous determination of labile arsenic, molybdate, antimonate, vanadate and tungstate over a wide pH range. Diffusion coefficients were estimated using two different methods; diffusion cell and direct uptake to DGT devices in synthetic solutions. Estimations of the coefficients using the direct uptake method were performed between pH 4 and 8. The results from the two methods agreed well irrespective of pH, except for molybdate and antimonate that showed decreased values at pH 8. Adsorption of the analytes to ferrihydrite gel-discs was rapid at all pH values. However, there was a tendency toward lower adsorption affinity for antimonate compared to the other anions. 100% recovery of accumulated analytes was achieved through complete dissolution of the ferrihydrite adsorbent using 1.4 mol L−1 HNO3 with 0.1 mol L−1 HF. From field sampling it was concluded that the opportunities for accurate antimonate and molybdate determination decrease at pH ≥ 8.7. DGT-labile concentrations were generally lower than dissolved concentrations. Relatively lower DGT concentrations, compared to dissolved (<0.45 μm), were observed under a period when ferric oxide precipitations were detected on the DGT protective filter.
Keywords: Diffusive gradients in thin films; DGT; Ferrihydrite; Oxyanions; Mine drainage;

Colloidal gold probe based rapid immunochromatographic strip assay for cortisol by Seema Nara; Vinay Tripathi; Harpal Singh; Tulsidas G. Shrivastav (66-71).
A rapid and semi-quantitative immunochromatographic strip (ICS) test for cortisol analysis in serum was developed. The test strip was based on a competitive assay format. Colloidal gold nanoparticles were synthesized and coupled with cortisol-3-carboxymethyloxime–adipic acid dihydrazide–bovine serum albumin (F-3-CMO–ADH–BSA) antigen to directly compete with cortisol in human serum samples. F-3-CMO–ADH–BSA–gold label and uncoupled colloidal gold nanoparticles were appropriately characterized using UV–vis spectroscopy, transmission electron microscopy and atomic force microscopy. Anticortisol antibody raised against F-3-CMO–BSA immunogen in New Zealand white rabbits was coated on the NC membrane as test line. Anti-BSA antibody was used as control line. The lower detection limit of the ICS test was 30 ng mL−1 with visual detection and was completed in 10 min. About 30 human serum samples were also analyzed by the developed strip test and their range of cortisol concentration was established. The developed ICS test is rapid, economic and user friendly.
Keywords: Immunochromatographic strip; Colloidal gold; Cortisol; Competitive assay; Antibody;

Selective determination of 2,4-xylenol by gas chromatography/supersonic jet/resonance-enhanced multiphoton ionization/time-of-flight mass spectrometry by Hiroko Tsukatani; Hiroki Okudaira; Osamu Shitamichi; Tomohiro Uchimura; Totaro Imasaka (72-76).
Gas chromatography/supersonic jet/resonance-enhanced multiphoton ionization/time-of-flight mass spectrometry (GC/SSJ/REMPI/TOF-MS) was employed for isomer-selective determination of 2,4-xylenol in river and seawater samples. The sample containing 2,4-xylenol was measured using argon, rather than helium, as the GC carrier gas to cool the analyte molecule sufficiently. The instrumental detection limit (IDL) achieved at a flow rate of 1 mL min−1 was 14 pg. Although this value was comparable to the value (ca. 10 pg) obtained by gas chromatography/electron impact/quadrupole mass spectrometry (GC/EI/QMS). When the flow rate was increased to 8 mL min−1, interference from the 2,5-xylenol isomer was completely suppressed. The IDL was degraded to 83 or 160 pg at a flow rate of 5 or 8 mL min−1, respectively. The recovery of 2,4-xylenol from the river and the seawater samples was 85 and 93%, respectively. The time for analysis was only 10 min per one sample in GC/SSJ/REMPI/TOF-MS. These results suggest that GC/SSJ/REMPI/TOF-MS is useful for the selective measurement of 2,4-xylenol, which has been designated a Class I chemical substance in the Pollutant Release and Transfer Register (PRTR).
Keywords: 2,4-Xylenol; Gas chromatography; Supersonic jet; Resonance-enhanced multiphoton ionization; Time-of-flight mass spectrometry;

Discrimination between ginseng from Korea and China by light stable isotope analysis by Micha Horacek; Ji-Sook Min; Sang-Cheol Heo; Gerhard Soja (77-81).
Ginseng is a health food and traditional medicine highly valued in Asia. Ginseng from certain origins is higher valued than from other origins, so that a reliable method for differentiation of geographical origin is important for the economics of ginseng production. To discriminate between ginseng samples from South Korea and PR China, 29 samples have been analyzed for the isotopic composition of the elements H, C and N. The results showed δ 2H values between −94 and −79‰, for δ 13C −27.9 to −23.7‰ and for δ 15N 1.3–5.4‰ for Chinese ginseng. Korean ginseng gave δ 2H ratios between −91 and −69‰, δ 13C ratios between −31.2 and −22.4‰ and δ 15N ratios between −2.4 and +7‰. Despite the overlap between the values for individual isotopes, a combination of the isotope systems gave a reasonable differentiation between the two geographic origins. Especially the statistically significant difference in δ 2H ratios facilitated the differentiation between Korean and Chinese ginseng samples.
Keywords: Food authenticity; Geographical origin; Stable isotope; Korea; China; Panax ginseng;

Simultaneous determination of polyether ionophores, macrolides and lincosamides in hen eggs by liquid chromatography–electrospray ionization tandem mass spectrometry using a simple solvent extraction by Bernardete Ferraz Spisso; Rosana Gomes Ferreira; Mararlene Ulberg Pereira; Mychelle Alves Monteiro; Tatiana Ávila Cruz; Rafaela Pinto da Costa; Adélia Mara Belém Lima; Armi Wanderley da Nóbrega (82-92).
A liquid chromatography–electrospray ionization tandem mass spectrometric (LC–ESI-MS/MS) method was developed and validated for the determination of residues of 6 polyether ionophores (lasalocid, maduramicin, monensin, narasin, salinomycin, semduramicin), 3 macrolides (erythromycin, tylosin, clarithromycin) and 1 lincosamide (lincomycin) in eggs. Nigericin was used as qualitative internal standard. Samples were deproteinizated/extracted with acetonitrile without pH adjustments. Aliquots of the extracts were evaporated and reconstituted for injection in the instrument operated in positive multiple reaction monitoring (MRM) mode. The stability of the antibiotics and the intensity of the formed ions were considered in order to select a suitable solvent for the reconstitution of the obtained dry extracts. No clean-up steps were required and matrix effects were controlled by sample dilution, selection of appropriate chromatographic conditions and reduced injection volume. Good within-laboratory reproducibility was obtained, with relative standard deviations (RSDR) from 4.0 (semduramicin at 5 μg kg−1) to 18.6 (erythromycin at 25 μg kg−1) for the ionophores and macrolides. Lincomycin showed the least precise results, with a maximum RSDR of 20.2% at 75 μg kg−1). Satisfactory decision limits (CCα) and detection capabilities (CCβ) were also attained. Method limits of detection (LODs) from 0.04 (salinomycin) to 1.6 μg kg−1 (lincomycin) were achieved. Method limits of quantification (LOQs) were from 0.14 to 5.3 μg kg−1 for the same drugs, respectively. All the LOQs, except that obtained for maduramicin were remarkably below the lowest validation level. The proposed method is suitable for routine application in commercial egg samples.
Keywords: Eggs; Polyether ionophores; Macrolides; Lincosamides; Validation; Tandem mass spectrometry;

Hapten synthesis, monoclonal antibody generation, and development of competitive immunoassays for the analysis of picoxystrobin in beer by Francesc A. Esteve-Turrillas; Javier Parra; Antonio Abad-Fuentes; Consuelo Agulló; Antonio Abad-Somovilla; Josep V. Mercader (93-103).
This paper describes the original synthesis of a functionalized derivative of the fungicide picoxystrobin and the generation of the first reported monoclonal antibodies against this strobilurin pesticide. The synthetic hapten was prepared by total synthesis from commercial chemicals and incorporating the spacer arm through a carbon–carbon single bond. Also, to obtain the immunogen, an uncommon hapten activation strategy based on N,N′-disuccinimidyl carbonate was employed, affording high activation yields and clean and reproducible coupling results. With these immunoreagents, two enzyme-linked immunosorbent assays (ELISAs) were developed: a competitive one-step assay using the antibody-coated direct ELISA format and a competitive two-step assay with the conjugate-coated indirect ELISA procedure. Both immunoassays were characterized in terms of sensitivity, selectivity, tolerance to solvents and matrix effects, achieving limits of detection below 0.2 μg L−1. The optimized assays were used for the determination of picoxystrobin residues in beer, with recovery values ranging between 90 and 121% for the direct assay and from 79 to 122% for the indirect assay.
Keywords: ELISA; Pesticide; Hapten synthesis; Protein coupling; Cereal; Food analysis;

Development and application of a quantitative lateral flow immunoassay for fumonisins in maize by Laura Anfossi; Marianna Calderara; Claudio Baggiani; Cristina Giovannoli; Enrico Arletti; Gianfranco Giraudi (104-109).
A quantitative lateral flow immunoassay for measuring fumonisins in maize was developed. Strip preparation and assay parameters were optimized to obtain a dipstick usable outside the laboratory with different samples, and which shows performance comparable with that of other screening methods, as confirmed by the intra- and the inter-day precision of data (RSD 5–16%). Quantification was obtained by an external calibration curve, which can be stored and used for measurements made with strips of the same batch in different days and at varying temperatures (22–37 °C). Limit of detection (120 μg L−1) and dynamic range (200–5000 μg L−1) allow the direct assessment of fumonisin contamination at all levels of regulatory relevance. Twenty-seven maize samples were analyzed after a simple sample preparation which avoids the use of organic solvent. Linear correlation was observed (y  = 1.071x  − 0.2, r 2  = 0.990) when data was compared with that obtained through a reference LC–MS/MS method, across a wide range of fumonisin contamination.
Keywords: Fumonisins; Lateral flow immunoassay; Quantitative assay; Maize;

Influence of the solvent on nature of gate effect in molecularly imprinted membrane by Yasuo Yoshimi; Rika Arai; Satomi Nakayama (110-116).
The solute diffusive permeability in a thin layer of a molecularly imprinted polymer (MIP) is affected by specific binding of the MIP with a template. This phenomenon, termed the “gate effect,” would be widely applicable for the development of novel biomimetic sensors. However, the mechanism underlying the gate effect is not totally understood. We present here investigation of the role of specific adsorption of a template and solution content in MIPs on the gate effect. A molecularly imprinted self-supporting membrane was formed by copolymerization of methacrylic acid, 2-vinylpyridine, and triethyleneglycol dimethacrylate in the presence of l- (or d-) phenylalanine as a template. The template adsorbed by membrane with degree of enantio-selectivity in a mixed solvent of methanol and water. The amount of adsorption and binding selectivity showed little sensitivity to the solvent composition. The solution content in the membrane increased with increasing the methanol concentration of the solvent following a sigmoid curve with an inflection point at methanol concentration of 20 wt.%. The content increased in the presence of the template at methanol concentrations higher than the inflection point, and decreased at lower methanol concentrations. The creatinine permeability across the membrane estimated by batchwise dialysis increased in the presence of the template at 50 wt.% methanol in the solvent, and did not change at 20 wt.%. There was no permeability for creatinine in the pure water solvent. Both the solution content and the permeability were not affected by the presence of the enantiomer of the template. The results show that the choice of solvent controls more strongly the nature of the gate effect than the specific binding of the template.
Keywords: Molecularly imprinted polymer; Gate effect; Chirality; Solution content; Adsorption; Permeability;

Efficient hydrophilic interaction liquid chromatography–tandem mass spectrometry for the multiclass analysis of veterinary drugs in chicken muscle by Chayada Chiaochan; Urairat Koesukwiwat; Soparat Yudthavorasit; Natchanun Leepipatpiboon (117-129).
A simple and sensitive method has been developed for multiresidue analysis of 24 important veterinary drugs (including 3 aminoglycosides, 3 β-lactams, 2 lincosamides, 4 macrolides, 4 quinolones, 4 sulfonamides, 3 tetracyclines, and amprolium) in chicken muscle. The method involved a simple extraction using (1:1, v/v) of 2% trichloroacetic acid in water–acetonitrile, followed by removing fat with hexane, dilution of sample extract, and filtration prior to liquid chromatography–tandem mass spectrometric (LC–MS/MS) analysis. Hydrophilic interaction liquid chromatography (HILIC) proved to be very effective for separation of a wide range of polar and hydrophilic compounds (providing high sensitivity and good peak shape) compared to reversed phase and ion-pair separation. The method was successfully validated according to the European Decision 2002/657/EC. Average recoveries were 53–99% at 0.5-MRL, MRL, and 1.5-MRL spiking levels, with satisfactory precision ≤15% RSD. The limit of detection of the method was 0.1–10 μg kg−1 for 22 analytes and 20 μg kg−1 for aminoglycosides. These values were lower than the maximum residue limits (MRLs) established by the European Union. The evaluated method provides reliable screening, quantification, and identification of 24 veterinary drug residues in foods of animal origin. It has been successfully tested in real samples (such as chicken muscle, shrimp, and egg).
Keywords: Veterinary drugs; Residue analysis; Chicken muscle; Hydrophilic interaction liquid chromatography; Tandem mass spectrometry;

Determination of 237Np and Pu isotopes in large soil samples by inductively coupled plasma mass spectrometry by Sherrod L. Maxwell; Brian K. Culligan; Vernon D. Jones; Sheldon T. Nichols; Maureen A. Bernard; Gary W. Noyes (130-136).
A new method for the determination of 237Np and Pu isotopes in large soil samples has been developed that provides enhanced uranium removal to facilitate assay by inductively coupled plasma mass spectrometry (ICP-MS). This method allows rapid preconcentration and separation of plutonium and neptunium in large soil samples for the measurement of 237Np and Pu isotopes by ICP-MS. 238U can interfere with 239Pu measurement by ICP-MS as 238UH+ mass overlap and 237Np via 238U peak tailing. The method provides enhanced removal of uranium by separating Pu and Np initially on TEVA Resin, then transferring Pu to DGA resin for additional purification. The decontamination factor for removal of uranium from plutonium for this method is greater than 1 × 106. Alpha spectrometry can also be applied so that the shorter-lived 238Pu isotope can be measured successfully. 239 Pu, 242Pu and 237Np were measured by ICP-MS, while 236Pu and 238Pu were measured by alpha spectrometry.
Keywords: Plutonium; Neptunium; Large soil; Lanthanum fluoride; ICP-MS;