Check out our New Publishers' Select for Free Articles

Analytical and Bioanalytical Chemistry (v.387, #3)

Reinventing yourself: marketing the experienced chemist in today’s job market by John Fetzer (pp. 727-728).

is the author or co-author of over 130 research articles, reviews, and book chapters. He is a member of the International Advisory Board of Analytical and Bioanalytical Chemistry. Dr. Fetzer worked for over 20 years as an analytical chemist for the Chevron Corporation and now runs his own consulting company, Fetzpahs Consulting, in Hercules, CA, USA. His book Career Management for Chemists—A Guide to Success in a Chemistry Career was published by Springer.

Mahmoud H. Hamdan, Pier G. Righetti (Eds.): Proteomics today: protein assessment and biomarkers using mass spectrometry, 2D electrophoresis and microarray technology by Edward S. Yeung (pp. 729-730).

Simon Nelms (Ed.): Inductively Coupled Plasma Mass Spectrometry Handbook by Sergei F. Boulyga (pp. 731-732).

Carsten Reinhardt: Shifting and rearranging. Physical methods and the transformation of modern chemistry by Freddy C. Adams (pp. 733-734).

Archaeometry, an interdisciplinary approach by Peter Vandenabeele (pp. 735-735).

Scanning electron microscopy and energy dispersive analysis: applications in the field of cultural heritage by Manfred Schreiner; Michael Melcher; Katharina Uhlir (pp. 737-747).

Scanning electron microscopy has been extensively used for the material characterization of objects of artistic and archaeological importance, especially in combination with energy dispersive X-ray microanalysis (SEM/EDX). The advantages and limitations of SEM/EDX are presented in a few case studies: analysis of pigments in cross-sections of paint layers, quantitative analysis of archaeological glass from the Roman period excavated in Ephesos/Turkey, and investigations on glasses with medieval composition concerning their weathering stability and degradation phenomena.

Keywords: Scanning electron microscopy (SEM); Energy dispersive analysis (EDX); Art analysis; Pigment; Glass; Authentication; Degradation; Weathering

Laser-induced breakdown spectroscopy (LIBS) in archaeological science—applications and prospects by Anastasia Giakoumaki; Kristalia Melessanaki; Demetrios Anglos (pp. 749-760).

Laser-induced breakdown spectroscopy (LIBS) has emerged in the past ten years as a promising technique for analysis and characterization of the composition of a broad variety of objects of cultural heritage including painted artworks, icons, polychromes, pottery, sculpture, and metal, glass, and stone artifacts. This article describes in brief the basic principles and technological aspects of LIBS, and reviews several test cases that demonstrate the applicability and prospects of LIBS in the field of archaeological science.

Keywords: Archaeology; Archaeometry; LIBS; Laser ablation; Elemental analysis

Laser interference-based techniques and applications in structural inspection of works of art by Vivi Tornari (pp. 761-780).

Techniques based on laser interferometry principles provide great potential to retrieve imperceptible bulk information regarding the physical and mechanical condition of complex and inhomogeneous structures. This review presents the progress in and prospects for optical coherent interferometry techniques in artwork conservation applications, in particular concerning the performance of the developed instrumentations and methodologies. Each of the state-of-the-art techniques is introduced by reference to fundamental principles, basic equations and general optical geometry. In this context, a brief introduction to fundamental principles governing the optical coherent interferometry measurements is presented prior to discussion on performance. Some exemplary results demonstrating that bulk interferometric signals can be obtained from rough artwork surfaces are shown and their suitability is reviewed. Several opportunities for art conservation research and applications are summarised and discussed.

Keywords: Optical metrology; Optical coherent interferometry; Holography; Holographic interferometry; Speckle pattern interferometry; Shearography; Vibrometry; Art conservation

Spatially resolved element analysis of historical violin varnishes by use of μPIXE by Alex von Bohlen; Stefan Röhrs; Joseph Salomon (pp. 781-790).

External μPIXE has been used for characterisation of small samples of varnish from historical violins, and pieces of varnished wood from historical and modern stringed instruments. To obtain spatially resolved information about the distribution of elements across the varnish layers single-spot analysis, line-scans, and area-mapping were performed. Local resolution of approximately 20 μm was obtained from the 3 MeV, 1 nA proton micro-probe. Results from simultaneous multi-element determination of Na, Mg, Al, Si, P, S, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Br, Rb, Sr, Ag, Cd, Sn, Ba, and Pb in historical varnishes are presented. Semi-quantitative evaluation of line-scans recorded on diverse historical varnishes is reported. The applied method is discussed in detail and the results obtained are critically reviewed and compared with those in the literature.

Keywords: μPIXE; Violin varnish; Element distribution; Spatial resolved analysis; Cultural heritage

Noninvasive methods for the investigation of ancient Chinese jades: an integrated analytical approach by Francesca Casadio; Janet G. Douglas; Katherine T. Faber (pp. 791-801).

This paper reports on an integrated analytical approach for the noninvasive characterization of Chinese nephrite samples, encompassing both geological reference specimens and museum objects. Natural variations induced by cationic substitutions, as well as human-induced alterations such as heating, which both affect color, are the focus of this contribution. Totally noninvasive methods of analysis were used, including X-ray fluorescence spectroscopy, Raman microspectroscopy, visible reflectance spectroscopy and X-ray diffraction; moreover, the feasibility of using a portable Raman spectrometer for the in-field identification of jades has been demonstrated. Fe/Fe+Mg (% p.f.u.) ratios of the jades have been calculated based on hydroxyl stretching Raman bands, which will provide an important addition to similar data that are being collected at major museums in the Western and Eastern hemispheres.

Keywords: Jade; Nephrite; XRD; Raman spectroscopy; Visible spectrophotometry

The contribution of gas chromatography to the resynthesis of the post-Byzantine artist’s technique by Eleni Kouloumpi; Graham Lawson; Vassilios Pavlidis (pp. 803-812).

Gas chromatographic analysis of ethyl chloroformate derivatives of samples taken from the paint layers of post-Byzantine panel paintings permitted the successful characterisation of the different binding media used in them. This paper describes an analytical study of various post-Byzantine binding media such as egg yolk and egg/oil emulsion, using gas chromatography. The characterisation of these icons’ binding media is an important task, as it contributes to our understanding of and the reconstruction of the post-Byzantine artists’ palette. It also enables us to investigate the validity of our assumptions about the influences of Venetian style on Greek icon painting techniques from the sixteenth to the early nineteenth century, which up to now have been based on information in artists’ handbooks. The methodology involves two experimental steps: (1) hydrolysis of the proteins and triglycerides in the binding media to obtain free amino acids and fatty acids, and (2) the formation of ethyl chloroformate derivatives via derivatization with ethyl chloroformate (ECF). This methodology is of considerable interest, since it permits the identifcation of the nature of the proteinaceous binders used in these works through the simultaneous derivatization and determination of amino acids and fatty acids. Advantages of this methodology include the small quantity of sample required and the minimum preparation time involved. The proteinaceous media can be determined based on the ratios of seven stable amino acids, while the type of emulsions and drying oils used can be determined from the fatty acid ratio.

Keywords: Post-Byzantine icon paintings; Binding media identification; Egg tempera; Ethyl chloroformate derivatives; Gas chromatography

Non-destructive analysis of museum objects by fibre-optic Raman spectroscopy by Peter Vandenabeele; Jim Tate; Luc Moens (pp. 813-819).

Raman spectroscopy is a versatile technique that has frequently been applied for the investigation of art objects. By using mobile Raman instrumentation it is possible to investigate the artworks without the need for sampling. This work evaluates the use of a dedicated mobile spectrometer for the investigation of a range of museum objects in museums in Scotland, including antique Egyptian sarcophagi, a panel painting, painted surfaces on paper and textile, and the painted lid and soundboard of an early keyboard instrument. The investigations of these artefacts illustrate some analytical challenges that arise when analysing museum objects, including fluorescing varnish layers, ambient sunlight, large dimensions of artefacts and the need to handle fragile objects with care. Analysis of the musical instrument (the Mar virginals) was undertaken in the exhibition gallery, while on display, which meant that interaction with the public and health and safety issues had to be taken into account. Experimental set-up for the non-destructive Raman spectroscopic investigation of a textile banner in the National Museums of Scotland

Keywords: Raman spectroscopy; Conservation science; Art analysis; Non-destructive investigation; Mobile Raman equipment

Raman spectroscopic analysis of human remains from a seventh century cist burial on Anglesey, UK by Howell G. M. Edwards; Andrew S. Wilson; Nik F. Nik Hassan; Andrew Davidson; Andrew Burnett (pp. 821-828).

Specimens from human remains exhibiting unusual preservation excavated from a seventh century stone cist burial at Towyn y Capel in Anglesey, UK, have been analysed using Raman spectroscopy with near-infrared laser excitation at 1,064 and 785 nm. Specimens of hair and bone provided evidence for severe degradation and microbial colonisation. The deposits within the stone cist showed that some microbially mediated compounds had been formed. Analysis of crystals found at the interface between the hair and the skeletal neck vertebrae revealed a mixture of newberyite and haematite, associated with decomposition products of the hair and bone. An interesting differential degradation was noted in the specimens analysed which could be related to the air-void and the presence of plant root inclusions into the stone cist. This is the first time that Raman spectroscopy has been used in the forensic archaeological evaluation of burial remains in complex and dynamic environments.

Keywords: Raman spectroscopy; Cist burial; Degradation; Hair; Bone; Newberyite; Forensic

Combined FT–Raman spectroscopic and mass spectrometric study of ancient Egyptian sarcophagal fragments by Howell G. M. Edwards; Ben Stern; Susana E. Jorge Villar; A. Rosalie David (pp. 829-836).

The application of combined Raman spectroscopic and GC–MS analytical techniques for the characterisation of organic varnish residues from Egyptian Dynastic funerary sarcophagal and cartonnage fragments from the Graeco-Roman period, ca. 2200 BP, is described. The nondestructive use of Raman spectroscopy was initially employed to derive information about the specific location of organic material on the specimens, which were then targeted in specific areas using minimal sampling for GC–MS analysis. In the case of the sarcophagal fragment, a degraded yellow-brown surface treatment was identified as a Pistacia spp. resin; this provides additional evidence for the use of this resin, which has previously been identified in Canaanite transport amphorae, varnishes and “incense” bowls in an Egyptian Late Bronze Age archaeological context. The cartonnage fragment also contained an organic coating for which the Raman spectrum indicated a degradation that was too severe to facilitate identification, but the GC–MS data revealed that it was composed of a complex mixture of fatty acid residues. The combined use of GC–MS and Raman spectroscopy for the characterisation of organic materials in an archaeological context is advocated for minimisation of sampling and restriction to specifically identified targets for museum archival specimens.

Keywords: Raman spectroscopy; Mass spectrometry; Egyptian Dynastic sarcophagi; Cartonnage; Resins; Pistacia ; Residue analysis

The de Brécy Madonna and Child tondo painting: a Raman spectroscopic analysis by Howell G. M. Edwards; Timothy J. Benoy (pp. 837-846).

Raman spectra have been obtained from a Madonna and Child tondo painting, known as the de Brécy Tondo. Despite the provision of only a small number of microscopic samples, definitive spectra were obtained from mineral pigments. From one specimen, spectra of an organic binder enabled the consideration of several possibilities to be accomplished and a suggestion proposed for the medium. In another specimen the identification of the spectral signatures of Prussian blue, which was only synthesised some 200 years after the predicated date of execution of the painting, indicated that some unrecorded restoration had been undertaken later in the painting’s history. Research* carried out on this tondo from 1987 to 1991 indicated the probability that it is the work of Raphael, a conclusion supported by further research recently undertaken on the provenance. The stylistic similarity of the tondo to Raphael’s Sistine Madonna is very clear; the pigments identified in this analysis are consistent with a Renaissance attribution for the de Brécy Tondo.

Keywords: Raphael; Raman spectroscopy; Renaissance art; Madonna; Pigments; Tondo painting

Non-invasive and non-destructive micro-XRF and micro-Raman analysis of a decorative wallpaper from the beginning of the 19th century by Kepa Castro; Maite Pérez-Alonso; María Dolores Rodríguez-Laso; Nestor Etxebarria; Juan Manuel Madariaga (pp. 847-860).

Non-destructive and non-invasive micro-Raman fibre optic and micro-XRF analyses were performed to study a wallpaper from the beginning of the 19th century. The complementarity of these two non-destructive techniques is shown in this work. The analysed artwork is considered one of the most beautiful wallpapers ever manufactured according to the catalogues and books; it is known as Chasse de Compiègne, manufactured by Jacquemart, Paris, in 1812. During the analysis, an unexpected pigment was detected by both analytical techniques: lead-tin yellow type II. This pigment was used until ca. 1750, when other yellow pigments replaced it, thus it is very difficult to find it in paintings afterwards. Together with this pigment, red lead, Prussian blue, brochantite, yellow iron oxide, calcium carbonate, vermilion, carbon black of animal origin (bone black), lead white, and raw and burnt sienna were also determined by combining the analytical information provided by both techniques. A possible degradation of brochantite to antlerite is also discussed.

Keywords: Pigment; Wallpaper; Raman; XRF; Artwork; Basic copper sulphate

Insights into electrolytic stabilization with weak polarization as treatment for archaeological copper objects by Annemie Adriaens; Mark Dowsett; Karen Leyssens; Bjorn Van Gasse (pp. 861-868).

Immersion of corroded copper artefacts in dilute sodium sesquicarbonate solution is a well-recognized stabilization technique—especially in the conservation of objects recovered from marine environments and therefore saturated with chlorides. Here we describe three linked experiments performed to investigate a variation on this treatment, involving the application of a low potential to the artefact in order to drive the chloride extraction process. This includes a new spectroelectrochemical approach which allows 2-D pseudorandom X-ray reflection diffraction patterns to be obtained without interrupting the reaction in solution. Experiments were carried out on synthetically produced chloride layers on copper (nantokite and atacamite). We show that a thick chloride layer is, in general, replaced by a thin cuprite layer through a mechanism which involves detachment of the chloride crystallites from the surface prior to dissolution.

Keywords: Cultural heritage; Conservation; Stabilization; Cupreous objects; Spectroelectrochemistry; SR-XRD; Chronoamperometry

Some new trends in the ionoluminescence of minerals by H. Calvo del Castillo; J. L. Ruvalcaba; T. Calderón (pp. 869-878).

Ionoluminescence (IL) has mainly been used to detect impurities or defects inside synthetic materials. This paper gives a summary of new applications of IL to natural minerals that might be found in ancient pieces of jewellery or decorative artefacts (affreschi, stucchi, mosaics). Some relevant examples of its use for archaeometrical purposes are given to highlight the potential of the technique. Chemical information can be obtained by luminescent characterization of minerals. IL spectra act as digital imprint for elements or defects inside each material, enabling differentiation of natural specimens from imitations and/or synthetic analogues. Crystal field theory indicates it is the coordination number of the emitter inside the crystalline structure that gives information on its valence. Historical confusion between rubies and red spinel can easily be resolved by analysis of IL spectra. Modern synthetic diamonds can also be discriminated and blue sapphire can be distinguished from blue kyanite, a silicate that is currently being sold as its imitation. The technique can also differentiate between the synthetic and the natural gems. Polymorphs can be identified, and it is possible to recognize minerals from isomorphic series (from the same chemical group with the same structure) even when they share the same light emitter (e.g. Mn²⁺, in carbonates). High-quality glasses (e.g. laser glasses) which are normally used for faking gemstones can be also detected. We fully believe IL will, in the future, be a powerful technique for determining the crystallinity of solids. This paper gives an overview of possible applications of IL to archaeometry for mineral characterization; this is a new application that still requires further study.

Keywords: Ionoluminescence; Minerals; Gemstones; Synthetic analogues; Imitations; Crystal field theory

Comparison of multivariate calibration models for glucose, urea, and lactate from near-infrared and Raman spectra by Min Ren; Mark A. Arnold (pp. 879-888).

Partial least-squares (PLS) calibration models have been generated from a series of near-infrared (near-IR) and Raman spectra acquired separately from sixty different mixed solutions of glucose, lactate, and urea in aqueous phosphate buffer. Independent PLS models were prepared and compared for glucose, lactate, and urea. Near-IR and Raman spectral features differed substantially for these solutes, with Raman spectra enabling greater distinction with less spectral overlap than features in the near-IR spectra. Despite this, PLS models derived from near-IR spectra outperformed those from Raman spectra. Standard errors of prediction were 0.24, 0.11, and 0.14 mmol L⁻¹ for glucose, lactate, and urea, respectively, from near-IR spectra and 0.40, 0.42, and 0.36 mmol L⁻¹ for glucose, lactate, and urea, respectively, from Raman spectra. Differences between instrumental signal-to-noise ratios were responsible for the better performance of the near-IR models. The chemical basis of model selectivity was examined for each model by using a pure component selectivity analysis combined with analysis of the net analyte signal for each solute. This selectivity analysis showed that models based on either near-IR or Raman spectra had excellent selectivity for the targeted analyte. The net analyte signal analysis also revealed that analytical sensitivity was higher for the models generated from near-IR spectra. This is consistent with the lower standard errors of prediction.

Keywords: Near-infrared spectroscopy; Raman spectroscopy; Noninvasive glucose sensing; Multivariate calibration

Single eye analysis and contralateral eye comparison of tear proteins in normal and dry eye model rabbits by MALDI-ToF mass spectrometry using wax-coated target plates by Bryan M. Ham; Jean T. Jacob; Richard B. Cole (pp. 889-900).

A study of rabbit tear protein expression in a dry eye rabbit model was performed to determine if a pattern in expressed proteins could be identified. The uniqueness of the model allows the comparison of normal (control) eye tear protein expression with surgically induced dry eye tear protein expression in individual animals. The sensitivity of the method allows for single eye analysis. One-dimensional mini-gel electrophoresis of the tear proteins did not show substantial differences between band patterns of the normal versus the dry eye, but was used to assess the molecular weight ranges of the major proteins. Specific assignments of some of the predominant proteins were obtained by tandem mass spectrometry (MS) which showed that the lower molecular weight lipid-binding proteins (approximately 10 kDa to 36 kDa) constitute a considerable amount of the observed protein, followed in lesser quantities by the transferrins which have higher molecular weights ranging from 70 kDa to 85 kDa. Enhancement of matrix-assisted laser desorption/ionization time-of-flight (MALDI-ToF) MS linear mode analysis of intact proteins in tear fluid was demonstrated through the use of wax-coated MALDI plates and spot washing. MALDI-ToF MS analysis of the expressed tear proteins illustrates that differences between normal eye tear and dry eye tear protein content are manifested in changes in the lower molecular weight lipid-binding proteins such as lipophilin which exhibits an increase in concentration in the dry eye, and β-2 microglobulin which undergoes a decrease.

Keywords: Proteomics; Dry eye; Wax coat; Lipophilin; Microglobulin

Size prediction of recombinant human growth hormone nanoparticles produced by supercritical fluid precipitation by Dongjin Pyo; Changhyun Lim; Donghun Cho; Dahlkyun Oh (pp. 901-907).

Solution-enhanced dispersion by supercritical fluids (SEDS) was applied to produce nano-sized recombinant human growth hormone (hGH) particles. Ethanol was used to help the supercritical carbon dioxide to extract water from the aqueous protein solution. Various sizes of hGH nanoparticles were successfully prepared with a narrow particle size distribution from aqueous ethanol solution without using any additive. The theoretical particle sizes were deduced from the calculated droplet sizes based on a modified Jasuja’s equation. The calculated mean particle sizes and the experimentally obtained ones were compared and the results showed an excellent correlation coefficient (R ²) of 0.995. Figure Distribution of hGH Nano-particles

Keywords: Nanoparticle; Supercritical fluid; Human growth hormone

Studies on interactions of programmed cell death 5 (PDCD5) and its related peptides with heparin by capillary zone electrophoresis by Xiaomei Ling; Yi Liu; Hui Fan; Yingcheng Zhong; Dan Li; Ying Wang (pp. 909-916).

Capillary zone electrophoresis (CZE) was used to investigate interactions between heparin and programmed cell death 5 (PDCD5), and between heparin and PDCD5-related peptides. Samples containing PDCD5, PDCD5-related peptides, and heparin at various ratios were incubated at room temperature and then separated by CZE with tris-acetate buffer at pH 7.2. Both qualitative and quantitative characterizations of the binding of PDCD5 and PDCD5-related peptides to heparin were determined. The changes in the signals of PDCD5 and PDCD5-related peptides were monitored by comparing the electropherograms of the mixtures containing PDCD5 and heparin and PDCD5-related peptides and heparin with that of PDCD5 or PDCD5-related peptides only. The binding constant of the interaction between PDCD5 and heparin was calculated as 4.17 × 10⁴ M⁻¹ by Scatchard analysis. Our investigations show that it is possible to characterize the interaction between PDCD5 and heparin quantitatively and the interaction between PDCD5-related peptides and heparin qualitatively using CZE.

Keywords: Capillary zone electrophoresis; PDCD5; Heparin; VV8; Tat-NBD

Sensitive and selective determination of glutathione in probiotic bacteria by capillary electrophoresis–laser induced fluorescence by Alessandro Musenga; Roberto Mandrioli; Paolo Bonifazi; Ernst Kenndler; Anna Pompei; Maria Augusta Raggi (pp. 917-924).

Glutathione (GSH) is a thiol with an important function in protecting tissue against the oxidative stress which has been related to carcinogenesis in the colon. For this reason the development of probiotic species producing glutathione could be of great interest. To determine the glutathione content of some probiotic bacteria of the Bifidobacterium and Lactococcus genera, a very sensitive and selective analytical method based on capillary electrophoresis coupled to laser-induced fluorescence detection has been developed. Pretreatment of cell-lysate samples is very simple—precipitation of protein with acetonitrile in 1:2 volume ratio. The fluorophore 5-iodoacetamidofluorescein (5-IAF) was chosen for glutathione derivatisation; it reacts with thiols at pH 12.5, forming a fluorescent adduct which is excited by a laser at 488 nm for detection. The reaction conditions optimised were temperature, time, and 5-IAF/GSH molar ratio. Electrophoresis was performed with a carbonate buffer (25 mmol L⁻¹, pH 9.8) as background electrolyte and a voltage of 30 kV; an electrophoretic run was complete in less than 7 min. There was a good linear relationship between concentration and response in the range 2.5–500 ng mL⁻¹ and the LOD was 0.5 ng mL⁻¹. The glutathione content of probiotic cells was determined by using the standard additions method to reduce matrix effects. The method was fully validated and shown to be of suitable sensitivity and selectivity for determination of GSH in probiotic cell lysates.

Keywords: Glutathione; 5-Iodoacetamidofluorescein; Capillary electrophoresis; Laser-induced fluorescence; Probiotics

Chemiluminescent imaging analysis of interferon alpha in serum samples by Lingyan Hou; Zhujun Zhang; Lirong Luo (pp. 925-931).

Enzyme-linked immunosorbent assay (ELISA), horseradish peroxidase (HRP)-catalyzed fluorescent reaction, and oxalate chemiluminescence imaging analysis have been combined to develop a sensitive, simple, and rapid method for analysis of interferon alpha (α-IFN) in human serum samples. A typical “sandwich type” immunoassay was used. Reaction of o-phenylenediamine (OPD) with hydrogen peroxide (H₂O₂), catalyzed by HRP, produced 2,3-diaminophenazine (PDA), which was detected by chemiluminescence imaging analysis with the bis(2,4,6-trichlorophenyl)oxalate (TCPO)–H₂O₂–glyoxaline–PDA chemiluminescent system. The TCPO chemiluminescent imaging system is more sensitive and the chemiluminescence quantum yield is at least five times higher than for the luminol–H₂O₂–HRP–PIP (p-iodophenol) chemiluminescent imaging system. The results showed there was a very good linear correlation between response and amount of α-IFN in the range 1.3–156.0 pg mL⁻¹ (R = 0.9991) and the detection limit was 0.8 pg mL⁻¹ (S/N=3). The relative standard deviation (n = 9) was 4.7%. The proposed method has been used for successful analysis of the amount of α-IFN in human serum. The results obtained compared well with those obtained by conventional colorimetric ELISA and luminol chemiluminescent ELISA. Figure Procedures of the proposed method

Keywords: Interferon alpha; Enzyme-linked immunosorbent assays; Horseradish peroxidase-catalyzed fluorescent reaction; Chemiluminescence imaging analysis

Electrochemical study of brucine on an electrode modified with magnetic carbon-coated nickel nanoparticles by Sheng-Fu Wang; Fen Xie; Ruo-Fei Hu (pp. 933-939).

A novel type of glassy carbon electrode modified with magnetic carbon-coated nickel nanoparticles (C-Ni/GCE) was fabricated and the electrochemical properties of brucine were studied using it. The carbon-coated nickel nanoparticles showed excellent electrocatalytic activity for the redox of brucine and an enhanced electron transfer rate. The electrochemical behavior of brucine on the C-Ni/GCE was explored by cyclic voltammetry (CV), and a redox mechanism for brucine was proposed. A series of electrochemical parameters were calculated for brucine by CV and controlled-potential electrolysis. The C-Ni/GCE showed good sensitivity, selectivity and stability, and was applied to determine the concentration of brucine. The differential pulse voltammetry (DPV) response of the C-Ni/GCE showed that the catalytic current was linear with the concentration of brucine in the range of 4.7 × 10⁻⁸ to 2.4 × 10⁻⁴ mol l⁻¹, with a correlation coefficient of 0.998. The detection limit was 1.4 × 10⁻⁸ mol l⁻¹.

Keywords: Carbon-coated nickel; Magnetic nanoparticles; Brucine; Electrochemical redox mechanism; Determination

Reliability and uncertainty in the estimation of pK _a by least squares nonlinear regression analysis of multiwavelength spectrophotometric pH titration data by Milan Meloun; Tomáš Syrový; Sylva Bordovská; Aleš Vrána (pp. 941-955).

When drugs are poorly soluble then, instead of the potentiometric determination of dissociation constants, pH-spectrophotometric titration can be used along with nonlinear regression of the absorbance response surface data. Generally, regression models are extremely useful for extracting the essential features from a multiwavelength set of data. Regression diagnostics represent procedures for examining the regression triplet (data, model, method) in order to check (a) the data quality for a proposed model; (b) the model quality for a given set of data; and (c) that all of the assumptions used for least squares hold. In the interactive, PC-assisted diagnosis of data, models and estimation methods, the examination of data quality involves the detection of influential points, outliers and high leverages, that cause many problems when regression fitting the absorbance response hyperplane. All graphically oriented techniques are suitable for the rapid estimation of influential points. The reliability of the dissociation constants for the acid drug silybin may be proven with goodness-of-fit tests of the multiwavelength spectrophotometric pH-titration data. The uncertainty in the measurement of the pK _a of a weak acid obtained by the least squares nonlinear regression analysis of absorption spectra is calculated. The procedure takes into account the drift in pH measurement, the drift in spectral measurement, and all of the drifts in analytical operations, as well as the relative importance of each source of uncertainty. The most important source of uncertainty in the experimental set-up for the example is the uncertainty in the pH measurement. The influences of various sources of uncertainty on the accuracy and precision are discussed using the example of the mixed dissociation constants of silybin, obtained using the SQUAD(84) and SPECFIT/32 regression programs.

Keywords: Measurement uncertainty; Spectrophotometric titration; Dissociation constant; Protonation; pK _a reliability; Regression triplet; Residuals; Outliers; Influential points; Goodness-of-fit test; Silybin; SPECFIT; SQUAD; INDICES

Development and implementation of the CCME Reference Method for the Canada-Wide Standard for Petroleum Hydrocarbons (PHC) in soil: a case study by Richard Turle; Ted Nason; Harold Malle; Peter Fowlie (pp. 957-964).

Petroleum hydrocarbons have historically been analyzed by a wide variety of test methods. Interlaboratory studies have shown that standardization of both extraction and gas chromatographic analysis improved interlaboratory variability in hydrocarbon analysis. The Canadian Council of Ministers of the Environment has required a reference method for use with the Canada-wide standard for petroleum hydrocarbons. The process for developing and validating this method is described. This method requires the determination of 4 hydrocarbon fractions, namely, F1 (nC6 to nC10), F2 (>nC10 to nC16), F3 (>nC16 to nC34) and, F4 (nC35+), using GC-FID or gravimetry. The Tier 1 method was validated in a single laboratory study. This validated method was subjected to interlaboratory studies to determine its applicability and precision.

Keywords: Petroleum hydrocarbons; Interlaboratory studies; Contaminated soil; Canada-Wide Standard

An improved method for the analysis of volatile polyfluorinated alkyl substances in environmental air samples by Annika Jahnke; Lutz Ahrens; Ralf Ebinghaus; Urs Berger; Jonathan L. Barber; Christian Temme (pp. 965-975).

This article describes the optimisation and validation of an analytical method for the determination of volatile polyfluorinated alkyl substances (PFAS) in environmental air samples. Airborne fluorinated telomer alcohols (FTOHs) as well as fluorinated sulfonamides and sulfonamidoethanols (FOSAs/FOSEs) were enriched on glass-fibre filters (GFFs), polyurethane foams (PUFs) and XAD-2 resin by means of high-volume air samplers. Sensitive and selective determination was performed using gas chromatography/chemical ionisation–mass spectrometry (GC/CI–MS). Five mass-labelled internal standard (IS) compounds were applied to ensure the accuracy of the analytical results. No major blank problems were encountered. Recovery experiments were performed, showing losses of the most volatile compounds during extraction and extract concentration as well as strong signal enhancement for FOSEs due to matrix effects. Breakthrough experiments revealed losses of the most volatile FTOHs during sampling, while FOSAs/FOSEs were quantitatively retained. Both analyte losses and matrix effects could be remediated by application of adequate mass-labelled IS. Method quantification limits (MQLs) of the optimised method ranged from 0.2 to 2.5 pg/m³ for individual target compounds. As part of the method validation, an interlaboratory comparison of instrumental quantification methods was conducted. The applicability of the method was demonstrated by means of environmental air samples from an urban and a rural location in Northern Germany. Figure High-volume air sampling of volatile polyfluorinated alkyl substances using glass fibre filters and PUF/XAD-2 cartridges at a background monitoring site (Waldhof, Germany)

Keywords: Fluorotelomer alcohols; Fluorooctane sulfonamides/sulfonamidoethanols; High-volume air sampling; GC/PCI–MS; Isotope-labelled internal standards; Matrix effects

Determination of water-soluble and insoluble (dilute-HCl-extractable) fractions of Cd, Pb and Cu in Antarctic aerosol by square wave anodic stripping voltammetry: distribution and summer seasonal evolution at Terra Nova Bay (Victoria Land) by A. Annibaldi; C. Truzzi; S. Illuminati; E. Bassotti; G. Scarponi (pp. 977-998).

Eight PM10 aerosol samples were collected in the vicinity of the “Mario Zucchelli” Italian Antarctic Station (formerly Terra Nova Bay Station) during the 2000–2001 austral summer using a high-volume sampler and precleaned cellulose filters. The aerosol mass was determined by differential weighing of filters carried out in a clean chemistry laboratory under controlled temperature and humidity. A two-step sequential extraction procedure was used to separate the water-soluble and the insoluble (dilute-HCl-extractable) fractions. Cd, Pb and Cu were determined in the two fractions using an ultrasensitive square wave anodic stripping voltammetric (SWASV) procedure set up for and applied to aerosol samples for the first time. Total extractable metals showed maxima at midsummer for Cd and Pb and a less clear trend for Cu. In particular, particulate metal concentrations ranged as follows: Cd 0.84–9.2 μg g⁻¹ (average 4.7 μg g⁻¹), Pb 13.2–81 μg g⁻¹ (average 33 μg g⁻¹), Cu 126–628 μg g⁻¹ (average 378 μg g⁻¹). In terms of atmospheric concentration, the values were: Cd 0.55–6.3 pg m⁻³ (average 3.4 pg m⁻³), Pb 8.7–48 pg m⁻³ (average 24 pg m⁻³), Cu 75–365 pg m⁻³ (average 266 pg m⁻³). At the beginning of the season the three metals appear widely distributed in the insoluble (HCl-extractable) fraction (higher proportions for Cd and Pb, 90–100%, and lower for Cu, 70–90%) with maxima in the second half of December. The soluble fraction then increases, and at the end of the season Cd and Pb are approximately equidistributed between the two fractions, while for Cu the soluble fraction reaches its maximum level of 36%. Practically negligible contributions are estimated for crustal and sea-spray sources. Low but significant volcanic contributions are estimated for Cd and Pb (∼10% and ∼5%, respectively), while there is an evident although not quantified marine biogenic source, at least for Cd. The estimated natural contributions (possibly including the marine biogenic source) cannot account for the high fractions of the metal contents, particularly for Pb and Cu, and this suggests that pollution from long-range transport is the dominant source. Figure Aerosol sampling in Antarctica

Keywords: Antarctic aerosol; Heavy metals; Soluble/insoluble fractionation; Square wave anodic stripping voltammetry; Summer seasonal variation; Source identification

Monitoring of PAHs in air by collection on XAD-2 adsorbent then microwave-assisted thermal desorption coupled with headspace solid-phase microextraction and gas chromatography with mass spectrometric detection by Ming-Chi Wei; Wan-Ting Chang; Jen-Fon Jen (pp. 999-1005).

Microwave-assisted thermal desorption (MAD) coupled to headspace solid-phase microextraction (HS-SPME) has been studied for in-situ, one-step, sample preparation for PAHs collected on XAD-2 adsorbent, before gas chromatography with mass spectrometric detection. The PAHs on XAD-2 were desorbed into the extraction solution, evaporated into the headspace by use of microwave irradiation, and absorbed directly on a solid-phase microextraction fiber in the headspace. After desorption from the SPME fiber in the hot GC injection port, PAHs were analyzed by GC–MS. Conditions affecting extraction efficiency, for example extraction solution, addition of salt, stirring speed, SPME fiber coating, sampling temperature, microwave power and irradiation time, and desorption conditions were investigated. Experimental results indicated that extraction of 275 mg XAD-2, containing 10–200 ng PAHs, with 10-mL ethylene glycol–1 mol L⁻¹ NaCl solution, 7:3, by irradiation with 120 W for 40 min (the same as the extraction time), and collection with a PDMS–DVB fiber at 35 °C, resulted in the best extraction efficiency. Recovery was more than 80% and RSD was less than 14%. Optimum desorption was achieved by heating at 290 °C for 5 min. Detection limits varied from 0.02 to 1.0 ng for different PAHs. A real sample was obtained by using XAD-2 to collect smoke from indoor burning of joss sticks. The amounts of PAHs measured varied from 0.795 to 2.53 ng. The method is a simple and rapid procedure for determination of PAHs on XAD-2 absorbent, and is free from toxic organic solvents.

Keywords: PAHs; Microwave-assisted desorption; Headspace SPME

Selective solid-phase extraction of tebuconazole in biological and environmental samples using molecularly imprinted polymers by Mai-ling Hu; Ming Jiang; Peng Wang; Su-rong Mei; Yan-fei Lin; Xiao-zhong Hu; Yun Shi; Bin Lu; Kang Dai (pp. 1007-1016).

Molecularly imprinted polymers (MIPs) were prepared by precipitation polymerization using tebuconazole (TBZ) as a template. Frontal chromatography and selectivity experiments were used to determine the binding capabilities and binding specificities of different MIPs. The polymer that had the highest binding selectivity and capability was used as the solid-phase extraction (SPE) sorbent for the direct extraction of TBZ from different biological and environmental samples (cabbage, pannage, shrimp, orange juice and tap water). The extraction protocol was optimized and the optimum conditions were: conditioning with 5 mL methanol:acetic acid (9:1), 5 mL methanol and 5 mL water respectively, loading with 5 mL aqueous samples, washing with 1.2 mL acetonitrile (ACN):phosphate buffer (5:5, pH3), and eluting with 3 mL methanol. The MIPs were able to selectively recognize, effectively trap and preconcentrate TBZ over a concentration range of 0.5–15 μmol/L. The intraday and interday RSDs were less than 9.7% and 8.6%, respectively. The limit of quantification was 0.1 μmol/L. Under optimum conditions, the MISPE recoveries of spiked cabbage, pannage, shrimp, orange juice and tap water were 62.3%, 75.8%, 71.6%, 89% and 93.9%, respectively. MISPE gave better HPLC separation efficiencies and higher recoveries than C18 SPE and strong cation exchange (SCX) SPE. Figure HPLC analysis of spiked pannage after MISPE (A) and after C18 SPE (B). HQ (1), E3 (2), p-NP (3), FTF (4), TBZ (5), PNZ (6), HXZ (7)

Keywords: Molecularly imprinted polymers; Frontal chromatography; Solid-phase extraction; Tebuconazole; Biological and environmental samples

Application of hydrocyanic acid vapor generation via focused microwave radiation to the preparation of industrial effluent samples prior to free and total cyanide determinations by spectrophotometric flow injection analysis by Maria Cristina Baptista Quaresma; Maria de Fátima Batista de Carvalho; Francis Assis Meirelles; Vânia Maria Junqueira Santiago; Ricardo Erthal Santelli (pp. 1017-1025).

A sample preparation procedure for the quantitative determination of free and total cyanides in industrial effluents has been developed that involves hydrocyanic acid vapor generation via focused microwave radiation. Hydrocyanic acid vapor was generated from free cyanides using only 5 min of irradiation time (90 W power) and a purge time of 5 min. The HCN generated was absorbed into an accepting NaOH solution using very simple glassware apparatus that was appropriate for the microwave oven cavity. After that, the cyanide concentration was determined within 90 s using a well-known spectrophotometric flow injection analysis system. Total cyanide analysis required 15 min irradiation time (90 W power), as well as chemical conditions such as the presence of EDTA–acetate buffer solution or ascorbic acid, depending on the effluent to be analyzed (petroleum refinery or electroplating effluents, respectively). The detection limit was 0.018 mg CN l⁻¹ (quantification limit of 0.05 mg CN l⁻¹), and the measured RSD was better than 8% for ten independent analyses of effluent samples (1.4 mg l⁻¹ cyanide). The accuracy of the procedure was assessed via analyte spiking (with free and complex cyanides) and by performing an independent sample analysis based on the standard methodology recommended by the APHA for comparison. The sample preparation procedure takes only 10 min for free and 20 min for total cyanide, making this procedure much faster than traditional methodologies (conventional heating and distillation), which are time-consuming (they require at least 1 h). Samples from oil (sour and stripping tower bottom waters) and electroplating effluents were analyzed successfully.

Keywords: Cyanide; Industrial effluents; Microwave-assisted distillation; Cyanide metallic complex; Vapor generation

Determination of epoxides by high-performance liquid chromatography following derivatization with N,N-diethyldithiocarbamate by Catrina L. Dupard-Julien; Bhaskarachary Kandlakunta; Rao M. Uppu (pp. 1027-1032).

A reversed-phase, high-performance liquid chromatography (RP-HPLC) method that allows quantitation of low levels of epoxides has been described. The method involved derivatization of epoxides using 100- to 1,000-fold excess N,N-diethyldithiocarbamate (DTC) at 60 °C for 20 min at neutral pH. The unreacted DTC was then decomposed to CS₂ and diethyl amine by acidification of the reaction mixture to pH 2 using orthophosphoric acid. The first two steps could be performed in the same reaction vessel by sequential addition of reagents. In the final step, an aliquot (20 μL) of the derivatized sample was analyzed for the presence of stable esters of DTC by RP-HPLC using a Supelcosil LC-18-S (150 × 4.6-mm) column and a mobile phase consisting of 40% (v/v) acetonitrile in water at a flow of 1 mL min⁻¹. Using UV detection at 278 nm, the epoxides gave linear responses in the concentration range of 0.25 to 50 μM. The method is robust, and as low as 5 pmol of the analyte could be successfully detected and quantified with recoveries of ≥94%. Following a minimal pretreatment such as ultrafiltration (molecular weight cutoff 5,000 Da), the method is suitable for analysis of epoxides in complex physiological fluids (e.g., fetal bovine serum). The method has been rigorously evaluated and adapted in our laboratory for routine analysis and determination of stability of epoxides of 1,3-butadiene and other alkenes added to cell cultures.

Keywords: 1,3-Butadiene; Cell culture; N,N-Diethyldithiocarbamate; 1,2-Epoxy-3-butene; Quantitation of epoxides; Reversed-phase HPLC; Robustness

The potentiometric behavior of polymer-supported metallophthalocyanines used as anion-selective electrodes by M. Arvand; A. Pourhabib; R. Shemshadi; M. Giahi (pp. 1033-1039).

Liquid polymer membrane electrodes based on nickel and manganese phthalocyanines were examined for use as anion-selective electrodes. The electrodes were prepared by incorporating the ionophores into plasticized poly(vinyl chloride) membranes, which were directly coated onto the surfaces of graphite electrodes. The resulting electrodes demonstrate near-Nernstian responses over a wide linear range of perchlorate anion (5 × 10⁻⁷ to 1 × 10⁻¹ M). The electrodes have a fast response time, submicromolar detection limits (5 × 10⁻⁷ M perchlorate), and could be used over a wide pH range of 3.5–10. The influences of lipophilic cationic and anionic additives on the response properties of the electrodes were investigated. The proposed sensors revealed high selectivity for perchlorate over a number of common inorganic and organic anions. The highest selectivity was observed for the electrode based on manganese phthalocyanine in the presence of the lipophilic anionic additive sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate. Application of the electrodes to determine perchlorate in tap water and human urine is also reported.

Keywords: Anion-selective electrodes; Perchlorate ion; Nickel phthalocyanine; Manganese phthalocyanine; Potentiometry

An adaptive strategy for selecting representative calibration samples in the continuous wavelet domain for near-infrared spectral analysis by Da Chen; Wensheng Cai; Xueguang Shao (pp. 1041-1048).

Sample selection is often used to improve the cost-effectiveness of near-infrared (NIR) spectral analysis. When raw NIR spectra are used, however, it is not easy to select appropriate samples, because of background interference and noise. In this paper, a novel adaptive strategy based on selection of representative NIR spectra in the continuous wavelet transform (CWT) domain is described. After pretreatment with the CWT, an extension of the Kennard–Stone (EKS) algorithm was used to adaptively select the most representative NIR spectra, which were then submitted to expensive chemical measurement and multivariate calibration. With the samples selected, a PLS model was finally built for prediction. It is of great interest to find that selection of representative samples in the CWT domain, rather than raw spectra, not only effectively eliminates background interference and noise but also further reduces the number of samples required for a good calibration, resulting in a high-quality regression model that is similar to the model obtained by use of all the samples. The results indicate that the proposed method can effectively enhance the cost-effectiveness of NIR spectral analysis. The strategy proposed here can also be applied to different analytical data for multivariate calibration.

Keywords: Sample selection; Near-infrared spectroscopy; Continuous wavelet transform; Extension of the Kennard–Stone (EKS) algorithm

NADH screen-printed electrodes modified with zirconium phosphate, Meldola blue, and Reinecke salt. Application to the detection of glycerol by FIA by A. Radoi; D. Compagnone; M. Batič; J. Klinčar; Lo Gorton; G. Palleschi (pp. 1049-1058).

Bulk screen-printed electrodes (bSPEs) modified with zirconium phosphate (ZrP) and Meldola blue (MB) and by electrochemical deposition of a Reineckate film (bMBZrPRs-SPEs) have been constructed and used as NADH sensors. Cyclic voltammetric investigation of these bulk electrochemically modified screen-printed electrodes revealed stable catalytic activity in oxidation of the reduced form of the coenzyme nicotinamide adenine dinucleotide (NADH). Flow-injection analysis (FIA) coupled with amperometric detection confirmed the improved stability of the bMBZrPRs-SPEs (10⁻⁴ mol L⁻¹ NADH, %RSD = 4.2, n = 90, pH 7.0). Other conditions, for example applied working potential (+50 mV relative to Ag|AgCl), flow rate (0.30 mL min⁻¹) and pH-dependence (range 4.0–10.0) were evaluated and optimized. A glycerol biosensor, prepared by immobilizing glycerol dehydrogenase (GDH) on the working electrode area of a bMBZrPRs-SPE, was also assembled. The biosensor was most stable at pH 8.5 (%RSD = 5.6, n = 70, 0.25 mmol L⁻¹ glycerol). The detection and quantification limits were 2.8 × 10⁻⁶ and 9.4 × 10⁻⁶ mol L⁻¹, respectively, and the linear working range was between 1.0 × 10⁻⁵ and 1.0 × 10⁻⁴ mol L⁻¹. To assess the effect of interferences, and recovery by the probe we analyzed samples taken during fermentation of chemically defined grape juice medium and compared the results with those obtained by HPLC.

Keywords: Zirconium phosphate; Meldola blue; Reinecke salt; NADH; Glycerol biosensor

An amperometric acetylthiocholine sensor based on immobilization of acetylcholinesterase on a multiwall carbon nanotube–cross-linked chitosan composite by Dan Du; Xi Huang; Jie Cai; Aidong Zhang; Jiawang Ding; Shizhen Chen (pp. 1059-1065).

A simple method has been devised for immobilization of acetylcholinesterase (AChE)—covalent bonding to a multiwall carbon nanotube (MWNT)–cross-linked chitosan composite (CMC)—and a sensitive amperometric sensor for rapid detection of acetylthiocholine (ATCl) has been based on this. Fourier-transform infrared spectroscopy proved that the native structure of the immobilized enzyme was preserved on this chemically clean and homogeneous composite film, because of the excellent biocompatibility and non-toxicity of chitosan. Glutaraldehyde was used as cross-linker to covalently bond the AChE, and efficiently prevented leakage of the enzyme from the film. Because of the inherent conductive properties of the MWNT, the immobilized AChE had greater affinity for ATCl and excellent catalytic effect in the hydrolysis of ATCl, with a $$K^{{{ ext{app}}}}_{{ ext{m}}} $$ value of 132 μmol L⁻¹, forming thiocholine, which was then oxidized to produce a detectable and rapid response. Under optimum conditions the amperometric current increased linearly with the increasing concentration of ATCl in the range 2.0–400 μmol L⁻¹, with a detection limit of 0.10 μmol L⁻¹. Fabrication reproducibility of the sensor was good and the stability was acceptable. The sensor is a promising new tool for characterization of enzyme inhibitors and for pesticide analysis. Abstract

Keywords: Acetylthiocholine sensor; Acetylcholinesterase; Chitosan; Multiwall carbon nanotube; Composite film

Fluorescence sensor for water in organic solvents prepared from covalent immobilization of 4-morpholinyl-1, 8-naphthalimide by Cheng-Gang Niu; Pin-Zhu Qin; Guang-Ming Zeng; Xiao-Qin Gui; Ai-Ling Guan (pp. 1067-1074).

A new fluorescent dye, N-allyl-4-morpholinyl-1,8-naphthalimide (AMN), was synthesized as a fluorescence indicator in the fabrication of a sensor for determining water content in organic solvents. To prevent leakage of the fluorophore, AMN was photo-copolymerized with acrylamide, (2-hydroxyethyl)methacrylate, and triethylene glycol dimethacrylate on a glass surface treated with a silanizing agent. The sensing mechanism is based on the solvatochromic feature of the covalently immobilized AMN. The fluorescence intensity of AMN decreased with increasing water contents when it was excited at 400 nm. In the range of ca. 0.00–4.40% (v/v), the fluorescence intensity of AMN changed as a linear function of water content. The sensor exhibited satisfactory reproducibility, reversibility, and a response time (t ₉₉) of the order of 50 s. The detection limit was solvent-dependent, when acetonitrile was used as the solvent, and the detection limit could be as low as 0.006% (v/v) of water. Additionally, the prepared sensor is pH-insensitive and possesses a relatively long lifetime of at least one month.

Keywords: Fluorescence sensor; Covalent immobilization; N-Allyl-4-morpholinyl-1,8-naphthalimide; Water content

Amperometric hydrogen peroxide sensor based on a sol-gel-derived ceramic carbon composite electrode with toluidine blue covalently immobilized using 3-aminopropyltrimethoxysilane by K. Thenmozhi; S. Sriman Narayanan (pp. 1075-1082).

A carbon composite amperometric hydrogen peroxide sensor has been developed using a sol-gel technique. Toluidine blue (TB), which acts as the redox mediator, was covalently immobilized via glutaraldehyde crosslinking with an organically modified silane, namely 3-aminopropyltrimethoxysilane (APTMOS). Methyltrimethoxysilane (MTMOS) was used as the additional monomer; this controls the hydrophobicity of the electrode surface, thus limiting the wettability. The immobilization of TB within the sol-gel matrix was confirmed with FTIR studies. The sol-gel mixture containing TB immobilized in APTMOS and MTMOS was mixed with graphite powder in order to prepare the carbon composite electrode. The electrode was characterized using voltammetric techniques and its electrocatalytic activity for the reduction of hydrogen peroxide was also studied. The carbon composite electrode has the advantage of sensing H₂O₂ at a lower potential and with a higher sensitivity, and interferences due to ascorbic acid, uric acid and acetaminophen were greatly minimized. The linear range for the determination of H₂O₂ extends from 5.37 × 10⁻⁶ to 6.15 × 10⁻³ M, with a correlation coefficient of 0.9981. The detection limit was found to be 2.15 × 10⁻⁶ M. The covalent immobilization of TB effectively prevents the leakage of the water-soluble mediator during measurements. The modified electrode, aside from electrocatalyzing the reduction of H₂O₂, exhibits distinct advantages in terms of surface renewal in the event of surface fouling, as well as simple preparation, good chemical and mechanical stability, and good reproducibility. Figure Amperometric hydrogen peroxide sensor based on sol-gel-derived ceramic carbon composite electrode with toluidine blue covalently immobilized using 3-aminopropyltrimethoxysilane

Keywords: Sol-gel; Covalent immobilization; Toluidine blue; Amperometry; Hydrogen peroxide

Validation of a new planar chromatographic method for quantification of the heterocyclic aromatic amines most frequently found in meat by Ute Jautz; Gertrud Morlock (pp. 1083-1093).

A new HPTLC method, in which all the HPTLC steps are performed automatically, has been established for quantification of the five most frequently found heterocyclic aromatic amines (HAA: PhIP, MeIQx, 4,8-DiMeIQx, norharmane, and harmane). The method was used for trace analysis (low μg kg⁻¹ range) of HAA in meat samples and found to be a cost-effective alternative to HPLC, because it enables simultaneous chromatography of up to 20 samples within 30 min. After preconditioning of the HPTLC silica gel layer with ammonia vapour the plate was developed with methanol–chloroform, 1:9 (v/v). At least 4ó separations were obtained and selectivity for the meat matrix was achieved. In repeatability tests relative standard deviations (RSD, n = 14, peak height) were less than or equal to ±3.3%. In tests of intermediate precision (mean value for 14 tracks on six different plates on six different days) RSDs were better than ±2% (peak height). Measurement of the reproducibility of migration distances on six different plates resulted in RSDs less than or equal to ±1.3%. Limits of detection and quantification (S/N 3 and 10, respectively) for the five HAA ranged between 0.4 and 5 ng per band and between 0.8 and 14 ng per band, respectively. With paraffin–n-hexane, 3:7 (v/v), as fluorescence enhancer more sensitive determinations (up to 8.5-fold greater signal intensities) were achieved for PhIP, norharmane, and harmane. In the working range (1:10) polynomial regressions for PhIP, MeIQx, and 4,8-DiMeIQx and linear regressions for norharmane and harmane resulted in RSDs between ±1.9 and 3.6%. To confirm the absence of potentially coeluting minor HAA, rarely formed in meat, mass spectra were occasionally recorded by online ESI–MS. Robustness tests showed that preconditioning with ammonia was essential for successful separation and that relative humidity had only a minor effect on the chromatography. Analysis of HAA in a meat sample by HPTLC/UV-FLD and confirmation of MelQx by MS

Keywords: Planar chromatography; Method validation; Heterocyclic aromatic amines; HPTLC/UV–FLD–MS

Investigation of several parameters influencing signal generation in flow-through membrane-based enzyme immunoassay by Anna Yu. Kolosova; Sarah De Saeger; Sergei A. Eremin; Carlos Van Peteghem (pp. 1095-1104).

Rapid-response analytical tests that can be performed at the point of sampling are based on a visual detection system. The influence of different factors on the signal generation in a membrane-based enzyme immunoassay was investigated. The research was applied to a flow-through immunoassay for the detection of ochratoxin A (OTA). This assay format is a very convenient, simple and fast qualitative screening tool. Conjugates of OTA with horseradish peroxidase (HRP) and alkaline phosphatase (AP) were used as enzyme tracers. A new conjugate OTA-AP has been synthesized in our laboratory and its performance in the assay was compared with that of OTA-HRP. Different substrate systems for HRP and AP were compared. Several reagents, including polymers and surfactants, were tested for their possible effect on signal generation with the use of OTA-HRP conjugate. Polymers such as poly(vinyl alcohol) (PVA) and poly(ethylene glycol) (PEG) 6000 exerted a favourable effect on signal amplification, whereas surfactants negatively affected assay performance. The highest signal amplification (30–70% compared to the standard assay procedure) was achieved using 0.5% PVA in tetramethylbenzidine (TMB) Colorburst substrate solution and phosphate-buffered saline (PBS) for the washing step. It allowed more reliable visual estimation of the results from OTA-HRP assay. Exclusion of the detergent (Tween 20) from the washing solution exerted a favourable effect on assay performance using both enzyme tracers. The assay using OTA-HRP was more susceptible to matrix interferences than the assay with OTA-AP. Signal development in the matrix was better for the OTA-AP assay and visual estimation of the results was easier to perform in this case. For the analysis of spiked wheat samples, OTA-AP conjugate gave a more sensitive, stable and reproducible assay with a cut-off level of 4 μg kg⁻¹ for OTA. The application of the new OTA-AP conjugate resulted in improved assay performance for the food samples.

Keywords: Membrane-based enzyme immunoassay; Signal generation; Horseradish peroxidase; Alkaline phosphatase; Ochratoxin A

Quantification of Lactobacillus in fermented milk by multivariate image analysis with least-squares support-vector machines by Alessandra Borin; Marco Flôres Ferrão; Cesar Mello; Lívia Cordi; Luiz C. M. Pataca; Nelson Durán; Ronei J. Poppi (pp. 1105-1112).

This paper reports an approach for quantification of Lactobacillus in fermented milk, grown in a selective medium (MRS agar), by use of digital colour images of Petri plates easily obtained by use of a flatbed scanner. A one-dimensional data vector was formed to characterize each digital image on the basis of the frequency-distribution curves of the red (R), green (G), and blue (B) colour values, and quantities derived from them, for example lightness (L), relative red (RR), relative green (RG), and relative blue (RB). The frequency distributions of hue, saturation, and intensity (HSI) were also calculated and included in the data vector used to describe each image. Multivariate non-linear modelling using the least-squares support vector machine (LS-SVM) and a linear model based on PLS regression were developed to relate the microbiological count and the frequency vector. Feasibly models were developed using the LS-SVM and errors were below than 10% for Lactobacillus quantification, indicating the proposed approach can be used for automatic counting of colonies.

Keywords: Multivariate image analysis; Colour; Lactobacillus; Fermented milk; Least-squares support vector machines

Multivariate optimization of a microwave-assisted leaching procedure using dilute acid solutions, for FAAS determination of Cu, Fe, Mn, and Zn in multivitamin/multimineral supplements by Silvio Soriano; Annibal D. Pereira Netto; Ricardo J. Cassella (pp. 1113-1120).

This paper reports the development of a microwave-assisted procedure for leaching of copper, iron, manganese, and zinc from multivitamin/multimineral supplements by use of dilute acid before determination by flame atomic absorption spectrometry (FAAS). A Doehlert design was used to find optimum conditions for the procedure by use of response-surface methodology. Three variables (acid concentration in the leaching solution, irradiation time, and irradiation power) were used as factors in the optimization study for two acids, HCl and HNO₃. Final working conditions were established as a compromise between the optimum values for each analyte, taking into consideration the robustness of the procedure. The best leaching results were obtained with HNO₃ and the acid concentration, irradiation time, and irradiation power used were 0.70 mol L⁻¹, 15 min and 360 W, respectively. The accuracy of the optimized procedure was evaluated by comparison with a well-established closed-vessel microwave dissolution technique.

Keywords: Multivariate optimization; Doehlert matrix; Leaching; Flame atomic-absorption spectrometry

Filtration-based tyramide amplification technique—a new simple approach for rapid detection of aflatoxin B₁ by Debjani Saha; Debopam Acharya; Dipika Roy; Tarun K. Dhar (pp. 1121-1130).

The catalyzed reporter deposition (CARD) method of signal amplification, also called “tyramide signal amplification”, has been used in immunoassays not only to increase sensitivity but also to reduce assay time. The current approach to tyramide amplification in immunoassays involves slow incubation with agitation. In this paper we describe new filtration-based tyramide amplification and substrate visualization techniques. Compared with the standard method, this new approach greatly enhances spot intensities in membrane immunoassay and reduces biotinylated tyramide (B-T) and substrate consumption approximately fiftyfold, without loss of specificity. An improved test device and a cost-effective method for preparation of membranes for Super-CARD amplification have also been developed. The techniques have been used for rapid detection of aflatoxin B₁ (AFB₁) in a variety of foodstuffs with a detection limit of 12.5 μg kg⁻¹. The assay procedure involves sequential addition of standards or sample, AFB₁–horseradish peroxidase (HRP) conjugate, B-T, avidin–HRP, and substrate solution over anti-AFB₁ antibody-spotted zones of the membrane surface. The method saves time, improves reproducibility, eliminates many washing steps and avoids manipulation of the membranes between the different steps, while maintaining the sensitivity of the standard method. Average recoveries from different non-infected food samples spiked with AFB₁ at concentrations from 25 to 100 mg kg⁻¹ were between 95 and 105%. AFB₁ results obtained on different days for Aspergillus parasiticus infection of corn and groundnut samples correlated well with estimates obtained by HPLC. Figure The principle of filtration-based tyramide filtration technique

Keywords: Tyramide amplification; Super-CARD method; Aflatoxin B₁ ; Filtration-based amplification; Test device; Enhancement of spot intensity

Matrix-matched quantitative analysis of trace-elements in calcium carbonate shells by laser-ablation ICP–MS: application to the determination of daily scale profiles in scallop shell (Pecten maximus) by A. Barats; C. Pécheyran; D. Amouroux; S. Dubascoux; L. Chauvaud; O. F. X. Donard (pp. 1131-1140).

A micro-scale method has been developed for analysis of trace-element concentration profiles in the calcium carbonate shell of the Great Scallop (Pecten maximus). UV laser ablation at 266-nm coupled with ICP–MS detection was used to analyse daily calcite striae of shell samples to obtain high temporal resolution of trace element incorporation. Analysis of scallop shells was carefully examined to determine the quality of calcium carbonate ablation and calibration. An accurate external calibration method based on matrix matching was developed. Twelve sodium-free enriched calcium carbonate standards containing up to twenty-four elements were prepared, by co-precipitation with aqueous ammonia and NH₄HCO₃, and subsequently back-calibrated in the laboratory. These CaCO₃ standards were found to be homogenous and their use enabled sensitive quantitative analysis (detection limits of a few ng g⁻¹) over a wide range of concentrations (0.1 to 500 μg g⁻¹). Use of these CaCO₃ standards was also evaluated by analysis of three calcium-rich certified reference materials. Because calibration was consistent with the certified results, this analytical method is a sensitive tool for analysis of environmental calcium carbonate matrices. Repeated analysis of scallop shell samples collected simultaneously at the same location showed that the trace elements are homogeneously distributed along a stria. The reliability of such in-situ records of biogenic calcium carbonate (scallop shells) is apparent from the inter-individual and inter-annual reproducibility of the trace element profiles.

Keywords: Calcium carbonate; Matrix-matched standard; Laser ablation; ICP–MS; Scallop shell; Calibration; Trace elements

Sections

Personal tools

Analytical and Bioanalytical Chemistry (v.387, #3)

Sections

Personal tools

Local resources

Analytical and Bioanalytical Chemistry (v.387, #3)