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Analytical and Bioanalytical Chemistry (v.381, #3)

Degrees of difficulty by John Fetzer (pp. 527-528).

Analysis of biomaterials by Luigia Sabbatini (pp. 529-530).

Stenting: Biomaterials in mini-invasive cardiovascular applications by Marco Prunotto; Marco Galloni (pp. 531-533).

Phosphorylcholine-containing polymers for biomedical applications by Yasuhiko Iwasaki; Kazuhiko Ishihara (pp. 534-546).

Bulk and surface modifications of polylactide by Shenguo Wang; Wenjin Cui; Jianzhong Bei (pp. 547-556).

This article reviews various methods of modifying the bulk and surface properties of poly(lactic acid) (PLA) so that the polymer may be used as a drug carrier in a drug delivery system (DDS) and as a cell scaffold in tissue engineering. Copolymerization of lactide with other lactone-type monomers or monomers with functional groups such as malic acid, copolymerization of lactide with macromolecular monomer such as poly(ethylene glycol) (PEG) or dextran, as well as blending polylactide and natural derivatives and other methods of bulk modification are discussed. Surface modifications of PLA-type copolymers, such as surface coating, chemical modification, and plasma treatment are described. Cell culture technology proves the efficiency of bulk and surface modification and the potential application of PLA in tissue engineering.

Keywords: Polylactide; Bulk modification; Surface modification; Hydrophilicity; Cell affinity; Tissue engineering

Assessing the biocompatibility of NiTi shape memory alloys used for medical applications by Mohammed Es-Souni; Martha Es-Souni; Helge Fischer-Brandies (pp. 557-567).

The present paper reviews aspects related to the biocompatibility of NiTi shape memory alloys used for medical applications. These smart metallic materials, which are characterised by outstanding mechanical properties, have been gaining increasing importance over the last two decades in many minimal invasive surgery and diagnostic applications, as well as for other uses, such as in orthodontic appliances. Due to the presence of high amounts of Ni, the cytotoxicity of such alloys is under scrutiny. In this review paper we analyse work published on the biocompatibility of NiTi alloys, considering aspects related to: (1) corrosion properties and the different methods used to test them, as well as specimen surface states; (2) biocompatibility tests in vitro and in vivo; (3) the release of Ni ions. It is shown that NiTi shape memory alloys are generally characterised by good corrosion properties, in most cases superior to those of conventional stainless steel or Co–Cr–Mo-based biomedical materials. The majority of biocompatibility studies suggest that these alloys have low cytotoxicity (both in vitro and in vivo) as well as low genotoxicity. The release of Ni ions depends on the surface state and the surface chemistry. Smooth surfaces with well-controlled structures and chemistries of the outermost protective TiO₂ layer lead to negligible release of Ni ions, with concentrations below the normal human daily intake.

Keywords: NiTi shape memory alloys; Corrosion; Biocompatibility; Genotoxicity; Ni release

From biomimetic apatites to biologically inspired composites by A. Tampieri; G. Celotti; E. Landi (pp. 568-576).

Hydroxyapatite is an elective material for bone substitution. In this outline of our recent activity the crucial role of nanostructured ceramics in the design and preparation of ceramic scaffolds will be described, focussing on our more recent interest in biomimetic apatites, in particular apatites containing HPO₄²⁻ CO₃²⁻ and Mg²⁺ which are similar to the mineral component of bone. The paper describes such nanostructured products and, in particular, innovative synthetic techniques capable of yielding powders with higher reactivity and bioactivity. However, so far the characteristics of artificial bone tissues have been shown to be very different from those of natural bone, mainly because of the absence of the peculiar self-organizing interaction between apatites and the protein component. This causes modification of the structure of apatites and of the features of the overall composite forming human bone tissue. Therefore, attempts to mimic the features and structure of natural bone tissue, leading toward so-called bio-inspired materials, will be speculated upon. New techniques used to reproduce a composite in which a nanosize blade-like crystal of hydroxyapatite (HA) grows in contact with self-assembling fibres of natural polymer will be presented. In this specific case, the amazing ability of biological systems to store and process information at the molecular level, nucleating nanosize apatites (bio-inspired material), is exploited.

Keywords: Bone substitute; Biomimetic apatites; Biohybrid composite; Biologically inspired synthesis

Raman piezo-spectroscopic analysis of natural and synthetic biomaterials by Giuseppe Pezzotti (pp. 577-590).

Raman piezo-spectroscopy of bone, teeth, and artificial joints is reviewed with emphasis placed on confocal microprobe techniques. Characteristic spectra are presented and quantitative assessments of their phase structure and stress dependence are shown. Vibrational spectroscopy is used here to study the microscopic stress response of cortical bone to external stress (with or without internal damages), to define microscopic stresses across the dentine–enamel junction under increasing external compressive load, and to characterize interactions between prosthetic implants and biological environment. Confocal spectroscopy allows acquisition of spatially resolved spectra and stress imaging with high spatial resolution.

Keywords: Biomaterials; Piezo-spectroscopy; Microstress; Bone; Teeth; Artificial joints

Recent advances in microcontact printing by Arjan P. Quist; Elisabeth Pavlovic; Sven Oscarsson (pp. 591-600).

Microcontact printing is a remarkable surface patterning technique. Developed about 10 years ago, it has triggered enormous interest from the surface science community, as well as from engineers and biologists. The last five years have been rich in improvements to the microcontact printing process itself, as well as in new technical innovations, many designed to suit new applications. In this review, we describe the evolution of microcontact printing over the past five years. The review is categorized into three main sections: the improvements made to the technique, new variations, and new applications.

Keywords: Microcontact printing; PDMS; Polydimethylsiloxane; Surface patterning; Self-assembled monolayers; Soft lithography

Silica xerogels as a delivery system for the controlled release of different molecular weight heparins by N. Roveri; M. Morpurgo; B. Palazzo; B. Parma; L. Vivi (pp. 601-606).

In this work, we investigated a sol–gel derived silica matrix as a delivery system for the prolonged release of different molecular weight heparins, which allows the glycosaminoglicons to retain their whole biological activity. Several xerogels were obtained by embedding different molecular weight heparins into matrices prepared by using different amount of NH₄OH as a catalyst during gel formation. Gel synthesis parameters, drug release properties, and xerogels surface area were evaluated. Unfractionated, low and oligo-molecular weight heparins were embedded into xerogels and the effect of the molecular weight on the release kinetics and the retained biological activity has been investigated. The results show that the surface area of the matrix is a determinant parameter affecting drug release kinetics. This structural feature can be modified by varying the catalyst tetraethoxysilane molar ratio used during the matrix synthesis. In most cases release kinetics fitted the Higuchi diffusive model and a lower diffusion rate was observed from silica matrices characterized by a smaller surface area. In the case of matrices with lower surface area, loaded with unfractionated heparin, zero order kinetics was observed. In this paper, we have defined a heparin release silica xerogel system and we have pointed out how modulation of its synthesis parameters allows adjusting the release of heparin according to therapeutic needs.

Keywords: Silica xerogel; Heparins; Bioactive material; Controlled release material; Biomaterial

Analytical characterization of bioactive fluoropolymer ultra-thin coatings modified by copper nanoparticles by N. Cioffi; N. Ditaranto; L. Torsi; R. A. Picca; L. Sabbatini; A. Valentini; L. Novello; G. Tantillo; T. Bleve-Zacheo; P. G. Zambonin (pp. 607-616).

Copper–fluoropolymer (Cu-CFx) nano-composite films are deposited by dual ion-beam sputtering. The extensive analytical characterization of these layers reveals that inorganic nanoparticles composed of Cu(II) species are evenly dispersed in a branched fluoropolymer matrix. In particular, X-ray photoelectron spectroscopy has been employed to study the surface chemical composition of the material and to assess how it changes on increasing the copper loading in the composite. Transmission electron microscopy reveals that the copper nanoclusters have a mean diameter of 2–3 nm and are homogeneously in-plane distributed in the composite films. Electrothermal atomic absorption spectroscopy has been used to study the kinetics of copper release in the solutions employed for the biological tests. The Cu-CFx layers are employed as bioactive coatings capable of inhibiting the growth of target microorganisms such as Saccharomyces cerevisiae, Escherichia coli, Staphylococcus aureus, and Lysteria. The results of the analytical characterization enable a strict correlation to be established among the chemical composition of the material surface, the concentration of copper dissolved in the microorganisms broths, and the bioactivity of the nano-structured layer.

Keywords: Bioactive; Fluoropolymer; IBS; Nanocomposite; Nanoparticle; XPS

Corrosion resistance and bioactivity of titanium after surface treatment by three different methods: ion implantation, alkaline treatment and anodic oxidation by D. Krupa; J. Baszkiewicz; J. A. Kozubowski; J. Mizera; A. Barcz; J. W. Sobczak; A. Biliński; B. Rajchel (pp. 617-625).

The paper compares the effects of various surface modifications, ion implantation, alkaline treatment and anodic oxidation, upon the corrosion resistance and bioactivity of titanium. The chemical composition of the surface layers thus produced was determined by XPS, SIMS and EDS coupled with SEM. The structure of the layers was examined by TEM, and their phase composition by XRD. The corrosion resistance was determined by electrochemical methods after the samples were exposed to the test conditions for 13 h. The bioactivity of titanium was evaluated in a simulated body fluid at a temperature of 37°C after various exposure time.

Keywords: Titanium; Surface modification; Corrosion resistance; Bioactivity

Electrosynthesis and analytical characterization of PMMA coatings on titanium substrates as barriers against ion release by E. De Giglio; S. Cometa; L. Sabbatini; P. G. Zambonin; G. Spoto (pp. 626-633).

The performance of polyacrylic coatings as barrier films against corrosion of titanium-based orthopaedic implants was investigated. In particular, poly(methyl methacrylate) (PMMA) was electrosynthesized on titanium substrates by electro-reductive processes from aqueous monomer solutions. The obtained PMMA coatings were characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The effect of an annealing treatment on the morphology of coatings with respect to uniformity and porosity of films was assessed by scanning electron microscopy (SEM). An inductively coupled plasma-mass spectrometry (ICP-MS) technique was used for ion concentration measurements in ion release tests performed on TiAlV sheets modified with PMMA coatings (annealed and unannealed). Results indicated that the annealing process produces coatings with considerable anticorrosion performances.

Keywords: PMMA; Electrosynthesis; XPS; Titanium; Ion release; Biomaterial

Physical and chemical aspects of a new porous hydroxyapatite by R. Martinetti; L. Dolcini; C. Mangano (pp. 634-638).

The new engineered porous hydroxyapatite (EP-HA) described in this paper seems to be suitable as a bone substitute. Its physico-chemical characteristics and morphology are similar to those of natural bone. Study of its histological behaviour in humans revealed bone formation within and around the porous hydroxyapatite that is markedly resorbed.

Keywords: Bone repair; Hydroxyapatite; Porosity

Biocompatible channels for field-flow fractionation of biological samples: correlation between surface composition and operating performance by Barbara Roda; Nicola Cioffi; Nicoletta Ditaranto; Andrea Zattoni; Sonia Casolari; Dora Melucci; Pierluigi Reschiglian; Luigia Sabbatini; Antonio Valentini; Pier Giorgio Zambonin (pp. 639-646).

Biocompatible methods capable of rapid purification and fractionation of analytes from complex natural matrices are increasingly in demand, particularly at the forefront of biotechnological applications. Field-flow fractionation is a separation technique suitable for nano-sized and micro-sized analytes among which bioanalytes are an important family. The objective of this preliminary study is to start a more general approach to field-flow fractionation for bio-samples by investigation of the correlation between channel surface composition and biosample adhesion. For the first time we report on the use of X-ray photoelectron spectroscopy (XPS) to study the surface properties of channels of known performance. By XPS, a polar hydrophobic environment was found on PVC material commonly used as accumulation wall in gravitational field-flow fractionation (GrFFF), which explains the low recovery obtained when GrFFF was used to fractionate a biological sample such as Staphylococcus aureus. An increase in separation performance was obtained first by conditioning the accumulation wall with bovine serum albumin and then by using the ion-beam sputtering technique to cover the GrFFF channel surface with a controlled inert film. XPS analysis was also employed to determine the composition of membranes used in hollow-fiber flow field-flow fractionation (HF FlFFF). The results obtained revealed homogeneous composition along the HF FlFFF channel both before and after its use for fractionation of an intact protein such as ferritin.

Keywords: Field-flow fractionation (FFF); X-ray photoelectron spectroscopy (XPS); Ion-beam sputtering (IBS); Gravitational FFF (GrFFF); Hollow-fiber flow FFF (HF FlFFF)

Systematic development of an enzymatic phosphorylation assay compatible with mass spectrometric detection by A. R. de Boer; T. Letzel; H. Lingeman; H. Irth (pp. 647-655).

The enzymatic peptide phosphorylation by cAMP-dependent protein kinase A (PKA) was optimized and monitored by means of electrospray ionization mass spectrometry (ESI-MS). The direct detection of phosphorylated peptides by MS renders labeling unnecessary, reduces time and labor, due to less initial sample pretreatment. In this study the phosphorylation of the peptide malantide by PKA was performed in batch and reaction compounds were detected by ESI-MS after the incubation time. The subsequent product quantitation was accomplished by using one-point normalization. Applying this set-up, optimum solvent conditions (such as salt and modifier content), concentrations of essential reaction compounds (such as cAMP, Mg²⁺ and ATP), and the influence of reaction properties (such as pH and reaction time) were determined. The reaction milieu has to be suitable for both, the enzymatic reaction and the mass spectrometric detection. We found that the modifier content and the pH value had to be changed after the enzymatic reaction occurred. Through the addition of methanol and acetic acid, the reaction stopped immediately and a more sensitive mass spectrometric detection could be obtained simultaneously. Furthermore, an inhibitor study was performed, testing the inhibition potency of three protein kinase A inhibitors (PKIs). IC₅₀ values were determined and used to calculate the K _i values, that were 7.4, 19.0 and 340.0 nmol/L for PKI(6-22)amide, PKI(5-24)amide, and PKI(14-24)amide, respectively. These data vary between factor 4.4 (for PKI(6-22)amide) and 8.3 (for PKI(5-24)amide) compared to the K _i values described in literature. However, the K _i values are in good agreement with the data mainly obtained by fluorescence- or radioactivity-based methods. Nevertheless, our results indicate that ESI-MS is a realistic alternative to radioactivity and fluorescence detection in determining enzymatic activity. Furthermore we were able to illustrate its high potential as a quantitative detection method.

Keywords: ESI-MS; Mass spectrometry; PKA; Peptide phosphorylation; Inhibition reaction; Quantitative analysis

Fully automated in-tube solid-phase microextraction for liquid samples coupled to gas chromatography by Daniel Globig; Christian Weickhardt (pp. 656-659).

An online device is described in which analytes are extracted from a liquid sample by means of in-tube solid-phase microextraction (in-tube SPME), pulse released by rapid heating, and transferred to a gas chromatograph in a fully automated way. Switching of the sample and gas flows as well as the heating of the extraction tube and the valves is controlled by a remote computer system. Results obtained for river water and for aqueous standard solutions of phenanthrene are presented and are compared to the performance of standard SPME.

Keywords: Solid-phase microextraction; In-tube SPME; Automation; Gas chromatography

Screening populations of individual cells for secretory heterogeneity by Craig A. Aspinwall; Edward S. Yeung (pp. 660-666).

Many common metabolic and neurological disorders are related to defective regulation of exocytosis at the level of single cells. In exocytosis, vesicles containing the secretory product of a given cell type fuse with the plasma membrane allowing release of the vesicular contents into the extracellular environment where the physiological action can be exerted. The typical secretory vesicle contains between 0.15 and 10 attomoles of material that is released on a millisecond timescale. Hence, detection of this process presents several chemical and analytical challenges. In this work, we utilize the native ATP, stored at high concentrations within the secretory vesicles of most neuroendocrine cells and co-released during exocytosis and during cell lysis, as a universal tracer of cellular secretion events. Organisms studied include pancreatic islets, mast cells, and Escherischia coli. Cellular processes investigated include exocytotic release, stimulated cell lysis, and programmed cell lysis.

Keywords: Imaging; Cells; Bioanalysis; Chemiluminescence

Surface plasmon resonance-based immunoassay for 17β-estradiol and its application to the measurement of estrogen receptor-binding activity by Masahiro Miyashita; Takahiro Shimada; Hisashi Miyagawa; Miki Akamatsu (pp. 667-673).

A rapid and simple surface plasmon resonance (SPR)-based immunoassay for detection of 17β-estradiol was developed. The assay was designed as an inhibitive format, in which 17β-estradiol–BSA conjugates are immobilized on an SPR sensor chip and the binding of antibody to the chip is measured. The binding was inhibited by 17β-estradiol in the concentration range 0.468 to 21.4 nmol L⁻¹ with an IC₅₀ value of 2.29±0.10 nmol L⁻¹. Although not as sensitive as traditional radioimmunoassay (RIA) and enzyme-linked immunoassay (ELISA), this method requires no separation and washing after addition of the antibody, steps which are relatively time-consuming. Estrogen receptor (ER)-binding was then investigated using this SPR immunoassay for the determination of the amount of unbound 17β-estradiol after competition with test compounds for the ER-binding. Inhibition of the binding of 17β-estradiol to ER by diethylstilbestrol (DES) was successfully measured by injecting the reaction mixture into the SPR sensor after addition of the antibody. This binding assay requires no separation of unbound 17β-estradiol from the mixture and no radioisotope- or fluorescence-labeling of 17β-estradiol. These results show the potential usefulness of the SPR sensor both detecting 17β-estradiol and evaluating the ER-binding activity of xenoestrogens such as DES in a single assay system.

Keywords: 17β-Estradiol; Surface plasmon resonance sensor; Immunoassay; Estrogen receptor binding; Endocrine-disrupting chemicals

Novel potentiometric immunosensor for determination of diphtheria antigen based on compound nanoparticles and bilayer two-dimensional sol–gel as matrices by Dianping Tang; Ruo Yuan; Yaqin Chai; Yan Liu; Jianyuan Dai; Xia Zhong (pp. 674-680).

A novel method for fabrication of a diphtheria potentiometric immunosensor has been developed by means of self-assembling compound nanoparticles to a thiol-containing sol–gel network. A cleaned gold electrode was first immersed in a 3-mercaptopropyltrimethoxysilane (MPS) sol–gel solution to assemble a silica sol–gel monolayer. The silane entities were then polymerized into a two-dimensional sol–gel network (2D network) by dipping into aqueous NaOH. The second silane layer was formed by re-immersion in the MPS sol–gel solution overnight. The compound nanoparticles (nanocompounds) containing gold nanoparticles and silver nanoparticles were then chemisorbed on to the thiol groups of the second silane layer. Finally, diphtheria antibody (anti-Diph) was adsorbed on to the surface of the compound nanoparticles. The modified process was characterized by cyclic voltammetry (CV). Detection is based on the change in the potentiometric response before and after the antigen–antibody reaction. A direct potentiometric response to diphtheria antigen (Diph) was obtained from the immobilized diphtheria antibody. The potentiometric response of the resulting immunosensor was rapid and the linear range was from 22 to 800 ng mL⁻¹ with the linear regression equation ΔE=−79.5+69.4 log [Diph] and a detection limit of 3.7 ng mL⁻¹ (at 3δ). Up to 19 successive assay cycles with retention of sensitivity were achieved for probes regenerated with 0.2 mol L⁻¹ glycine–hydrochloric acid (Gly–HCl) buffer solution. Moreover, analytical results from several serum samples obtained using the developed technique were in satisfactory agreement with those given by the ELISA method, implying a promising alternative approach for detecting diphtheria antigen in clinical diagnosis.

Keywords: Compound nanoparticles; Potentiometric immunosensor; Diphtheria; Sol–gel

Determination of N-nitrosodiethanolamine in cosmetic products by LC–MS–MS by R. C. Schothorst; H. H. J. Somers (pp. 681-685).

We have developed and validated in-house a liquid chromatography and mass spectrometry (LC–MS–MS) method for determination of N-nitrosodiethanolamine (NDELA) in cosmetics. The sample is diluted with water and then a C₁₈ clean-up is performed. The average recovery of NDELA is 88.3%, range 48.3–112.7%, and the limit of detection is 22.8 μg kg⁻¹. The repeatability is 7.6%, and the intermediate precision is 8.7%. Surveys were carried out in the Netherlands in September and October 2002 to determine the quantities of NDELA in cosmetics marketed in the Netherlands. The LC–MS–MS method was used to determine the NDELA content of 140 cosmetic products including shower gels, hair oils, shampoos and conditioners, cream and foam baths, mud baths, scrubs, crème and other soaps, and body washes. NDELA at levels ranging from 23 to 992 μg kg⁻¹ was found in 35 cosmetic products.

Keywords: LC–MS–MS; Cosmetics; NDELAN-nitrosamine; The Netherlands

Development and application of a simple routine method for the determination of selenium in serum by octopole reaction system ICPMS by Stefan Stürup; Richard B. Hayes; Ulrike Peters (pp. 686-694).

The aim of the study was to develop an inductively coupled plasma mass spectrometry (ICPMS) method for robust and simple routine determination of selenium in serum. Polyatomic interferences on ⁷⁶Se, ⁷⁷Se, and ⁷⁸Se were removed by applying an octopole reaction system ICPMS with the reaction cell pressurized with H₂ gas. We developed a novel simple optimization routine for the H₂ gas flow based on a signal-to-noise ratio (SNR) calculation of the selenium signal measured in a single selenium standard. The optimum H₂ flow was 2.9 mL min⁻¹. The selenium content in serum was determined after a 50-fold dilution with 0.16 M HNO₃ and quantified by using addition calibration and gallium as an internal standard. The method detection limit was 0.10 μg L⁻¹ for ⁷⁶Se and ⁷⁸Se and 0.13 μg L⁻¹ for ⁷⁷Se. Human serum samples from a case-control study investigating if selenium was associated with risk of colorectal adenoma were analyzed. The average selenium concentration for the control group (n=768) was 137.1 μg L⁻¹ and the range was 73.4–305.5 μg L⁻¹. The within-batch repeatability (a batch is ten samples) estimated from 182 replicate analyses was 6.3% coefficient of variation (CV), whereas the between-batch repeatability was 7.4% CV estimated from 361 replicates between batches. The method accuracy was evaluated by analysis of a human serum certified reference material (Seronorm Serum level II, Sero A/S, Norway). There was a fairly good agreement between the measured average of 145±3 μg L⁻¹ (n=36) and the certified value of 136±9 μg L⁻¹. In addition the method was successfully applied for analysis of zinc serum concentrations without further optimization. For the Seronorm certified reference material a value of 911±75 μg L⁻¹ (n=31) for zinc was obtained, which corresponds well to the certified zinc value of 920±60 μg L⁻¹.

Keywords: ICPMS; Selenium; Serum; Octopole reaction system; Signal-to-noise optimization; Interferences

Determination of pesticides and PCBs in honey by solid-phase extraction cleanup followed by gas chromatography with electron-capture and nitrogen–phosphorus detection by A. Herrera; C. Pérez-Arquillué; P. Conchello; S. Bayarri; R. Lázaro; C. Yagüe; A. Ariño (pp. 695-701).

A multiresidue method for determination of 15 organochlorine pesticides (OCPs), six polychlorinated biphenyls (PCBs), and seven organophosphorus pesticides (OPPs) is implemented for routine determinations of residues in honey. The method involves solid-phase extraction cleanup and determination by GC–ECD/NPD. Quantitation limits ranged from 0.1 to 0.6 μg kg⁻¹ honey for OCPs and PCBs, and from 5.0 to 25.0 μg kg⁻¹ honey for OPPs. Recoveries of OCPs ranged between 77.4 and 94.0%; for PCBs they were from 63.8 to 73.5%. Recovery assays for OPPs varied from 66.7 to 98.1%. The method was applied to the analysis of 111 honey samples from Aragón, Spain. The results obtained indicated a low level of contamination by pesticide residues and PCBs, which can contribute to ensuring the consumer has a safe wholesome supply of honey.

Keywords: Honey; Solid-phase extraction (SPE); Gas chromatography (GC); Pesticides; Polychlorinated biphenyls

Concept and validation of a novel approach for producing large batches of reference material of ambient aerosols on filters by K. Wittmaack (pp. 702-712).

A novel method for preparing reference material of aerosol particulate matter (PM) on filters was developed by using the concept of very high volume, multiport sampling, and this was subsequently applied to produce more than 300 well-characterised units. The dedicated sampler built for this purpose features a 0.94-m-diameter, vacuum-tight main chamber with a total of 349 monitor ports, each holding a 37-mm-diameter, cellulose acetate–nitrate ester (CA) membrane filter with a nominal pore size of 0.8 μm. At a pressure difference of about 130 hPa across the filter cassettes, the total initial air flow rate was 350 m³ h⁻¹ (1.0 m³ h⁻¹ per filter). Investigations into the variability of filter parameters showed that the flow resistance of CA filters is mostly determined by and proportional to their blank mass, with a mean uncertainty of about 5%. Total suspended particulate matter (TSP) was sampled for a total of 50 h using 349 selected filters with a relatively narrow spread in blank mass. The mean TSP mass per filter thus produced was 3.35 mg. Corrected for small differences in blank mass of the filters, the normalised aerosol masses per filter of 96% of the samples exhibited normal distributions with standard deviations of only 2.1 and 3.4%, depending on details of the normalisation procedure. Within the limits of the technique, a variation of aerosol mass with radial distance from the centre of the sampler is not clearly evident. The results provide evidence that the multiport approach allows large batches of particulate matter on filters to be produced in a reliable manner.

Keywords: Aerosol; High-volume sampling; Reference material; Multiport sampler; Membrane filter

Direct and rapid analysis of ambient air and exhaled air via electrostatic precipitation of aerosols in an atomizer furnace and Zeeman spectrometry by A. A. Ivanenko; N. B. Ivanenko; M. A. Kuzmenkov; E. M. Jakovleva; A. Skudra; M. N. Slyadnev; A. A. Ganeev (pp. 713-720).

Techniques that allow the elements present in the air to be determined in a simple and rapid manner are very attractive. Direct aerosol sampling techniques avoid the need to pretreat the filter via wet digestion in order to remove any sources of contamination, and they decrease the precipitation time significantly. Analyzers based on this technique can also determine the concentrations of elements in the air automatically in situ. This paper is concerned with the development of a novel analytical system that is based on electrostatically precipitating aerosols from the air into a graphite furnace. The equipment includes a Zeeman spectrometer with high frequency modulation polarization (MGA-915), and an electrostatic precipitation system incorporated into the analyzer. The high sensitivity of the system developed here means that it can be used to determine element concentrations in the air exhaled by humans, as well as those in ambient air.

Keywords: Atomic absorption; Air; Exhaled air and aerosols

Particle-size distribution of polycyclic aromatic hydrocarbons in urban air in southern Spain by A. Gutiérrez-Dabán; A. J. Fernández-Espinosa; M. Ternero-Rodríguez; F. Fernández-Álvarez (pp. 721-736).

The size distribution of polycyclic aromatic hydrocarbons (PAH) was determined for airborne particles from a large city with high vehicular traffic. The analytical method was optimised and validated using NIST standard reference material (SRM 1649a Urban Dust). The 16 priority PAH listed in the US-EPA were Soxhlet-extracted from filtered particulate matter and then fractionated using on-column chromatography. The aromatic fraction was quantified by gas chromatography-mass spectrometry. Real samples of particles collected in Seville (Spain) were analysed using the validated method. Values for the total concentration of PAH in the air, as well as the concentrations of each PAH in six particle-size ranges were obtained. Values of the PAH in TSP, PM₁₀, PM_2.5 and PM₁ were assessed.

Keywords: Polycyclic aromatic hydrocarbons; Benzo[a]pyrene; Urban airborne particles; Size distribution; SRM 1649a

Isolation of selenium organic species from antarctic krill after enzymatic hydrolysis by Mariana Siwek; Boris Galunsky; Bernd Niemeyer (pp. 737-741).

Total selenium content and its distribution in the soluble and insoluble protein-bound fractions obtained after aqueous extraction of antarctic krill samples were determined. About 26% of the total selenium (2.4 μg g⁻¹ dry weight) was found in the supernatant; the rest was in the pellet. Isolation of low molecular selenium-containing fractions was also performed by enzymatic digestion of the protein, followed by size-exclusion chromatography in conjunction with atomic absorption spectrometry. From the applied various proteinases (pronase E, subtilisin Carlsberg, trypsin, chymotrypsin, proteinase and proteinase N from Bacillus subtilis and Novo 0.6 MPX enzyme), the treatment with pronase E led to best recovery of selenium. About 96% of the total Se was found in the hydrolysate, mainly in low molecular weight fractions. Eighty percent of the Se species were in fractions with molecular weights in the range of amino acids and short peptides. High-performance liquid chromatography/inductively coupled plasma mass spectrometry (HPLC-ICP-MS) allowed the identification of selenomethionine and the assumption that selenocystine or its derivatives were the main species in these fractions.

Keywords: Antarctic krill; Enzymatic digestion; HPLC-ICP-MS; Selenium organic compounds; Size-exclusion chromatography

A dynamic dilution system-based evaluation of the procedure adopted for determining ozone precursor volatile compounds by Fabienne Palluau; Philippe Mirabel; Maurice Millet (pp. 742-761).

A dynamic dilution system was created to evaluate the performance and the reliability of ozone precursor volatile organic compound (VOC) sampling (“TO-Can” canisters) and analysis (thermal desorption/gas chromatography/flame ionisation detection) techniques used by the “Laboratoire Interrégional de Chimie du Grand Est (LIC)”. Different atmospheres of VOCs were generated at concentrations between 0.8 and 25 ppb, with temperatures of 0, 10, 20 and 30 °C, and with relative humidities of 0, 30, 50, 70 and 90%. These conditions are generally representative of those commonly observed in ambient air in the eastern France. This dynamic dilution allows the simulation of a wide range of scenarios (concentrations, temperatures and relative humidities). After assessing the capacity and performance of the system, it was applied in order to evaluate the recoveries and stabilities of VOCs from canisters used for the collection and analysis of two mixtures of VOCs. The first mixture contained six alkanes (ethane, propane, butane, pentane, hexane and heptane), and the second contained five alkenes (ethene, propene, butene, 1-pentene and 1-hexene), five aromatics (benzene, toluene, ethylbenzene, m-xylene and o-xylene), acetylene, and 1,3-butadiene. No significant losses of alkanes from the canisters were observed after 21 days of storage, and good recoveries of alkanes from the canisters (>80%) were obtained regardless of the concentration, the temperature and the relative humidity. However, losses of certain aromatics were noted at low relative humidity.

Keywords: Ozone precursor VOCs; TO-Can Canisters; Thermal desorption (TD); Gas chromatography (GC); Flame ionisation detection (FID); Dynamic dilution system

Electrochemical characteristics of a platinum electrode modified with a matrix of polyvinyl butyral and colloidal Ag containing immobilized horseradish peroxidase by Ruo Yuan; Yan Liu; Qun-Fang Li; Ya-Qin Chai; Chang-Li Mo; Xia Zhong; Dian-Ping Tang; Jian-Yuan Dai (pp. 762-768).

A new hydrogen peroxide biosensor was constructed, which consisted of a platinum electrode modified by a matrix of polyvinyl butyral (PVB) and nanometer-sized Ag colloid containing immobilized horseradish peroxidase (HRP), and using Co(bpy)₃³⁺ as mediator in the hydrogen peroxide solution. The electrochemical characteristics of the biosensor were studied by cyclic voltammetry and chronoamperometry. The modified process was characterized by electrochemical impedance spectroscopy and cyclic voltammetry. The HRP immobilized on colloidal Ag was stable and retained its biological activity. The sensor displays excellent electrocatalytic response to the reduction of H₂O₂. Analytical parameters such as pH and temperature were also studied. Linear calibration for H₂O₂ was obtained in the range of 1×10⁻⁵ to 1×10⁻² M under optimized conditions. The sensor was highly sensitive to H₂O₂, with a detection limit of 2×10⁻⁶ M, and the sensor achieved 95% of steady-state current within 10 s. The sensor exhibited high sensitivity, selectivity and stability.

Keywords: Biosensor; Horseradish peroxidase; Cyclic voltammetry; Hydrogen peroxide; Ag colloid

Fabrication of a novel Li_xMoO_y film modified electrode and its application as an electrochemical sensor of iodate by Li Tian; Li Chen; Li Liu; Nan Lu; Hongding Xu (pp. 769-774).

A novel organic gel film modified electrode was simply and conveniently fabricated by casting Li_xMoO_y and polypropylene carbonate (PPC) onto the surface of a gold electrode. The cyclic voltammetry and amperometry studies demonstrated that the Li_xMoO_y film modified electrode has a high stability and a good electrocatalytic activity for the reduction of iodate. In amperometry, a good linear relationship between the steady current and the concentration of iodate was obtained in the range from 3×10⁻⁷ to 1×10⁻⁴ mol L⁻¹ with a correlation coefficient of 0.9997 and a detection limit of 1×10⁻⁷ mol L⁻¹.

Keywords: Li_xMoO_yPolypropylene carbonate; Electrocatalysis; Iodate

Microquantitative determination of hesperidin by pulse perturbation of the oscillatory reaction system by Nataša Pejić; Slavica Blagojević; Slobodan Anić; Vladana Vukojević; Ljiljana Kolar-Anić (pp. 775-780).

A simple and reliable kinetic method for the determination of hesperidin (Hesp) is developed. It is based on potentiometric monitoring of the concentration perturbations of the matrix reaction system which is in a stable non-equilibrium stationary state close to the bifurcation point. The Bray–Liebhafsky oscillatory reaction is used as the matrix system. The response of the matrix to perturbations by different concentrations of Hesp is followed by using a Pt electrode. A linear relationship between maximal potential shift and the logarithm of Hesp concentrations is obtained between 7.5 and 599.4 μg mL⁻¹. The limit of detection is 0.65 μg mL⁻¹. The described procedure has been successfully applied to the determination of Hesp from different sources (capsules, industrial and hand-squeezed orange juice, and white wine).

Keywords: Determination of hesperidin; Microquantitative analysis; Flavonoids; Perturbation technique; Bray–Liebhafsky oscillatory reaction

A novel salicylate-selective electrode based on a Sn(IV) complex of salicylal-imino acid Schiff base by Lan Xu; Ruo Yuan; Ya-Qin Chai; Xiu-Ling Wang (pp. 781-787).

A novel poly(vinyl chloride) membrane electrode with high selectivity toward salicylate (Sal⁻), based on the use of the salicylal-imino acid Schiff base dibenyl complex of Sn(IV) [Sn(IV)-SIADBen] as ionophore is described. The influence of lipophilic charged additives on the performance of the electrode was studied. The results suggested that Sn(IV)-SIADBen according to a positively-charged carrier mechanism. The influence of several other variables was investigated in order to optimize the potentiometric response and selectivity of the electrode. The electrode based on Sn(IV)-SIADBen, with 30.44 wt% PVC, 64.55 wt% plasticizer [dioctyl phthalate (DOP)], 3.81 wt% ionophore, and 1.2 wt% anionic additive exhibited a linear response for the Sal⁻ ion over the concentration range 1.0×10⁻¹ to 2.5×10⁻⁶ mol l⁻¹, and displayed an anti-Hofmeister selectivity sequence as follows: salicylate ≫ perchlorate > thiocyanate > benzoate > iodide > nitrate > chloride > nitrite ≈ acetate > citrate > sulfate. UV-Visible absorption spectra were used to examine the specific interaction of salicylate with the ionophore. The electrode was applied to clinical medical analysis, and the results obtained were consistent with those obtained by conventional methods.

Keywords: Salicylal-imino acid Schiff base complex of Sn(IV); Charged carrier mechanism; PVC membrane; ISE; Salicylate

Evaluation of a generalized regression artificial neural network for extending cadmium’s working calibration range in graphite furnace atomic absorption spectrometry by Edwin A. Hernández-Caraballo; Francklin Rivas; Rita M. Ávila de Hernández (pp. 788-794).

A generalized regression artificial neural network (GRANN) was developed and evaluated for modeling cadmium’s nonlinear calibration curve in order to extend its upper concentration limit from 4.0 μg L⁻¹ up to 22.0 μg L⁻¹. This type of neural network presents important advantages over the more popular backpropagation counterpart which are worth exploiting in analytical applications, namely, (1) a smaller number of variables have to be optimized, with the subsequent reduction in “development hassle”; and, (2) shorter development times, thanks to the fact that the adjustment of the weights (the artificial synapses) is a non-iterative, one-pass process. A backpropagation artificial neural network (BPANN), a second-order polynomial, and some less frequently employed polynomial and exponential functions (e.g., Gaussian, Lorentzian, and Boltzmann), were also evaluated for comparison purposes. The quality of the fit of the various models, assessed by calculating the root mean square of the percentage deviations, was as follows: GRANN > Boltzmann > second-order polynomial > BPANN > Gauss > Lorentz. The accuracy and precision of the models were further estimated through the determination of cadmium in the certified reference material “Trace Metals in Drinking Water” (High Purity Standards, Lot No. 490915), which has a cadmium certified concentration (12.00±0.06 μg L⁻¹) that lies in the nonlinear regime of the calibration curve. Only the models generated by the GRANN and BPANN accurately predicted the concentrations of a series of solutions, prepared by serial dilution of the CRM, with cadmium concentrations below and above the maximum linear calibration limit (4.0 μg L⁻¹). Extension of the working range by using the proposed methodology represents an attractive alternative from the analytical point of view, since it results in less specimen manipulation and consequently reduced contamination risks without compromising either the accuracy or the precision of the analyses. The implementation of artificial neural networks also helps to reduce the trial-and-error task of looking for the right mathematical model from among the many possibilities currently available in the various scientific and statistic software packages.

Keywords: Cadmium; Graphite furnace atomic absorption spectrometry (GFAAS); Calibration curve; Modeling; Artificial neural networks

A new hybrid strategy for constructing a robust calibration model for near-infrared spectral analysis by Da Chen; Bin Hu; Xueguang Shao; Qingde Su (pp. 795-805).

A new hybrid algorithm is proposed for construction of a high-quality calibration model for near-infrared (NIR) spectra that is robust against both spectral interference (including background and noise) and multiple outliers. The algorithm is a combination of continuous wavelet transform (CWT) and a modified iterative reweighted PLS (mIRPLS) procedure. In the proposed algorithm the spectral interference is filtered by CWT at the first stage then mIRPLS is proposed to detect the multiple outliers in the CWT domain. Compared with the original IRPLS method, mIRPLS does not need to adjust variable parameters to achieve optimum calibration results, which makes it very convenient to perform in practice. The final PLS model is constructed robustly because both the spectral interference and multiple outliers are eliminated. In order to validate the effectiveness and universality of the algorithm, it was applied to two different sets of NIR spectra. The results indicate that the proposed strategy can greatly enhance the robustness and predictive ability of NIR spectral analysis.

Keywords: Multiple outliers; Spectral interference; Modified iterative reweighted PLS; Continuous wavelet transform; Near-infrared spectroscopy

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Analytical and Bioanalytical Chemistry (v.381, #3)

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Analytical and Bioanalytical Chemistry (v.381, #3)