Showing papers in "Analyst in 1998"

Use of colloidal gold surface plasmon resonance peak shift to infer affinity constants from the interactions between protein antigens and antibodies specific for single or multiple epitopes

Abstract: The surface plasmon resonance (SPR) wavelength of colloidal gold particles coated with a monoclonal antibody is red-shifted when the antibody interacts with its specific ligand. This shift results from the change in the refractive index of the particles as induced by ligand binding. This property is used to monitor in real-time the association and dissociation kinetics of the interaction in solution. The monitoring is perfomed in a clinical chemistry automated analyzer during a few minutes of incubation at 37 °C. Data treatment allows calculation of the affinity constant of the interaction. The SPR wavelength shift does not necessarily require agglutination or aggregation of the particles to occur since particles coated with one monoclonal antibody specific for a single epitope on the ligand can be used in the procedure. The affinity constants measured by this procedure correlate with those calculated from Scatchard plots or BIAcore data.

Phenolic compounds in olives

Abstract: Introduction Structure of plant phenolics or more hydroxy substituents Role of phenolics in olives Properties and function Phenolics as antioxidants Phenolics and fruit quality Factors affecting the phenolic profile of olives Varietal influences Other factors Olive development and maturation Processing and storage Oil production Table olives Analysis Sample preparation Quantification Chromatographic methods Liquid chromatography Detection

Characterisation of radioactive particles in the environment

Abstract: When radioactive particles are released into the environment, information on the size distribution pattern, radionuclide and matrix composition, morphology and structure is essential for assessing weathering and the subsequent mobilisation and biological uptake of associated radionuclides. The particle characteristics will depend on the source in question in addition to the release scenario, dispersion processes and deposition conditions. Following high temperature accident scenarios associated with nuclear installations (e.g., Chernobyl accident) a range of different uranium fuel particles and condensed particles were observed, varying in composition, morphology and structure (e.g., crystalline and amorphous phases). Following low temperature releases (e.g., prefire Winscale releases), flake-like uranium fuel particles significantly different from those collected at Chernobyl were identified. Furthermore, a major fraction of radionuclides in effluents from reactors and reprocessing plant during normal operations are associated with particles and colloids. Hence the presence of radioactive particles or colloids in releases from nuclear sources occurs more frequently than usually expected. After deposition, weathering of particles occurs and associated radionuclides are mobilised with time. Hence the transfer of mobilised radionuclides within the ecosystem will be delayed until weathering takes place, and the assessment of short term consequences of releases may be overestimated if particles are present. The weathering rate will depend on the particle composition (e.g., UO2 fuel), structural changes occurring during the event (e.g., transformation from UO2 to U3O8) and chemical conditions after deposition (e.g., pH, redox). Unless the impact of particle weathering is taken into account, assessment of mobilisation, transfer and long-term consequences of radionuclide releases may be underestimated. In order to improve the predicting power of transport models, ecosystem transfer models and dose assessment models, experimental information is required with respect to source term radionuclide speciation and in particular the association of radionuclides with particles and colloids, influencing mobility and biological uptake. This work was therefore focused on analytical techniques applicable to the fractionation, identification and characterisation of radioactive particles and colloids (e.g., hollow fibre fractionation, electron microscopic techniques and reactivity studies) released from a source and deposited in the environment. Results from research carried out during several years at the authors’ laboratory are presented to illustrate the usefulness of the techniques.

Near-infrared spectroscopy in the pharmaceutical industry.

Abstract: Introduction Background and literature sources Specialized journals Internet addresses Previous reviews Fundamentals of the technique Principles of NIR spectroscopy NIR diffuse reflectance spectroscopy Operational procedures in the NIR Mathematical processing of signals Qualitative analysis Identification and qualification of raw materials and pharmaceutical preparations Determination of homogeneity Polymorphism and optical isomers Quantitative analysis Sample selection Multivariate calibration methods Determination of physical parameters Determination of moisture content Determination of active compounds and excipients Calibration transfer Miscellaneous applications Conclusions References

Magnetic molecularly imprinted polymer beads for drug radioligand binding assay

Abstract: Molecularly imprinted polymer–magnetic iron oxide composite materials which exhibit recognition properties and can be withdrawn from solution by application of a magnetic field were prepared for the first time. Magnetic iron oxide was incorporated using a suspension polymerisation methodology with a perfluorocarbon liquid as the dispersing phase for the preparation of methacrylic acid-1,1,1-trimethylolpropane trimethacrylate copolymer beads molecularly imprinted with the β-blocker (S)-propranolol. The resulting superparamagnetic imprinted polymer beads were capable of binding [3H]-(S)-propranolol more strongly than a non-imprinted, otherwise identical, polymer. In a competitive radioligand binding assay using a magnet to separate polymer from solution, (R)-propranolol and (R,S)-metoprolol exhibited cross-reactivities of 19 and 0.7%, respectively, compared with (S)-propranolol.

3,3′,5,5′-Tetramethylbenzidine as electrochemical substrate for horseradish peroxidase based enzyme immunoassays. A comparative study

Abstract: The use of 3,3′,5,5′-tetramethylbenzidine (TMB) as an electrochemical substrate for horseradish peroxidase (HRP) was investigated. HRP activity has been detected using flow injection analysis at a glassy carbon working electrode polarised at +100 mV versus Ag/AgCl in 0.1 mol l–1 citrate–phosphate buffer (pH 5.0). The optimum concentrations were 2 × 10–4 mol l–1 TMB and 10–3 mol l–1 H2O2. The detection limit obtained after 15 min of incubation was 8.5 × 10–14 mol l–1 HRP with the amperometric method. This limit was lower than that obtained using hydroquinone as HRP substrate and comparable to that with the p-aminophenyl phosphate–alkaline phosphatase system. Better performance was achieved with amperometric than spectrophotometric detection using TMB in a competitive ELISA for rabbit immunoglobulin G as a model analyte.

Optimization of confocal epifluorescence microscopy for microchip-based miniaturized total analysis systems

Abstract: A confocal epifluorescence detection scheme, optimized to give sub-picomolar detection within planar glass substrates etched to a 30 µm depth, is described. A ×40, 0.6 numerical aperture (N.A.) lens with a 3.7 mm working distance was used to create a focused laser spot about 12 µm in diameter, by under-filling the lens aperture to give an effective, measured N.A. of 0.22 for the laser beam. The sectioning power (optical axis field of view) of various pinholes and the corresponding detector probe volumes (overlap of the excitation and observation volumes) were: (pinhole diameter, sectioning power, probe volume): 100 µm, 18 µm, 0.1 pl; 200 µm, 20 µm, 0.4 pl; 400 µm, 26 µm, 1.7 pl; and 600 µm, 36 µm, 2.4 pl. A log–log plot of fluorescence intensity versus fluorescein concentration, measured in continuous-flow mode using the optimum 400 µm pinhole, showed a correlation coefficient of 0.996 and a slope of 0.85. In this mode, 300 fM fluorescein gave a signal of 34.6 ± 8.1 mV over background with an S/N of 6.1, representing the lowest measured fluorescein dye concentration reported on-chip. Capillary zone electrophoresis of 1 pM fluorescein resulted in a mean S/N of 5.8. The injection plug, estimated to be about 5470 molecules, corresponds to 570 detected molecules on average. The design and use of quick-fit, flangeless fittings for interfacing tubing, fused-silica capillaries or pressurized systems to microfluidic channels etched in planar glass chips is briefly presented.

Detection of residues of tetracycline antibiotics in pork and chicken meat: Correlation between results of screening and confirmatory tests.

Abstract: Residues of the tetracycline group of antibiotics were quantified in pork and chicken muscle tissue that had previously been screened with a microbiological inhibition test and an immunological method. Pieces of frozen pork and chicken meat were screened on a pH 6 culture medium seeded with Bacillus subtilis. An aqueous extract of the inhibitor-positive samples was then screened with a group-specific commercial ELISA kit, able to detect levels of oxytetracycline, chlortetracycline, tetracycline and doxycycline corresponding with the European MRL or lower. The cut-off value of the ELISA was set at a B/B0 value of 75%. Finally, confirmation and quantification were performed using a validated HPLC method with fluorescence detection. The fluorescence was induced by complexation of the tetracyclines with the zirconium cation which is added post-column to the HPLC eluate. This fluorescence makes it possible to quantitate residues below one-half of the MRL. To gain additional qualitative information some samples were also analysed with LC-MS-MS.ELISA analysis demonstrated the presence of residues of tetracyclines in 12 out of 19 inhibitor-positive pork samples and in 19 out of 21 inhibitor-positive chicken samples. Doxycycline was detected with HPLC in 10 of these 12 pork samples and in 18 out of 19 chicken samples. The two other ELISA positive pork samples contained oxytetracycline, while no tetracyclines were found in one ELISA positive chicken meat sample. The correlation between the ELISA B/B0 values and the actual levels determined with the HPLC method was poor, whereas a better correlation was observed between the inhibition zones and the doxycycline levels. Our results indicate that an inhibition test with a medium at pH 6 and B. subtilis as test organism is well suited to screen pork and chicken muscle tissue for residues of tetracycline antibiotics. Since many positive samples contained doxycycline levels below the MRL, a confirmatory method is necessary to quantify the residues.

Speciation of metals in sewage sludge for agricultural uses

Abstract: A study carried out on sewage sludge samples collected at an urban waste-water processing plant located in Zaragoza (Spain) is reported. The concentrations of metals (Cd, Co, Cr, Cu, Ca, K, Fe, Mg, Mn, Ni, Na, Pb and Zn) and agronomic parameters were determined. The speciation of metals based on the sequential extraction scheme proposed by Tessier et al. is reported. Principal component analysis was applied to the results obtained and the correlation factors are discussed. The concentration of heavy metals is lower than that established by European legislation. Heavy metals are mainly associated with the mineral fraction and consequently they show a low availability index.

Bioavailability and speciation of arsenic in carrots grown in contaminated soil

Abstract: Carrots were grown in seven experimental plots (A–G) containing mixtures of arsenic-contaminated and uncontaminated soil at concentrations ranging from 6.5 to 917 µg g–1 (dry mass). The carrots harvested from plots A–D (6.5–338 µg g–1 arsenic in the soil mixtures) showed a gradually increasing depression of growth with increasing level of contamination. At the experimental plots E–G with soil arsenic concentrations above 400 µg g–1 no carrots developed. Whether this effect was caused by arsenic or the concomitant copper content which ranged from 11 to 810 µg g–1 in the soil mixtures is unknown. The arsenic species extracted from the soils and carrots were separated and detected using anion-exchange HPLC coupled with ICP-MS. In the less contaminated soils from plots A and B arsenite (AsIII) was more abundant than arsenate (AsV) in the soil using 1 mmole l–1 calcium nitrate as extractant. In the soils from plots C and D however, AsV dominated over AsIII whereas in the corresponding carrots AsV and AsIII were found at similar concentrations. Methylated arsenic species were sought after but not detected in any of the samples. The soil-to-carrot uptake rate (bioavailability) of arsenic was 0.47 ± 0.06% (average ± one standard deviation) of the arsenic content in the soils from plots A–D. In contrast to arsenic, the increasing copper content in the soils from plot A through D was not available to the carrots as the concentration of this element did not increase with increasing soil copper content. The ingestion of the potentially toxic inorganic arsenic via consumption of carrots grown in soil contaminated at 30 µg g–1 in arsenic (plot B) was conservatively estimated at 37 µg week–1. This was equivalent to only 4% of the provisional tolerable weekly intake (PTWI) for inorganic arsenic as suggested by the WHO and was therefore toxicologically safe. Consumption of carrots grown in more intensely arsenic-contaminated soils, however, would lead to a higher intake of inorganic arsenic and is therefore not recommended.

Analysis of carbonaceous aerosols: interlaboratory comparison

Abstract: Carbonaceous aerosols are present in many workplace and environmental settings. Some of these aerosols are known or suspect human carcinogens and have been linked to other adverse health effects. Exposure to diesel exhaust is of particular concern because it has been classified as a probable human carcinogen and use of diesel-powered equipment is widespread in industry. Because previously used methods for monitoring exposures to particulate diesel exhaust lack adequate sensitivity and selectivity, a new method was needed. A carbon analysis technique called the ‘thermal–optical method’ was evaluated for this purpose. In thermal–optical analysis, carbon in a filter sample is speciated as organic and elemental (OC and EC, respectively). When the thermal–optical method was initially evaluated, only one instrument was available, so interlaboratory variability could not be examined. More recently, additional instruments were constructed and an interlaboratory comparison was completed. Eleven laboratories participated in the study, including four in Europe that employ an alternative thermal technique based on coulometric detection of CO2. Good agreement (RSDs ≤ 15%) between the total carbon results reported by all laboratories was obtained. Reasonable within-method agreement was seen for EC results, but the EC content found by the two methods differed significantly. Disagreement between the OC–EC results found by the two methods was expected because organic and elemental carbon are operationally defined. With all filter samples, results obtained with the coulometric method were positively biased relative to thermal–optical results. In addition, the alternative method gave a positive bias in the analysis of two OC standard solutions. About 52% and 70% of the carbon found in two aqueous solutions containing OC only (sucrose and EDTA, respectively) was quantified as elemental, while EC contents of about 1% and 0.1% (respectively) were found by the thermal–optical method. The positive bias in the analysis of the OC standards is attributed largely to inadequate removal of OC during the first part of the analysis; lack of correction for pyrolytically formed carbon (char) also is a factor. Results obtained with a different thermal program having a higher maximum temperature were in better agreement with the thermal–optical method.

Rheumatoid arthritis and metal compounds—perspectives on the role of oxygen radical detoxification†

Abstract: Rheumatoid arthritis (RA) is characterised by migration of activated phagocytes and other leukocytes into synovial and periarticular tissue. Activated oxygen species and other mediating substances from triggered phagocytes appear to exacerbate and perpetuate the rheumatoid condition. Iron excesses are capable of aggravating the arthritic inflammation, probably through their pro-oxidant potentials. In contrast, therapeutically given gold salts, through a lysosomal loading of the metal, inhibit the triggered cells, thereby reducing the toxic oxygen production. Pharmacological doses of zinc also may immobilise macrophages. Furthermore, the copper-zinc-containing enzyme SOD (superoxide dismutase) can act as a scavenger of toxic oxygen in the tissues. Therapeutic remission of RA has been obtained following intraarticular administration of SOD. Intramuscular administration of copper complexes has induced remission in about 60% of RA patients in open studies. Another drug, penicillamine, that protects cellular membranes against toxic oxygen in vitro, is presumed to act as an antirheumatic via the SOD mimetic activity of its copper complex. Thiomalate and other thiols may possess similar activities. Selenium compounds also may act as oxygen radical scavengers. A significant alleviation of articular pain and morning stiffness was obtained following selenium and vitamin E supplementation in a double-blind study on RA patients. The observations reviewed here indicate that metal compounds and other antioxidants can reduce the rheumatic inflammation by reducing the cellular production and/or concentration of toxic oxygen species.

Application of 2-mercaptobenzothiazole-modified silica gel to on-line preconcentration and separation of silver for its atomic absorption spectrometric determination

Abstract: 2-Mercaptobenzothiazole-modified silica gel was used for the flow injection on-line preconcentration–separation and determination of silver by flame atomic absorption spectrometry. Two types of manifold, with one or two columns, were adopted. The results showed that Ag+ was selectively adsorbed from 0.05 to 6 M HNO3 solution and was readily desorbed by thiourea solution. The ions co-existing with Ag+ exhibit virtually no interference in the determination with the exception of Cl–. An Ag+ concentration as low as 1 ppb could be determined reliably if a long preconcentration time was used. The sample throughput was 60 h–1 using the two-column manifold with a preconcentration time of 60 s. Silver in a geological sample, a copper metal sample and a lead nitrate sample was determined satisfactorily.

In vitro mineral availability from digested tea: a rich dietary source of manganese

Abstract: Tea is potentially a rich source of some dietary metals and approximately 70 l are drunk per capita per year in the UK. In particular, tea may be an important source of Mn, since leaf tea contains 350–900 µg g–1 of this essential element. However, the leaching and bioavailability of Mn from tea have been little studied, so a recently developed in vitro assay was applied to compare the bioavailability of Mn from tea infusions with that of other major and trace essential elements. Analysis of tea infusions before digestion showed that 1.0 l contained 115% of the average daily dietary intake of Mn but M2+ > M3+, which is probably the inverse of the order of their strengths of binding to tea polyphenols. However, Mn was the only element found in significant dietary amounts in tea, and under simulated intestinal conditions was still 40% bioavailable.

Selenium speciation in human body fluids

Abstract: Selenium consumed by humans in foods and in supplements exists in a number of different organic and inorganic forms including selenomethionine, selenocysteine, selenate and selenite. Animal and human studies have established that the bioavailability of the selenium depends upon the chemical form, which also influences the distribution of selenium in the body. These studies have included urinary excretion of selenium following ingestion of different forms of selenium, and the response of tissue selenium concentrations and activities of functional selenoproteins to these selenium compounds. Selenomethionine is retained in tissue proteins to a greater extent than selenocysteine and the inorganic forms, but the selenium is not necessarily immediately available for functional selenoproteins. A number of other factors besides chemical form may also influence the bioavailability and distribution of selenium, including other dietary components, selenium status, physiological status and species. Knowledge of these factors and of speciation of selenium in foods, tissues and functional selenoproteins is important for the accurate assessment of selenium status. Speciation of selenium also has implications with respect to the determination of selenium requirements and to the investigation of relationships between selenium status and health and disease.

Capillary electrochromatography. Tutorial Review

Abstract: Capillary electrochromatography (CEC) has seen a resurgence of interest during the 1990s, despite having origins in the 1970s. The technique combines the desirable features of both high-performance liquid chromatography (HPLC) and capillary electrophoresis (CE): the separation process is based on differential interactions between the stationary and mobile phases, whilst the electroosmotic flow transports the mobile phase through the capillary. Thus, it has demonstrated advantages over both HPLC and CE, which are yet to be fully exploited over a wide field of application; already the popularity of CEC is on the increase, as reflected in the number of scientific publications and seminars held. The aim of this tutorial review is to increase awareness and understanding of both theoretical and practical aspects of CEC. Whilst it does not provide an in-depth account of CEC, it does attempt to cover the more important, relevant work available in the open literature: only major advancements associated with CEC applications are highlighted. Material presented in the review was typically obtained by literature searches involving Analytical Abstracts, Chemical Abstracts and ‘BIDS’ (for academic use only).

Platinum concentrations in urban road dust and soil, and in blood and urine in the United Kingdom†

Abstract: Increasing Pt concentrations from vehicle catalysts have been reported from a number of countries. Analysis of Pt and Pd in soils and road dusts taken from areas of high and low traffic flows in SE England show concentrations of Pt in the range <0.30–40.1 ng g–1 and Pd in the range <2.1–57.9 ng g–1. Higher concentrations of Pt are associated with high traffic densities. Samples taken from streets of lower traffic flows were found to contain the lower concentrations of the ranges. Pilot studies of Pt concentrations in blood and urine using ICP-MS have been carried out. Platinum concentrations in whole blood were: precious metal workers, 780–2170, mean 1263 pmol l–1 (0.152–0.423, mean 0.246 µg l–1); motorway maintenance workers, 645–810, mean 744 pmol l–1 (0.126–0.158, mean 0.145 µg l–1); Imperial College staff, 590–713, mean 660 pmol l–1 (0.115–0.139, mean 0.129 µg l–1). Platinum concentrations in urine in pmol Pt per mmol creatinine were: precious metal workers, 122–682, mean 273 [0.21–1.18, mean 0.47 µg Pt (g creatinine)–1]; motorway maintenance workers, 13–78, mean 33.7 [0.022–0.135, mean 0.058 µg Pt (g creatinine)–1]; Imperial College staff, 28–130, mean 65.6 [0.048–0.224, mean 0.113 µg Pt (g creatinine)–1]. Detection limits were 0.03 µg l–1 for both blood and urine. The possible health effects of increasing Pt in the environment are discussed. Platinum provides an excellent example of the significance of speciation in metal toxicity. Platinum allergy is confined to a small group of charged compounds that contain reactive ligand systems, the most effective of which are chloride ligand systems. Metallic Pt is considered to be biologically inert and non allergenic and since the emitted Pt is probably in the metallic or oxide form, the sensitising potential is probably very low. Platinum from road dusts, however, can be solubilised, and enter waters, sediments, soils and the food chain. There is at present no evidence for any adverse health effects from Pt in the general environment, particularly allergic reactions.

Selective voltammetric method for uric acid detection using pre-anodized Nafion-coated glassy carbon electrodes

Abstract: Electrochemically pre-anodized Nafion-coated glassy carbon electrodes (NCGCEs) were used for the selective determination of uric acid (UA) by square-wave voltammetry. The major interference from ascorbic acid (AA) was overcome owing to the distinct ability of the pre-anodized NCGCE to yield its best performance at around pH 5. At pH 5, AA exists in the anionic form whereas UA is in the cationic form, since their pKa values are 4.1 and 5.4, respectively, at 25 °C. Consequently, the Nafion film repels the negatively charged AA and selective sensing of UA can be achieved. Moreover, the anodized surface has a high affinity towards UA through hydrogen bonding. Hence the combination of pre-anodization and the Nafion film modification works excellently in the determination of UA. Under optimized conditions, the detection limit for UA has been improved to 10 nM (S/N = 3). The practical analytical utility of the method is demonstrated by the measurement of UA in human urine without any preliminary treatment.

Electrochemical and microscopic characterisation of platinum-coated perfluorosulfonic acid (Nafion 117) materials

Abstract: Platinum-coated Nafion 117 structures were characterised using electrochemical measurements of platinum surface area and a number of microscopy techniques. The morphology and composition of the platinum deposits were related to their preparation conditions in terms of platinum salt concentration, electrolyte flow and the surface roughness of Nafion 117. Platinum surface areas achieved were higher than the values predicted for ideal spherical platinum particles of average diameter. This is due to a fine microstructure, which realises much smaller platinum particles than average (down to about 50 nm) allied to the geometry produced by their clustering to form nodules (about 0.1–1.5 µm diameter micro-nodules and about 3–5 µm macro-nodules). Adherent platinum deposits with high surface areas were promoted by using roughened Nafion 117 membranes and enhancing the mass transport of chloroplatinate and tetraborohydrate ions by magnetic stirring of the electrolyte. A flow cell produced much more reproducible platinum-coated Nafion 117 structures. At best, platinum surface areas of 30–50 m2 g–1 Pt were achieved at platinum penetration depths of 5–30 µm into the membrane surface.

Risk assessment in relation to neonatal metal exposure

Abstract: Rapid changes in organ development and function occur during the neonatal period. During this period the central nervous system is in a rapid growth rate and highly vulnerable to toxic effects of, e.g., lead and methylmercury. Furthermore, the kinetics of many metals is age-specific, with a higher gastrointestinal absorption, less effective renal excretion as well as a less effective blood-brain barrier in newborns compared to adults. Due to their low body weight and high food consumption per kg of body weight, the tissue levels of contaminants can reach higher levels in newborns than in adults. Generally, there is a low transfer of toxic metals through milk when maternal exposure levels are low. However, knowledge is limited about the lactational transport of metals and the potential effects of metals in the mammary gland on milk secretion and composition. There are some data from rodents on the lactational transfer and the uptake in the neonate of inorganic mercury, methylmercury, lead and cadmium. Metal levels in human breast milk and blood samples from different exposure situations can give information on the correlation between blood and milk levels. If such a relationship exists, milk levels can be used as an indicator of both maternal and neonatal exposure. Better understanding of the neonatal exposure, including kinetics in the lactating mother and in the newborn, and effects of toxic metals in different age groups is needed for the risk assessment. Interactions with nutritional factors and the great beneficial value of breast-feeding should also be considered.

Determination of benzene and associated volatile compounds in mainstream cigarette smoke

Abstract: There is continuing interest, by health professionals and individuals, in the composition of mainstream tobacco smoke. Regular official surveys of tar, nicotine and carbon monoxide yields are from time to time supplemented by special surveys of specific components. In this study, gas chromatography–mass spectrometry was used to identify and quantify benzene and certain other volatile compounds of interest in the mainstream smoke of 26 cigarette brands on the UK market and of smoke from hand rolled tobacco. Validation of the method adopted demonstrated the ability to identify and to measure reliably the yields of benzene and seven other compounds: toluene, ethylbenzene, m/p-xylene, o-xylene, styrene, isoprene and acrylonitrile. Yields of these analytes were ranked and compared with the tar yields of the brands. In general terms, brands yielding ≤3 mg of tar yielded proportionately more of the vapour phase analytes than did brands yielding >3 mg of tar per cigarette. For many of the higher tar brands the yield of vapour phase analyte was approximately proportional to the tar yield. Smoking cigarettes with an average yield of 50 µg of benzene per cigarette has been compared with the occupational maximum exposure limit (16 mg m–3) concentration and with US studies on the home environment. Smoking the majority of brands examined could contribute significantly to the population exposure of benzene and the other volatile organic compounds considered in this study.

Determination of the crystallinity of calcined and graphitic cokes by X-ray diffraction†

Abstract: Although the Scherrer equation has been the basis of the XRD method for the determination of the crystallinity of calcined coke, the most accurate interpretation of coke crystallinity involves profile analysis. In this paper, the general background related to coke crystallinity (Lc) determination is described, Alcan and ASTM standard methods are compared and line breadth as a function of crystallite size is characterized. At present, it is generally understood that the coke graphitization process occurs during calcination of coke and is related not only to the calcination temperature, but also to other parameters (composition, process conditions). As coke graphitization affects electrolytic cell performance, it should be monitored and quantified. The methods used for the determination of the degree of graphitization (DOG) and described in the literature are useful for cases involving calcination temperatures above 1800 °C. These methods are critically examined. Because known methods do not apply to the low-temperature graphitization processes (1200–1500 °C), a new approach was conceived. It is based on profile line analysis and an estimate of the graphitic contribution in coke specimen can be made. The new approach involves a commercial X-ray diffractometer and a corresponding software package and relies on profile fitting of the (002) coke peak. A calcined coke specimen or the presence of a graphitic portion in calcined coke can then be clearly recognized. During the profile fitting operation it is possible to resolve the graphitic portion from the calcined peak profile mathematically, and then to express it quantitatively. Among several profile functions that were tested, the split Pearson VII was found to give the best fit to data corresponding to calcined coke. A novel equation by which the DOG can be estimated in calcined coke is given. Selected examples of the DOG determination are described.

Kinetic approach to the chemical speciation of trace metals in soils

Abstract: The reactivity of trace metals (Cd, Pb, Zn, Cu) present in two polluted soils was studied using two extractants, EDTA and hydroxylamine. As the classical chemical speciation of trace metals in soils when using these reagents seems to be unreliable (readsorption phenomena, non-selectivity of chemical reagents, soil/solution ratio, etc.), we applied two different kinetic approaches to the results in order to determine the speciation of trace metals in the two soil samples studied. The advantages of and problems with these approaches are discussed.

Trends in electrochemical biosensors

Abstract: The development of electrochemically based biosensors is discussed in the context of what has been learned from the successful development of glucose biosensors. Some future trends are discussed.

Comparative study of the luminescent properties of europium and terbium coordinated with thenoyltrifluoroacetone or pyridine-2,6-dicarboxylic acid in aqueous solutions

Abstract: The chelates formed with europium(III) and terbium(III) coordinated with either thenoyltrifluoroacetone or pyridine-2,6-dicarboxylic acid were studied. The formation and the composition of the chelates were compared with respect to the number of donor groups of the ligand and the coordination number of the lanthanide ion. The luminescent properties of the chelates were investigated and compared in terms of the relative luminescence intensity, the linear dynamic range and the detection limit. The results are discussed with respect to the stoichiometry of the chelate, the lifetime of the emitting level and the energy gap between the donor level of the ligand and the emitting level of the ion.

Novel polypyrrole based all-solid-state potassium-selective microelectrodes

Abstract: Potassium-selective potentiometric microelectrodes with a polypyrrole solid internal contact were fabricated by the application of a potassium-selective bis-crown ether ligand based, plasticized poly(vinyl chloride) (PVC) membrane to the surface of conducting polymer modified Pt, Au or C micro disk electrodes. The selectivity and sensitivity of the new type of potentiometric potassium microelectrode were found to be comparable with those of the conventional macro ion-selective electrodes and of the micropipet type microelectrodes based on the same ionophore. The ease of preparation and robustness are the main advantages of this new electrode design, which can replace the classical micropipet type microelectrodes in many applications. The microelectrodes showed good dynamic characteristics and were used successfully in a wall-jet cell incorporated flow injection analysis system and as a measuring tip in scanning electrochemical microscopy. The polypyrrole modified substrate electrodes can be made selective for different ions just by changing the ionophore in the plasticized PVC membrane, which can extend their use to a wide range of applications.

Near-infrared mass median particle size determination of lactose monohydrate, evaluating several chemometric approaches

Abstract: The influence of particle size on near-infra red (NIR) spectra is typically considered a ‘nuisance factor’ which many scatter correction methods attempt to eliminate, e.g., multiplicative scatter correction. However, particle size is a key issue in the formulation of many pharmaceutical products and has a profound effect on the behaviour of both raw materials and drug substances during formulation. NIR has already been demonstrated as a potential alternative particle sizing technique to current accepted methodology. This investigation assessed several chemometric approaches that model this information, using lactose monohydrate as the raw material. A variety of modelling techniques were applied to both zero order and second derivative spectra namely multiple linear regression, partial least squares, principal component regression and artificial neural networks. One further data transformation evaluated was polar coordinates, although no statistical data were generated. Typically, cross-validation root mean square errors of calibration and cross-validation root mean square errors of prediction of approximately 5 µm were calculated for all of the modelling techniques. These values are comparable to those associated with the reference technique (laser diffractometry). Correlation coefficients of approximately 0.98 for all techniques were also calculated. The predictive abilities for models generated using second derivative spectra were found to be comparable to those obtained using zero order spectra.

Speciation as an analytical aid in trace element research in infant nutrition

Abstract: The aim of this work was twofold: to study the binding pattern of trace elements in formulas as compared with breast milk and the relationship between trace elements in breast milk and in maternal dietary intake. To investigate the binding form of trace elements in these nutritive fluids, methods for protein separation were combined with methods for trace element determination in the eluted fractions. HPLC and ICP-AES or ICP-MS were coupled on-line for the simultaneous speciation of elements of nutritional interest, viz., Ca, K, Mg, P, S, Co, Cu, Fe, I, Mn, Mo, Se and Zn, and also the heavy metals Cd and Pb in both human milk whey and formulas. In order to minimize interactions between the labile metal protein complexes and the column material, size-exclusion chromatography was used for protein separation. The binding pattern of trace elements in formulas is significantly different from that in breast milk and depends on its main component (cow’s milk or soy), its processing (hydrolysis) and the chemical form (inorganic) of the added compounds. For example, compared with breast-fed infants the iron supply of formula-fed infants is much higher (up to 20-fold); in addition, the binding forms of Fe are very different in the two fluids. This has to be evaluated with respect to interactions with other elements during intestinal uptake. The investigation of breast milk samples from different regions of the world showed comparable shapes for the elution profiles and for Mo and Se a dependence on the regional maternal dietary intake. Speciation studies carried out on breast milk samples as a function of the selenium content showed significant changes in the zinc-binding pattern. In particular, citrate (as a zinc-binding component) was found to decrease with increasing dietary selenium intake of the mother.