Showing papers in "Analyst in 1996"
TL;DR: In this article, the approaches for achieving oriented coupling of antibodies to increase the antigen binding capacity are reviewed and some issues such as steric hindrance caused by neighbouring antibody molecules, the distance between an antibody and the support surface and the use of antibody fragments are dealt with.
Abstract: The immobilization of antibodies on solid-phase materials has been used in many areas such as purification, diagnostic immunoassays and immunosensors. Problems associated with the loss of biological activity of the antibodies upon immobilization have been noticed in many cases. One of the main reasons for such loss is attributed to the random orientation of the asymmetric macromolecules on support surfaces. In this paper, the approaches for achieving oriented coupling of antibodies to increase the antigen binding capacity are reviewed. Some issues such as steric hindrance caused by neighbouring antibody molecules, the distance between an antibody and the support surface and the use of antibody fragments are dealt with. Some applications of the oriented immobilized antibodies in immunoassays and immunosensors are examined.
351 citations
TL;DR: Results of investigation of a thermal-optical technique for the analysis of the carbonaceous fraction of particulate diesel exhaust are discussed and elemental carbon is the superior marker of diesel particulate matter.
Abstract: Diesel exhaust has been classified a probable human carcinogen, and the National Institute for Occupational Safety and Health (NIOSH) has recommended that employers reduce workers' exposures. Because diesel exhaust is a chemically complex mixture containing thousands of compounds, some measure of exposure must be selected. Previously used methods involving gravimetry or analysis of the soluble organic fraction of diesel soot lack adequate sensitivity and selectivity for low-level determination of particulate diesel exhaust; a new analytical approach was therefore needed. In this paper, results of investigation of a thermal–optical technique for the analysis of the carbonaceous fraction of particulate diesel exhaust are discussed. With this technique, speciation of organic and elemental carbon is accomplished through temperature and atmosphere control and by an optical feature that corrects for pyrolytically generated carbon, or ‘char,’ which is formed during the analysis of some materials. The thermal–optical method was selected because the instrument has desirable design features not present in other carbon analysers. Although various carbon types are determined by the method, elemental carbon is the superior marker of diesel particulate matter because elemental carbon constitutes a large fraction of the particulate mass, it can be quantified at low levels and its only significant source in most workplaces is the diesel engine. Exposure-related issues and sampling methods for particulate diesel exhaust also are discussed.
244 citations
TL;DR: In this article, a new method for the simultaneous determination of 60 pesticides by solid-phase microextraction and gas chromatography-mass spectrometry is presented, where both polyacrylate-and polydimethylsiloxane-coated fibres are used to extract the analytes directly from the samples over the concentration range 0.1-100 µg l-1.
Abstract: A new method for the simultaneous determination of 60 pesticides by solid-phase microextraction and gas chromatography–mass spectrometry is presented. The analyte mixture contains representatives from each of the organonitrogen, organochlorine and organophosphorus classes. Both polyacrylate-and polydimethylsiloxane-coated fibres are used to extract the analytes directly from the samples over the concentration range 0.1–100 µg l–1. The performances of the two types of coating were compared. The limits of detection with both coatings were determined to be at the ng l–1 to sub-ng l–1 levels, depending on the selectivity of the coating for an analyte. The method was applied to the analysis of samples obtained from the Russian and Canadian Arctic. A contaminated groundwater sample and a contaminated soil sample, both containing metolachlor, were analysed by the proposed method and the results were found to be comparable to those obtained by a liquid–liquid extraction method. Orange juice was spiked with the 60 pesticides and their recoveries were determined.
185 citations
TL;DR: A correction method for the mass discrimination effect was developed for isotopic analyses using multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS).
Abstract: A correction method for the mass discrimination effect was developed for isotopic analyses using multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS) For Pb isotopic analysis using MC-ICP-MS, the correction factor for the mass discrimination effect on Pb is based on the addition of TI to the sample solution and measurement of TI isotopic ratios; the correction factor obtained using Tl is directly applied to the Pb isotopes (conventional external correction) However, the series of measurements of discrimination factors for several elements, including Rb, Sr, Ru, Nd, Hf, Re, Os, Tl and Pb (mass range 80–210 u), clearly reveal that the mass discrimination factors observed using MC-ICP-MS were a linear function of mass, suggesting that the correction factors observed using Tl isotopes were not exactly identical with those for Pb isotopes Therefore, the correction factors obtained with Tl isotopes should be corrected for mass, and then applied to the Pb isotopes The resultant Pb isotopic ratios for NIST Standard Reference Materials show excellent agreement (within 003% for 206Pb/204Pb and 20 ppm for 207Pb/206Pb) with the data obtained by the thermal ionization mass spectrometry The correction method presented clearly demonstrates the wide versatility of the external correction technique for the precise isotopic analysis using MC-ICP-MS The possible cause of the ‘exceptionally large’ mass discrimination effect observed for Ru and Os is discussed
183 citations
TL;DR: In this paper, a dissolved oxygen sensor based on the quenching of fluorescence from a ruthenium dye complex entrapped in a porous sol-gel film is reported.
Abstract: A dissolved oxygen sensor based on the quenching of fluorescence from a ruthenium dye complex entrapped in a porous sol–gel film is reported. Sol–gel-derived silica films were fabricated by dip-coating on to planar and optical fibre substrates. The films were pre-doped with the oxygen-sensitive ruthenium complex [RII–tris(4,7-diphenyl-1,10-phenanthroline)], the fluorescence of which is quenched in the presence of oxygen. The structure and behaviour of sol–gel films are dependent on the fabrication parameters. In particular, enhancement of the surface hydrophobicity increases the quenching response in water. This is achieved by using suitable proportions of modified precursors of silica of the form R(OEt)3Si, where R is an alkyl group, in the standard fabrication procedure. It is shown that by increasing the ratio of modified precursor, the quenching response in the aqueous phase increases. A very low limit of detection, 6 ppb, was determined for the modified films. Using a high-brightness blue LED, combined with a miniature photodiode detection system, these results indicate the potential for a low-cost, high-performance, portable dissolved oxygen sensor for use in many varied situations from aeration control to on-line river pollution monitoring.
179 citations
TL;DR: In this paper, the relationship between the structural attributes of various amine compounds and their observed electrogenerated chemiluminescence (ECL) activity with the tris(2,2-bipyridine)ruthenium(II) reaction was examined, with a view to the determination of these compounds.
Abstract: The relationship between the structural attributes of various amine compounds and their observed electrogenerated chemiluminescence (ECL) activity with the tris(2,2-bipyridine)ruthenium(II) ECL reaction was examined, with a view to the determination of these compounds. This was carried out by first examining the reaction mechanism and then predicting the ECL activity of certain classes of compounds by considering the stability of intermediates, and drawing general conclusions by comparing the observations obtained by the authors and other workers. The molecular geometry and alternative anodic reactivity and their effect on ECL activity are discussed and results for the ECL activity of a range of local anaesthetics are presented.
177 citations
TL;DR: The construction and application of conducting polymers for use as biosensors are the particular emphasis of this paper and biocompatibility is briefly discussed.
Abstract: This review covers the evolution of conducting polymers and their use in the bioanalytical sciences. It is the controlled dynamic behaviour of these unique materials that enables such diverse and high-level performance to be achieved. The construction and application of conducting polymers for use as biosensors are the particular emphasis of this paper. Biocompatibility is briefly discussed.
164 citations
TL;DR: In this article, a rapid electrochemical procedure for in situ activation of screen-printed electrodes was established, and short pre-anodization periods were shown to increase the electrochemical activity for a wide range of irreversible and quasi-reversible redox processes.
Abstract: Screen-printed electrodes, fabricated by thick-film technology, represent an attractive avenue for routine electrochemical sensing. However, the composite character of strips fabricated from commercial carbon strips results in slow rates of heterogeneous electron transfer. The aim of this study was to establish a rapid electrochemical procedure for in situ activation of screen-printed electrodes. Short pre-anodization periods were shown to increase the electrochemical activity for a wide range of irreversible and quasi-reversible redox processes. Activation parameters influencing the enhanced reversibility at strips fabricated from two common carbon inks were explored. The effect of the ink-curing temperature on the redox activity was also examined. Cyclic and differential-pulse voltammetry, X-ray photoelectron spectroscopy and scanning electron microscopy were used for monitoring changes in the electrochemical reversibility, surface area and morphology and the introduction of oxygen surface functionalities. The sensing utility of activated carbon strip electrodes is demonstrated for several analytes, and future prospects are discussed. The simple, yet effective, electrochemical pretreatment is compatible with on-site application of disposable electrodes.
162 citations
TL;DR: A series of fluorescent sensors for transition metal ions were synthesized by linking a light-emitting subunit, anthracene, to a polyaza chelating subunit (either a dioxotetraamine or a tetraamine) as discussed by the authors.
Abstract: A series of fluorescent sensors for transition metal ions were synthesized by linking a light-emitting subunit, anthracene, to a polyaza chelating subunit, either a dioxotetraamine or a tetraamine. Sensing of the divalent cations CuII, NiII and ZnII was investigated through spectrofluorimetric titrations in acetonitrile–N water (4:1) solutions. The selective recognition of CuII and NiII among other transition and non-transition metal ions is signalled through full quenching of fluorescence; discrimination between the two ions can be achieved by performing titrations at controlled pH. The system containing the tetraamine fragment, whose interaction with CuII and NiII induces fluorescence quenching, is also sensitive to ZnII, but in this case the recognition is signalled through a fluorescence enhancement.
144 citations
TL;DR: A method has been developed which separates the three major selenium-containing proteins found in human blood serum and plasma: selenoprotein-P, glutathione peroxidase and albumin, and the Se content determined directly by ETAAS was determined.
Abstract: A method has been developed which separates the three major selenium-containing proteins found in human blood serum and plasma: selenoprotein-P, glutathione peroxidase and albumin. They were separated from plasma or serum by affinity chromatography and the Se content determined directly by ETAAS. Selenoprotein-P is retained on a heparin-Sepharose column, and subsequently eluted with an excess of heparin, while glutathione peroxidase is separated by a blue-Sepharose column. The amount of Se associated with albumin was assumed to be the Se remaining in the rest of the sample. The detection limit of the ETAAS method, when applied to the separated fractions, was 0.8 µg l–1(2 ng absolute) and the accuracy of the determination was confirmed by comparison with spectrofluorimetry. The distribution of Se in the serum or plasma of 21 healthy people was determined, showing that 53 ± 6% of the total present is associated with selenoprotein-P, 39 ± 6% as glutathione peroxidase and 9 ± 4% as albumin.
136 citations
TL;DR: The results obtained by the proposed method and the certified values are in good agreement and represent the practical detection limit of this method.
Abstract: A method for determining iodine, bromine, chlorine and fluorine in geological and biological materials is described. In a quartz tube, solid material was heated to 1100 °C under a wet oxygen flow (pyrohydrolysis). By this process the halogens (I, Br, Cl, F) were separated from the matrix and then collected in a receiver solution. The chemical yield of iodine was determined by a radioactive tracer. ICP-MS and ion chromatographic measurements were used for the determination of the halogens. The method was optimized by investigating different experimental conditions. All four halogens can be trapped in the receiver solution from one combustion procedure. Precision and accuracy were evaluated by the analysis of environmental standard reference materials (rock, soil, milk, leaves, marine tissue). The concentrations in the materials analysed were in the ranges 0.006–50 mg kg–1 for I, 0.06–1300 mg kg–1 for Br, 50–1100 mg kg–1 for F and 400–1100 mg kg–1 for Cl. The lower values represent the practical detection limit of this method. The results obtained by the proposed method and the certified values are in good agreement.
TL;DR: In this paper, the adsorption of heavy metal cations on two TiO2(anatase) samples was investigated, one was synthesized by hydrolysis of TiCl4, whereas the second was a commercial product.
Abstract: The adsorption of heavy metal cations on two TiO2(anatase) samples was investigated. The first sample (T1) was synthesized by hydrolysis of TiCl4, whereas the second (T2) was a commercial product. The adsorption kinetics, pH curves, adsorption isotherms and adsorption capacities were studied. Sample T1 possesses a significant capacity towards sorption of heavy metal cations (approximately 5000 µg g–1), which is much higher than the adsorption capacity of the commercial sample T2 and, in most instances, higher than the capacity of silica. Quantitative and fast sorption of various heavy metal ions in trace concentrations on T1 occurs, but in different pH ranges for each element. At pH 8 quantitative sorption was detected for Bi, Cd, Co, Cr, Cu, Fe, Ge, In, Mn, Ni, Pb, Sb, Sn, Te, Tl, V and Zn. All of the elements can be eluted with HNO3 and EDTA and this procedure does not adversely affect the titania for subsequent sorptions. On the basis of the results obtained, optimum conditions for the joint and quantitative solid-phase extraction of the most common heavy metal ions are proposed. A column system for preconcentration was developed. The conditions for the quantitative and reproducible elution and of subsequent AAS were established. A method for the determination of trace elements in different waters is proposed. It is characterized by high precision, reproducibility and concentration factor.
TL;DR: In this article, a strain of Fusarium sporotrichioides Sherbakoff was cultured on straw, wheat and oat grains at a relative humidity of air (RH) of 84-100% for 17 days.
Abstract: A toxigenic strain of Fusarium sporotrichioides Sherbakoff was cultivated on straw, wheat and oat grains at a relative humidity of air (RH) of 84–100% for 17 days. Likewise, toxigenic and non-toxigenic strains of Penicillium verrucosum Dierckx were cultured on oat grain, aspen wood and wallpaper at RH 78–98% for 26 days. During the incubation, air samples were collected from the incubation chambers into Tenax TA adsorbent tubes every second day, and 12 microbial volatile organic compounds (MVOC) were identified from the air samples by thermal desorption–gas chromatography. The main MVOC included oct-1-en-3-ol, 3-methylbutan-2-ol, octan-1-ol, octan-3-ol, octan-3-one, hexan-2-one, heptan-2-one, α-pinene, and limonene. Especially ketones were formed in the grain cultures, possibly because of the high lipid content of grain. A relationship between the synthesis of mycotoxins and the relative proportion of different MVOC groups was detected, probably resulting from similar metabolic pathways. The production of volatile terpenes seemed to be linked to the formation of trichothecenes in the F. sporotrichioides cultures, and the P. verrucosum strain that is capable of synthesizing ochratoxin showed an accelerated production of volatile ketones compared with the ketone production of the non-toxigenic strain.
TL;DR: A historical account in the form of a retroanalysis of the success story behind the rational design of the first enzymically triggerable, CIEEL-active AMPPD chemiluminescent probe is given.
Abstract: Chemiluminescent dioxetanes, which are enzymically triggerable, have proved to be a valuable tool in diagnostic clinical applications. In this context, the phenomenon of firefly bioluminescence (the most efficient light-producing system so far) has served as an excellent example to develop new chemiluminescent probes for bioanalysis, in particular chemiluminescence immunoassays. From the recognition of the molecular details of the firefly bioluminescence, a chemical equivalent has been conceived which possesses the essential features for efficient generation of light, i.e., thermal persistence through spiroadamantyl substitution, spontaneous chemically initiated electron exchange luminescence (CIEEL)-active decomposition after enzymic triggering, efficient light emission as a lasting glow and convenient synthesis by photooxygenation. This has led to a rationally designed dioxetane, namely the 3-(2′-spiroadamantyl)-4-methoxy-4-(3″-phosphoryloxy)-phenyl-1,2-dioxetane (AMPPD) derivative, which serves as a substrate for alkaline phosphatase and, in terms of sensitivity, has surpassed the hazardous radioactive immunoassay probes. This paper gives a historical account in the form of a retroanalysis of the success story behind the rational design of the first enzymically triggerable, CIEEL-active AMPPD chemiluminescent probe.
TL;DR: In this paper, the use of biocomposite materials in the construction of amperometric biosensors is discussed. But the authors do not discuss the application of such composites in the biomedical field.
Abstract: This paper reviews the use of biocomposite materials in the construction of amperometric biosensors. These rigid composites are formed by dispersing graphite particles in assorted polymers (especially epoxy resins). These composites are bulk-modified biologically (adding enzymes and cofactors) and chemically (blending mediators and catalysts).
TL;DR: In order to widen the applicability of MVOC analysis, it is necessary to increase this analysis by including more volatiles by active sampling on Anasorb 747 and selected ion monitoring on a mass spectrometer equipped with a quadropole detector.
Abstract: There is a relationship between damp buildings and health complaints. Damp conditions in building constructions also favour the growth of micro-organisms. Growth of micro-organisms results in the production of volatile organic compounds, which has been shown to have an impact on Indoor-air monitored via a microbial volatile organic compound (MVOC) analysis. In order to widen the applicability of MVOC analysis, it is necessary to increase this analysis by including more volatiles. By active sampling on Anasorb 747 and selected ion monitoring on a mass spectrometer equipped with a quadropole detector, it is possible to determine these volatiles with sufficient accuracy in indoor air of non-industrial buildings.
TL;DR: In this article, a method employing supercritical fluid extraction (SFE) and GC coupled with microwave-induced plasma atomic emission spectrometry (MIP-AES) is presented for the determination of methylmercury in sediments.
Abstract: A method employing supercritical fluid extraction (SFE) and GC coupled with microwave-induced plasma atomic emission spectrometry (MIP–AES) is presented for the determination of methylmercury in sediments. Butylmagnesium chloride was used to derivatize the target compound to butylmethylmercury which is amenable to GC. Using a commercially available reference sediment (PACS-1, National Research Council of Canada) as the model sample, a factorial design was utilized to investigate the effect of three variables; density, temperature and flow rate, on the extraction efficiency. An extraction efficiency of 49 ± 0.5% could be obtained for a 37.5 min dynamic extraction, corresponding to 25 thimble volumes of supercritical CO2, and using purified support sand. Studies on the efficacy of SFE for another sediment matrix as a function of time have also been undertaken. Repeated pressure reductions in combination with support sand were found to increase the extraction efficiency of methylmercury from PACS-1 but not from a sediment issued by the Community Bureau of Reference (BCR) as part of an interlaboratory comparison. For PACS-1 this resulted in an increase in the average extraction efficiency to 96% for duplicate determinations following 50 thimble volume sweeps. Distillation was used as a reference method for isolation of methylmercury from sediments. Parallel extractions of the BCR sediment, using GC–MIP–AES for the final determination, gave results that were in good agreement and corresponded well with data submitted during the intercomparison exercise. The detection limit for the methylmercury in sediment using the described SFE GC–MIP–AES method is estimated to be 0.1 ng g–1 based on a 20 µl injection, 0.5 g of sample and three times the blank level. It is proposed that the co-extracted sulfur from the sediment mediates the transport of methylmercury and, to some extent, inorganic mercury from the sediments. This is supported by the strong correlation between the concentrations of butylmethylmercury and dibutylsulfide found in the toluene extract. Using a stable isotope tracer, 199Hg, and ICP-MS, evidence for the spurious formation of methylmercury during SFE under certain conditions is also presented.
TL;DR: A definition of fitness for purpose based on minimal expected loss is proposed, which enables one to develop optimal strategies for apportioning resources between sampling and analysis, and for balancing technical costs with end-user losses due to error.
Abstract: Fitness for purpose is the principle universally accepted among analytical scientists as the correct approach to obtaining data of appropriate quality. Yet few analytical scientists or end-users of data are in a position to specify exactly what quality of data is required for a specific task. A definition of fitness for purpose based on minimal expected loss is proposed in this paper. This idea enables one to develop optimal strategies for apportioning resources between sampling and analysis, and for balancing technical costs with end-user losses due to error.
TL;DR: Two sequential extraction schemes for speciation of Cu, Cr, Pb, Ni and Zn in sewage sludges yielded similar performance when extraction efficiencies were compared but matrix effects caused by concomitants were less pronounced in the BCR scheme in comparison with the Tessier scheme.
Abstract: Two sequential extraction schemes were employed for speciation of Cu, Cr, Pb, Ni and Zn in sewage sludges: the conventional Tessier scheme and the sequential extraction scheme proposed by the European Communities Bureau of Reference (BCR). Both sequential extraction schemes were compared in terms of operation time, matrix effects and extraction efficiency. Two sludge samples collected from an urban wastewater processing plant at different seasons were analysed by FAAS for total contents and for extractable metals present in each fraction. Partitioning patterns were obtained for each metal so that metal mobility could be predicted. Both sequential extraction schemes yielded similar performance when extraction efficiencies were compared but matrix effects caused by concomitants were less pronounced in the BCR scheme in comparison with the Tessier scheme.
TL;DR: An analytical method based on a semi-continuous hydride generator coupled on-line with a gas chromatograph and mass spectrometric detectro was developed and used for the identification of hydrides-forming antimony compounds as discussed by the authors.
Abstract: An analytical method based on a semi-continuous hydride generator coupled on-line with a gas chromatograph and mass spectrometric detectro was developed and used for the identification of hydride-forming antimony compounds. This method allows for the characterization of compounds based on their retention times and mass spectral data. Organoantimony compounds were identified to be present in extracts of a freshwater plant, namely pondweed (Potamogetan pectinatus). This is the first time that such compounds have been detected in samples of biological origin. The problem of organostibine molecular rearrangements which have been reported to occur during the hydride generation process was also investigated. An experimental procedure is described that allows for the elimination of such rearrangements.
TL;DR: The photoactive supermolecule "lumophore-spacer-receptor" is shown to be capable of considerable tuning and growth to satisfy the requirements of a versatile sensing system as mentioned in this paper.
Abstract: The photoactive supermolecule ‘lumophore–spacer–receptor’ is shown to be capable of considerable tuning and growth to satisfy the requirements of a versatile sensing system.
TL;DR: An overview of methods for the study of complex biological processes by using micro-column liquid chromatography-electrospray ionization tandem mass spectrometry is provided in this article.
Abstract: An overview is provided of methods for the study of complex biological processes by using micro-column liquid chromatography-electrospray ionization tandem mass spectrometry. Procedures discussed include electrospray ionization, micro-column liquid chromatography, tandem mass spectrometry, tandem mass spectra data interpretation for peptides, and database searching with mass spectral data. Several problems in immunology are discussed to illustrate this approach.
TL;DR: In this paper, an on-line amalgamation trap was constructed for the collection of mercury species separated by capillary GC for detection by microwave-induced plasma atomic emission spectrometry, and the trap allowed the determination of dimethylmercury in condensate down to a detection limit of 0.24 µg l−1 and derivatized (butylated) monomethyl and inorganic mercury down to 0.56 µgl−1 in natural gas condensates.
Abstract: An on-line amalgamation trap was constructed for the collection of mercury species separated by capillary GC for detection by microwave-induced plasma atomic emission spectrometry. For direct measurement of the column eluate, the detection limits for mercury species in natural gas condensate are elevated because of background interference from carbon compounds passed to the plasma at the same time. Carbon compounds give rise to emission that spectrally interferes with the signal from the mercury detector and can overload the plasma discharge, reducing the excitation capability. With an amalgamation trap, mercury can be selectively collected from the column eluate and subsequently passed to the plasma in a flow of pure helium. By removing the carbon background emission, the trap allows the determination of dimethylmercury in condensate down to a detection limit of 0.24 µg l–1 and derivatized (butylated) monomethyl and inorganic mercury down to a detection limit of 0.56 µg l–1 in natural gas condensate. Use of the trap is compared with some existing determination methods for mercury species in condensate and other samples. Solid-phase micro-extraction is used for dimethylmercury, which gives a poorer detection limit of around 20 µg l–1 because the analyte mass collected is small compared with liquid sample injection. Following derivatization, samples are diluted for direct methylbutylmercury and dibutylmercury determination, corresponding to methylmercury and inorganic mercury. Dilution ensures a reasonably stable background for mercury signals. Again, poorer detection limits of 3.1 and 2.3 µg l–1, respectively, are obtained owing to the reduced analyte mass. The trap permits the injection of untreated condensate, or condensate reacted with butylmagnesium chloride, into the gas chromatograph without the need for dilution or sample clean-up.
TL;DR: In this paper, an extract clean-up step was introduced to eliminate or decrease interference from 2-nitrobenzaldehyde (NBA) in the HPLC-UV determination of NPAOZ.
Abstract: Studies undertaken using radiolabelled furazolidone have demonstrated the covalent binding of residues of the drug to cellular protein in vivo. A portion of these bound residues and those formed by furaltadone, a related nitrofuran drug, possess intact side-chains, 3-amino-2-oxazolidinone (AOZ) and 5-morpholinomethyl-3-amino-2-oxazolidinone (AMOZ), respectively. These side-chains have molecular characteristics in common with the parent compounds and may be released from liver tissue under mild acidic conditions. Derivatization with 2-nitrobenzaldehyde (NBA) serves to isolate the released side-chains and the derivatives NPAOZ and NPAMOZ are chromophoric, thereby permitting UV detection. This paper reports the introduction of an extract clean-up step to the existing procedure which eliminates or decreases interference from NBA in the HPLC–UV determination of NPAOZ. The modified procedure was also applied to the determination of AMOZ. The development of an LC–MS method for the quantitative and confirmatory determination of AOZ and AMOZ extracted and derivatized according to the same procedure as that for HPLC–UV is described. The methods were validated for AOZ and AMOZ in fortified (intra-and inter-assay studies) and incurred (inter-assay studies) pig liver samples. The limit of determination for fortified control liver samples was 5 ng AOZ g–1 and 10 ng AMOZ g–1 by HPLC–UV and 10 ng AOZ or AMOZ g–1 by LC–MS. In addition, a study to determine the ratio of released AOZ to the total bound residues present in incurred liver samples from pigs treated with furazolidone is described.
TL;DR: In this paper, a method was described whereby the resistance of electrodeposited polymer films can be measured as they are grown, enabling films of pre-determined resistances to be produced.
Abstract: The sensitivity and response speed of the resistance changes of conducting polymer films when exposed to gases is increased if the film is thin and if the measurement of the response excludes the polymer-to-metal contact resistance at the electrodes of the sensor. A method is described whereby the resistance of electrodeposited films can be measured as they are grown, enabling films of pre-determined resistances to be produced. The principal cause of film resistance variation is differences in the time taken to bridge the gap between electrodes. The experiments reported here involve four-terminal measurements, which enable the effect of electrode contact resistance to be estimated and eliminated. The contact resistance between the polymer and metal electrodes is found to be up to 50% of the total resistance of the sensor, and less affected by exposure to a gas than is the polymer resistance. Four-terminal measurements of resistance therefore give the greatest sensitivity.
TL;DR: In this paper, an IR fiber optic sensor which operates in the 4-16 µm wavelength region has been developed for the in-situ monitoring of chlorinated hydrocarbons and pesticides in water.
Abstract: An IR fibre optic sensor which operates in the 4–16 µm wavelength region has been developed for the in-situ monitoring of chlorinated hydrocarbons and pesticides in water. The sensing element consists of a silver halide (AgClxBr1–x) optical fibre, coated with a polymer which both enriches the analyte in the evanescent wave region of the fibre and, when thick polymer coatings are used, minimizes water interference in the IR absorption. Using trichloroethylene and alachlor as representative pollutants, evanescent wave spectrometry in the mid-IR region is shown to provide good performance down to single ppm levels. Furthermore, it is shown that the technique can be applied to multi-analyte samples.
TL;DR: In this article, the performance of an optode in measurements of low concentrations of dissolved CO2 was characterized, and the method of lipophilic extraction of ion pairs into the membrane phase according to Weigl and Wolfbeis was applied to the fluorescent pH indicator hydroxypyrenetrisulfonic acid together with the quaternary ammonium base tetraoctylammonium hydroxide.
Abstract: The performance of an optode in measurements of low concentrations of dissolved CO2 was characterized. The method of lipophilic extraction of ion pairs into the membrane phase according to Weigl and Wolfbeis was applied to the fluorescent pH indicator hydroxypyrenetrisulfonic acid together with the quaternary ammonium base tetraoctylammonium hydroxide. The membrane solution was applied directly to an acrylic optical fibre of 1 mm diameter. Solutions of NaHCO3 were used as standards and H2CO*3 concentrations calculated. The dynamic range for the detection of H2CO*3 was 4 × 10–6–1 × 10–2 mol l–1. Response times depended on the concentration range and whether the concentration was increased or decreased: τ90% was 6 min. The sensor was found to show an increasing susceptibility to temperature at the low end of the calibration graph for H2CO*3. The use of a low concentration of base in the membrane resulted in the desired detection limit, but also in a lifetime limited to 1 d.
TL;DR: Examination of workers' exposures to 'total' and inhalable aerosol in the workplaces of several industries in several countries and proposed options for how such information might influence the setting of future occupational exposure limits are examined.
Abstract: Since the late 1970s, there has been considerable discussion about describing human aerosol exposure in terms of a scientific criterion based on the efficiency with which particles are inhaled through the nose and/or mouth during breathing. As international agreement on the quantitative form of this criterion has emerged, progress is quickening towards workplace and environment aerosol standards in which the current ‘total aerosol’ approach will be replaced by one based on ‘inhalability’. Wind tunnel investigations of a range of personal samplers currently used in workplaces for sampling ‘total’ aerosol have shown that many of these are not adequate for collecting the inhalable fraction. Such experimental evidence is supported by considerations of the physical sampling characteristics of the various samplers. Studies have been conducted to investigate workers' exposures to ‘total’ and inhalable aerosol in the workplaces of several industries in several countries, using side-by-side sampling in which participating workers wear two samplers, one for ‘total’ aerosol and the other for inhalable aerosol. The results from the several hundred sample pairs taken so far show that the level of exposure based on inhalable aerosol consistently exceeds that for ‘total’ aerosol. The observed ratios between the inhalable and ‘total’ aerosol exposures range from 1.2 to > 3, tending to be greater for workplaces where the aerosol is expected to be coarser. Such results may be used to assess the impact on industry of new limit values based on inhalable aerosol. It is clear that measured levels of exposure will tend to rise, so that there will be generally increased proportions of exposure measurements where levels will come close to, or exceed, current exposure limits. Those proportions may be greater still if new, lower limit values for ‘total’ aerosol currently under consideration for some substances are implemented. This paper examines these issues by reference to examples of exposure data taken from a range of industries and proposes options for how such information might influence the setting of future occupational exposure limits.
TL;DR: In this paper, a non-linear reaction/diffusion equation describing the substrate transport and reaction kinetics within the polymer film is formulated and approximate analytical solutions for the substrate concentration profiles and corresponding current responses are developed.
Abstract: The theoretical analysis of the steady-state amperometric response for a polymer-modified electrode system whcih exhibits Michaelis–Menten kinetics is discussed. In particular, the interplay between substrate diffusion within the polymer matrix and substrate reaction at the catalytic polymer sites is examined. A non-linear reaction/diffusion equation describing the substrate transport and reaction kinetics within the film is formulated and approximate analytical solutions for the substrate concentration profiles and corresponding current responses are developed. Four distinct limiting cases are developed and are represented schematically in a kinetic case diagram. The theoretical analysis is extended to consider the complicating situation of substrate diffusion in the Nernst diffusion layer adjacent to the polymer film. The allied problem of the response of a potentiometric sensor exhibiting Michaelis–Menten kinetics is also examined. The theoretical model developed in the paper is validated by examining the electro-oxidation of dopamine, adrenaline and noradrenaline at surfactant-doped polypyrrole-modified electrodes. Good agreement between the amperometric current response predicted from the theoretical model and the current response obtained experimentally from batch amperometry is obtained. Non-linear least-squares analysis of the batch amperometric data in tandem with the theoretical expression derived for the steady-state current response produces reasonable values for the Michaelis constant, Km, the catalytic rate constant, Kc, and the substrate diffusion coefficient, Ds, for each of the three catecholamine substrates examined.
TL;DR: Two simple, rapid and selective spectrophotometric procedures were developed for the determination of amoxicillin and cefadroxil and compared favourably with those obtained with other reported methods.
Abstract: Two simple, rapid and selective spectrophotometric procedures were developed for the determination of amoxicillin and cefadroxil. The methods are based on the selective oxidation of the drugs with N-bromosuccinimide or N-chlorosuccinimide in an alkaline medium to give an intense yellow product (λmax= 395 nm). The reaction conditions were studied and optimized. The reactions obey Beer's law over the range 1–20 µg ml–1 for the two drugs with the two reagents. Interferences from other antibiotics, additives and common degradation products were investigated. The proposed methods were applied to the analysis of pharmaceutical formulations containing amoxicillin, either alone or in combination with potassium clavulanate or flucloxacillin. They were also applied to the analysis of some cefadroxil dosage forms. The results obtained compared favourably with those obtained with other reported methods.