| 1. |
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| 2. |
- Dennison, MJ, et al.
(författare)
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Direct monitoring of formaldehyde vapour and detection of ethanol vapour using dehydrogenase-based biosensors
- 1996
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Ingår i: The Analyst. - : Royal Society of Chemistry. - 0003-2654 .- 1364-5528. ; 121:12, s. 1769-1773
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Tidskriftsartikel (refereegranskat)abstract
- Biosensors capable of directly detecting low levels of formaldehyde and ethanol vapour were constructed, Both biosensors are based on dehydrogenase enzymes which produce reduced nicotinamide adenine dinucleotide as part of the oxidation of formaldehyde and ethanol, The enzymes were immobilized in a reverse micelle medium which did not dehydrate significantly over time, and allowed direct gas-phase monitoring, A screen-printed electrode was used as transducer. Formaldehyde and ethanol vapour partitioned into the reverse micelle media, where it was acted upon by the relevant enzyme, Reduced nicotinamide adenine dinucleotide was oxidized at the working electrode at a potential of 800 mV versus an Ag/AgCl reference electrode, Formaldehyde could be measured over the concentration range 1 ppb-1.3 ppm and ethanol could be detected over the range 50-250 ppm.
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| 3. |
- Emteborg, Håkan, et al.
(författare)
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Determination of methylmercury in sediments using supercritical fluid extraction and gas chromatography coupled with microwave-induced plasma atomic emission spectrometry
- 1996
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Ingår i: The Analyst. - 0003-2654 .- 1364-5528. ; 121:1, s. 19-29
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Tidskriftsartikel (refereegranskat)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.
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| 4. |
- Enger, Jonas, et al.
(författare)
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Laser-induced fluorescence in a graphite furnace as a sensitive technique for assessment of traces in North Arctic atmospheric aerosol samples
- 1995
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Ingår i: The Analyst. - : Royal Society of Chemistry. - 0003-2654 .- 1364-5528. ; 120:3, s. 635-641
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Tidskriftsartikel (refereegranskat)abstract
- An improved version of the highly sensitive laser-based spectroscopic trace-element detection technique, laser-induced fluorescence in a graphite furnace, LIF-GF (often also referred to as laser-excited atomic fluorescence spectrometry in electrothermal atomizer, ETA-LEAFS) has been used to assess the trace-element content of Al and Pb in size-fractionated aerosol samples from the Norwegian Arctic. The ordinary LIF-GF technique has been modified for improved selectivity by the incorporation of a multi-channel intensified CCD detector (ICCD) which mikes constant monitoring of various background signals possible (scattered laser light, concomitant fluorescence light, and black body radiation). It is shown that the sensitivity and selectivity of the LIF-GF-ICCD technique is sufficient for efficient detection of the trace contents of Al and Pb in dissolved aerosol samples from the Norwegian Arctic (0-75 pg for each furnace heating). The Al and Pb concentrations in air from Ny Alesund, Svalbard, at the time of sampling (March-April 1992) were found to be 1-50 ng m-3.
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| 5. |
- Gadomska, J, et al.
(författare)
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Mass transport-controlled steady-state currents for methanol in a flow injection system
- 1996
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Ingår i: ANALYST. - : ROYAL SOC CHEMISTRY. - 0003-2654. ; 121:12, s. 1869-1871
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Tidskriftsartikel (refereegranskat)abstract
- It is known that undiluted methanol can give mass transport-controlled steady-state oxidation currents at Pt microelectrodes. In the present study, the steady-state currents were examined under flow injection conditions. It was found that the methanol ox
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| 6. |
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| 7. |
- Johansson, Ursula, et al.
(författare)
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Isotopic exchange of kaolinite hydroxyl protons: a diffuse reflectance infrared Fourier transform spectroscopy study
- 1998
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Ingår i: The Analyst. - 0003-2654 .- 1364-5528. ; 123:4, s. 641-645
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Tidskriftsartikel (refereegranskat)abstract
- Specific surface reactions on kaolinite were investigated by deuterium exchange of the hydroxyl protons of kaolinite, The kaolinite samples were reacted with deuterium oxide for 48 h and 2.5 and 5 weeks, at various pH values (3, natural and 8) and at different temperatures (ambient, and 30, 60 and 100 degrees C), Analyses were performed using diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The spectral results show that it is very difficult at room temperature to exchange the hydroxyl protons isotopically with deuterons at the surface of kaolinite, The temperature and the reaction time must be increased for successful exchange. It was found that the most suitable temperature for isotopic exchange was 60 degrees C. The pH did not significantly influence the deuteration, Only at high pH were changes of the OD bands in the DRIFT spectra observed, This study shows that it is possible to deuterate kaolinite without using intercalation. All three types of hydroxyl protons from the inner, inner surface and edge were exchanged.
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| 8. |
- Lind, Pernilla, et al.
(författare)
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Albumin adducts in plasma from workers exposed to toluene diisocyanate
- 1997
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Ingår i: Analyst. - : Royal Society of Chemistry (RSC). - 1364-5528. ; 122:2, s. 151-154
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Tidskriftsartikel (refereegranskat)abstract
- Desalted plasma from a 2,4- and 2,6-toluene diisocyanate (2,4- and 2,6-TDI) exposed worker at a factory producing flexible polyurethane foam was separated and fractionated into 200 fractions using ion-exchange chromatography followed by a gel-filtration separation and fractionation into 59 fractions. The corresponding amines (to the isocyanates), 2,4- and 2,6-toluenediamine (2,4- and 2,6-TDA), were determined in each fraction after sulfuric acid hydrolysis as pentafluoropropionic anhydride derivatives by capillary gas chromatography and chemical ionisation mass spectrometry monitoring negative ions. The ion exchange fractions containing TDA (81-115) were added together and the solution was separated and fractionated on the gel-filtration column. The fractions 81-115 contained 84 and 72% of 2,4- and 2,6-TDA, respectively, as compared to the unfractionated plasma. The gel filtration fractions 22-27 contained 107 and 119% of 2,4- and 2,6-TDA, respectively, as compared to the amounts in the ion exchange fractions (81-115). Agarose gel-electrophoresis and electroimmunoassay demonstrated that albumin, 2,4- and 2,6-TDA co-eluted in both ion-exchange and gel-filtration chromatography. Quantitative determination of albumin, 2,4- and 2,6-TDA also demonstrated that these components co-eluted using albumin-immunosorption chromatography. In addition, studies of affinity isolated IgG revealed that this fraction was devoid of 2,4- and 2,6-TDA. These results indicate that albumin is the major receptor molecule for 2,4- and 2,6-TDI in blood plasma and that these isocyanates form covalent bondings with albumin.
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| 9. |
- Liu, Wenxin, et al.
(författare)
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A flexible method of carbonate determination using an automatic gas analyzer equipped with an FTIR photoacoustic measurement chamber
- 1999
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Ingår i: The Analyst. - 0003-2654 .- 1364-5528. ; 124:3, s. 361-365
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Tidskriftsartikel (refereegranskat)abstract
- A Fourier transform infrared spectrometer was employed to determine automatically the total inorganic carbonate (TIC) in solids and waters, based on active photoacoustic absorption of infrared light by carbon dioxide. A 2.0 l reactor, connected to the spectrometer, is immersed in water-bath at 20 °C. After purging with pure N2, 5 ml of 0.5 mol l–1 HClO4 are injected into 50 ml of solid suspension or solution with continuous stirring. The specific absorption of infrared light by the CO2 evolved induces corresponding fluctuations of temperature and pressure in a measurement chamber. Accordingly, photoacoustic signals, with frequencies dependent on the absorbed wavelengths, are generated and measured by the chamber microphones in the form of an absorption spectrum and concentration. For solids, the method exhibits a linear response up to 120 mg of CaCO3 with a detection limit of 0.02 mg; in the case of waters, these figures of merit are 36.4 mmol l–1 and 3 µmol l–1 NaHCO3, respectively. Since proton consumption by TIC in clay minerals may commonly influence the evaluation of surface acid–base properties, the methodology was applied to determine TIC in three natural illite samples of different origins. In addition, some potential interferences and modifications of this method are discussed.
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| 10. |
- Loughran, MG, et al.
(författare)
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Ammonium ion requirement and stability of methanol dehydrogenase TTF TCNQ electrodes
- 1996
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Ingår i: The Analyst. - : Royal Society of Chemistry. - 0003-2654 .- 1364-5528. ; 121:11, s. 1711-1715
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Tidskriftsartikel (refereegranskat)abstract
- The ammonium ion requirement and stability of quinoprotein methanol dehydrogenases were investigated with a view to incorporating them in enzyme electrodes for alcohol. This involved consideration of the effect of temperature and polyelectrolytes on enzyme stability. A packed cavity electrode was constructed using the organic conducting salt TTF-TCNQ (tetrathiafulvalene-tetracyanoquinodimethane). Methanol dehydrogenase isolated from Paracoccus denitrificans was more stable than the enzyme isolated from Methylophilus methylotrophus and was successfully used for repeated assay in packed cavity electrodes without significant loss in current output. These investigations also showed that, contrary to suggestions in the literature, ammonium ions are necessary for efficient re-oxidation of methanol dehydrogenase at the organic conducting salt electrode.
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| 11. |
- Papantoni, Margareta, et al.
(författare)
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Trace enrichment of metals using a supported liquid membrane technique
- 1995
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Ingår i: Analyst. - 0003-2654. ; 120:5, s. 1471-1477
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Tidskriftsartikel (refereegranskat)abstract
- The supported liquid membrane technique offers new possibilities for analytical enrichment, field sampling and speciation. The possibility of using the technique for the enrichment of metals in a flow system with off-line atomic absorption spectrometry in the final analysis step is outlined. Five metals (Cu, Cd, Co, Ni and Zn) have been used as model substances and different approaches to transport metals across the membrane are demonstrated. In one system 8-hydroxyquinoline was used as complexing agent in the sample (donor) solution. In a second system potassium thiocyanate was used in the donor solution and an extradant (Aliquat-336) in the membrane liquid. In a third system 8-hydroxyquinoline was used in the donor solution and Aliquat-336 in the membrane liquid. The parameters important for analytical enrichment are considered. These include factors for determining the extraction efficiency, the possibility of carry-over effects, matrix dependence and long-term membrane stability. The memory effects were below 2% and high concentrations of humic acids or salts did not interfere in the analysis. The long-term stability using di-n-hexyl ether in the membrane was 1-2 weeks and with the extractant Aliquat-336 incorporated in the membrane liquid it was 4 d. Determination of metals at levels <1 ppb was possible. The limiting factor for the determination at lower concentrations at present is the metal contamination in the reagents used.
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| 12. |
- Sarkar, P, et al.
(författare)
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Screen-printed amperometric biosensors for the rapid measurement of L- and D-amino acids
- 1999
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Ingår i: The Analyst. - : Royal Society of Chemistry. - 0003-2654 .- 1364-5528. ; 124:6, s. 865-870
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Tidskriftsartikel (refereegranskat)abstract
- Screen-printed three-electrode amperometric sensors incorporating L- and/or D-amino acid oxidase for the general purpose measurement of L- or D-amino acids is described. The working electrode incorporates rhodinised carbon, to facilitate hydrogen peroxide oxidation at a decreased operating potential, and immobilised enzyme. The devices responded to all 20 common L-amino acids and all of the D-amino acids examined, the exceptions being L- and D-proline. Linear response profiles were observed for L-leucine, L-glycine and L-phenylalanine with limits of detection of 0.47, 0.15 and 0.20 mM respectively. The devices were reproducible and exhibited stability over a 56 d test period. The biosensor compares favourably with a standard photometric amino acid test and was used to monitor milk ageing effects, The assay is cheap, simple to perform and rapid, requiring only buffer-electrolyte and a small sample volume.
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| 13. |
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| 14. |
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| 15. |
- Xie, Bin, et al.
(författare)
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Development of an integrated thermal biosensor for the simultaneous determination of multiple analytes
- 1995
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Ingår i: The Analyst. - 0003-2654. ; 120:1, s. 155-160
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Tidskriftsartikel (refereegranskat)abstract
- A flow injection thermal microbiosensor was designed for the simultaneous determination of multiple analytes. The biosensor consisted of five thin-film thermistors which were located along a single microchannel. The device was fabricated on a quartz chip by micromachining. The feasibility of employing this system for the detection of two independent enzyme reactions was demonstrated using two different pairs of enzymes, urease-penicillinase and urease-glucose oxidase. The enzymes were immobilized on agarose beads, which were then sequentially packed into distinct regions of the microchannel. Using this method, samples containing urea mixed with penicillin V or with glucose were simultaneously analysed. Linear ranges of up to 20 mmol l-1 urea, 40 mmol l-1 penicillin V and 8 mmol l-1 glucose (saturated with O2) were obtained using a flow rate of 30 μl min-1 and a sample volume of 20 μl. The relative standard deviations for urea and penicillin V assays were 1.13 and 2.42% for the first 100 samples and 1.17 and 2.78% for 200 samples, respectively. The sensor is capable of analysing 25 samples per hour.
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