| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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| 4. |
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| 5. |
- 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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| 6. |
- Jönsson, Bo A, et al.
(författare)
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Determination of cyclic organic acid anhydrides in air using gas chromatography .1. A review
- 1996
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Ingår i: Analyst. - 1364-5528. ; 121:9, s. 1279-1284
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Forskningsöversikt (refereegranskat)abstract
- Gas chromatographic methods for the determination of cyclic organic acid anhydrides (OAAs) in industrial air are reviewed. The OAAs discussed are phthalic, hexahydrophthalic, methylhexahydrophthalic, tetrahydrophthalic, methyltetrahydrophthalic, trimellitic, maleic, and octenylsuccinic anhydride. Solid sorbent sampling methods, using Amberlite XAD-2 or Tenax, are used for sampling of OAA vapour. These methods are easy to use, have simple work-up procedures and sample the anhydrides as such. However, many OAAs are reactive compounds and losses during storage should be considered. Sampling of OAAs in mixed exposure of particles and vapour are performed by either bubblers or impingers with aqueous sampling solutions or by filters in series with solid sorbent tubes. It can be assumed that non-polar filter samples an OAA as such. Hence these methods are easy to use, but losses during storage must be considered. Bubblers/impingers convert the OAAs into the corresponding acids and glass-fibre filters do the same, at least in part. The acids are stable on storage but a derivatization must be performed before GC analysis. Detection methods used for the analysis are flame ionization detection (FID), electron-capture detection (ECD) and MS using electron impact or negative-ion chemical ionization. Typical detection limits for determinations of OAAs as such are 0.1 µg of OAA per sample using FID and an order of magnitude better using ECD or MS. For determination of the esters from the corresponding OAAs using MS, the detection limits are better than 0.01 µg of OAA per sample. Precisions are normally better than 10%.
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| 7. |
- Jönsson, Bo A, et al.
(författare)
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Determination of cyclic organic acid anhydrides in air using gas chromatography .2. Sampling and determination of hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, tetrahydrophthalic anhydride and octenylsuccinic anhydride
- 1996
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Ingår i: Analyst. - 1364-5528. ; 121:9, s. 1285-1290
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Tidskriftsartikel (refereegranskat)abstract
- Methods for sampling and determination of four organic acid anhydrides are described. The methods were validated in a standard atmosphere and in the work environment. Hexahydrophthalic anhydride (HHPA), methylhexahydrophthalic anhydride (MHHPA), tetrahydrophthalic anhydride (THPA) and octenylsuccinic anhydride (OSA) were sampled using Tenax and Amberlite XAD-2 solid sorbents and determined by GC with flame ionization detection (FID) after elution. The precision was normally better than 10% but for OSA it was up to 19%. The detection limits were 0.1 µg per sample. MHHPA, THPA and OSA were also sampled using bubblers containing aqueous sampling solutions. MHHPA and THPA was derivatized with pentafluorobenzyl bromide (PFBBr) and determined by GC with MS detection. OSA was derivatized by methanol with boron trifluoride catalysis and determined by GC–FID. The precisions for MHHPA and THPA were 4 and 8%, respectively, and the detection limit was < 0.005 µg per sample. The precision for OSA was up to 58% and the detection limit was 0.2 µg per sample. HHPA and MHHPA were also sampled on glass-fibre filters, derivatized with PFBBr, and determined by GC–MS with good results. However, further validations of the filter methods are needed.
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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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