| 1. |
- Larsson, Henrik, et al.
(författare)
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Charge propagation in [Os(bpy)2(PVP)xCl]Cl polymers. An example of mean field behavior in a system with constrained diffusion of redox sites?
- 1995
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Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier. - 0022-0728 .- 1873-2569. ; 381:1-2, s. 133-142
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Tidskriftsartikel (refereegranskat)abstract
- Chronocoulometry and impedance spectroscopy were used to study the dynamics of charge transport in a series of methylated [Os(bpy)(2)(PVP)(x)Cl]Cl polymers (PVP = poly(4-vinylpyridine); bpy = 2,2'-bipyridine; 5 less than or equal to x less than or equal to 40) which were deposited as thin firms on glassy carbon electrodes. Apparent charge propagation diffusion coefficients D-app were of the order of 10(-8) cm(2) s(-1) and were approximately linearly dependent on the total concentration of redox sites but independent of the ratio of oxidized to reduced centres present in a particular coating. Attempts were made to explain these observations in terms of a recent theory of charge transport appropriate for systems in which the redox sites are permanently attached to the polymer chains. It was found that the concentration dependence and magnitude of D-app could be explained satisfactorily by a mean field model of charge propagation.
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| 2. |
- Larsson, Henrik, et al.
(författare)
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Electron transport in quaternized poly(4-vinylpyridine) films containing pentacyanoferrate(II/III) on electrodes. The influence of the binding type of the electroactive complex
- 1992
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Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier. - 0022-0728 .- 1873-2569 .- 1572-6657. ; 336:1-2, s. 263-279
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Tidskriftsartikel (refereegranskat)abstract
- This study is an attempt to investigate how charge transport in thin redox polymer films spin-coated onto glassy carbon electrode surfaces is affected by the way in which the electroactive group is bound to the polymeric matrix. Two different redox polymers based on methylated and cross-linked poly(4-vinylpyridine) and pentacyanoferrate(II/III) have been synthesized. In the first case, an anionic complex formed by coordinating pyridine to pentacyanoferrate(II) was electrostatically bound to the methylated pyridine groups in the polymer matrix. In the other case, pentacyanoferroate(II) was coordinated directly to unmethylated pyridine groups in the partly methylated polymer film. The film thicknesses were estimated with ellipsometric measurements. Their electrochemical characteristics were investigated using cyclic voltammetry, chronocoulometry and impedance spectroscopy. The apparent charge-transport diffusion coefficient D(app) was almost two orders of magnitude greater in the ion-exchange polymer than in the redox polymer with coordinatively bound electroactive groups. The temperature dependence of D(app) was evaluated using Arrhenius plots.
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| 3. |
- Larsson, Henrik
(författare)
-
Ellipsometric determinations of the thicknesses of dry and electrolyte-immersed poly(4-vinylpyridine) films containing coordinated light-absorbing [Os(bpy)2pvpCl]2+/+ redox groups
- 1994
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Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier. - 1572-6657 .- 1873-2569. ; 365:1-2, s. 229-237
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Tidskriftsartikel (refereegranskat)abstract
- Ellipsometry has been used to measure the dimensions of quaternized poly(4-vinylpyridine) films containing [Os(bpy)2pvpCl]2+/+ redox groups on glassy carbon electrodes. Film thicknesses and complex refractive indices were deduced using molar absorptivities obtained from photometry or a combination of photometry and cyclic voltammetry. The precision in the film thicknesses was estimated using data obtained from thick and thin films with the same polymer + redox group compositions and from data recorded at 60-degrees and 70-degrees angles of incidence of 633 nm laser light. The effects of errors in the experimentally determined molar absorptivity of the redox groups on film thickness were also assessed. The results of this study suggest that reliable thicknesses can be obtained for both dry and electrolyte-swollen films, and that the presence of light-absorbing redox groups within coatings such as these presents no real obstacle for ellipsometric determinations.
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| 4. |
- Sharp, Michael, et al.
(författare)
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Studies of the temperature dependence of charge propagation rates in quaternized poly(4-vinylpyridine) polymers containing electrostatically bound and coordinated redox sites
- 1995
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Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier. - 0022-0728 .- 1873-2569. ; 386:1-2, s. 189-195
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Tidskriftsartikel (refereegranskat)abstract
- The activation parameters associated with charge propagation in a series of quaternized poly(4-vinylpyridine) polymers, which contained both electrostatically hound and coordinated redox sites and which were deposited as thin films on electrode surfaces, were derived from the temperature dependence of apparent charge transport diffusion coefficients. The values of the activation energies and entropies obtained are discussed in terms of models of charge transport that are appropriate for redox polymers in which physical displacements of the redox sites are either free or constrained.
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| 5. |
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| 6. |
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| 7. |
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| 8. |
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| 9. |
- Ademark, Pia, et al.
(författare)
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Hydrolytic properties of a beta-mannosidase purified from Aspergillus niger. J. Biotechnol. 75: 281-289.
- 1999
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Ingår i: Journal of Biotechnology. - 1873-4863. ; 75:2-3, s. 281-289
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Tidskriftsartikel (refereegranskat)abstract
- A β-mannosidase was purified to homogeneity from the culture filtrate of Aspergillus niger. A specific activity of 500 nkat mg−1 and a 53-fold purification was achieved using ammonium sulfate precipitation, anion-exchange chromatography, and gel filtration. The isolated enzyme has an isoelectric point of 5.0 and appears to be a dimer composed of two 135-kDa subunits. It is a glycoprotein and contains 17% N-linked carbohydrate by weight. Maximal activity was observed at pH 2.4–5.0 and at 70°C. The β-mannosidase hydrolyzed β-1,4-linked manno-oligosaccharides of degree of polymerization (DP) 2–6 and also released mannose from polymeric ivory nut mannan and galactomannan. The Km and Vmax values for p-nitrophenyl-β-Image-mannopyranoside were 0.30 mM and 500 nkat mg−1, respectively. Hydrolysis of Image-galactose substituted manno-oligosaccharides showed that the β-mannosidase was able to cleave up to, but not beyond, a side group. An internal peptide sequence of 15 amino acids was highly similar to that of an Aspergillus aculeatus β-mannosidase belonging to family 2 of glycosyl hydrolases.
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| 10. |
- Amine, A., et al.
(författare)
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A Microdialysis probe coupled with a miniaturized thermal glucose sensor for in vivo monitoring
- 1995
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Ingår i: Analytical Letters. - : Informa UK Limited. - 0003-2719 .- 1532-236X. ; 28:13, s. 2275-2286
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Tidskriftsartikel (refereegranskat)abstract
- A miniaturized thermal flow injection analysis biosensor has been coupled with a microdialysis probe for continuous subcutaneous glucose monitoring. Thermal biosensors are based on the principle of measuring the heat evolved during enzyme catalysed reactions. The system presented here consists of a miniaturized thermal biosensor with a small column containing coimmibolized glucose oxidase and catalase. The analysis buffer passes through the column at a flow rate of 60μL/min via an 1μL sample loop which is connected to a microdialysis probe. Invitro results showed constant permeability of the probe and stability of the biosensor response during 24 hours. The response time was 85 sec giving a sample rate of 42 samples/hour. During a load experiment, the glucose profile in a healthy volunteer was followed both in the subcutaneous tissue and blood using the microdialysis set-up proposed and comparing to blood glucose analyser.
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| 11. |
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| 12. |
- Andersson, Mikael, et al.
(författare)
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Characterization of the Chemical and Functional Stability of DEAE Sepharose Fast Flow
- 1993
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Ingår i: Process Biochemistry. - 1359-5113 .- 1873-3298. ; 28:4, s. 223-230
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Tidskriftsartikel (refereegranskat)abstract
- The release of amines from the ion-exchange groups in DEAE Sepharose® Fast Flow has been studied under static and column conditions. The leakage compounds have been identified and quantified by gas chromatography—mass spectrometry. It was shown that the main leakage product under acidic (pH 1) and basic conditions (pH 14) was N,N,N′,N′-tetraethylethylenediamine. Three other amines were also identified, namely N,N,N′-triethylethylenediamine, diethylaminoethanol and diethylamine. The leakage of amines from DEAE Sepharose Fast Flow treated at pH 1 or 14 for 672 h at 40°C corresponds to a reduction of only 1% of the total ion-exchange capacity.The functional stability of DEAE Sepharose Fast Flow was also studied by separation of a protein mixture during repeated cleaning-in-place treatments with 0·10 m HCl or 1·0 m NaOH. The separation behaviour was unaltered after the gel had been treated for a total contact time of 672 h with 0·10 m HCl or 1·0 m NaOH.The clearance of ethanol from a DEAE Sepharose Fast Flow column stored in a 20% ethanol aqueous solution was also studied.
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| 13. |
- Andersson, Martin
(författare)
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Process analytical methods for monitoring of the film coating on pharmaceutical pellets and tablets using NIR spectrometry and image analysis
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Pharmaceutical tablets and pellets are often covered with a coating. There is a need for methods that enable monitoring of the growth of such films during processing. Such analyses can be performed using process analytical chemical methods based on near infrared (NIR) diffuse reflectance spectrometry. It provides with analyses that take only ca. 8 seconds in total analysis time, including physical sampling. The use of chemometrics is the key to handle the complexity of the NIR spectra. The chemometric methods of principal component analysis (PCA) and partial least squares (PLS) were used to study and to calibrate NIR-spectra to the amount of coating. An at-line method using NIR-spectra for determination of the amount of coating of film applied on pharmaceutical tablets was developed. Limitations for quantitation of the film were determined by the 'information depth', ca 0.1 - 0.2 mm. Novel tools to determine the coating thickness and its variations on pharmaceutical pellets were based on image analysis and NIR diffuse reflectance spectrometry. Data from the images were used to predict variations in the release rate of the active substance due to geometrical variations. The image analysis was further used as a reference method for thickness measurements. Together with a theoretical film thickness growth model with physical relevance to underlying process mechanisms, an in-line process analytical chemical method based on NIR was enabled for analysis of the coating thickness on pharmaceutical pellets (RMSEP = 2.2 µm, range tested 0 - 50 µm). Indeed, such tools have not been combined previously, and through use of a multivariate batch calibration, the thickness values delivered from the NIR spectrometer became less disturbed by commonly varied process conditions. Additionally, variations in the coating thickness could be indicated by NIR . The spectral artefacts encountered for samples moving during acquisition of a scan were characterised in a separate study using multivariate methods. These artefacts could be detected by PCA.
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| 14. |
- Andersson, Mikael, et al.
(författare)
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The Influence of the Degree of Cross-linking, Type of Ligand and Support on the Chemical Stability of Chromatography Media Intended for protein Purification
- 1998
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Ingår i: Process Biochemistry. - 1359-5113 .- 1873-3298. ; 33:1, s. 47-55
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Tidskriftsartikel (refereegranskat)abstract
- The release of organic compounds from different liquid chromatography media in static conditions has been analysed with a total organic carbon (TOC) analyser. TOC results show that chemical stability increases with the degree of cross-linking in agarose beaded chromatography media and thus extend the working pH-range of the media. Of the unsubstituted chromatography media investigated, Sepharose® 6B, Sepharose CL-6B, Sepharose 4 Fast Flow, Sepharose 6 Fast Flow and Sepharose High Performance, the latter was the most stable medium. Sepharose High Performance releases only about 0·06% of its total carbon content after 1 week in 0·01 m HCl. Agarose beads are more stable to basic conditions (pH 14) compared with acidic conditions (pH 2). From UV spectroscopic and gel filtration results it was found that all Sepharose media release low amounts of 5-(hydroxymethyl)-2-furaldehyde and agarose fragments in acidic conditions. To investigate the effect of different ligands on chemical stability Q Sepharose 6 Fast Flow, DEAE Sepharose 6 Fast Flow, SP Sepharose 6 Fast Flow, CM Sepharose 6 Fast Flow, Phenyl Sepharose 6 Fast Flow, Octyl Sepharose 4 Fast Flow media were also studied under static conditions. In basic conditions it was found that all these chromatography media release carbon compounds to a higher extent than the unsubstituted Sepharose support. In addition, Hofmann elimination of Q and DEAE groups contributes to the decrease in the carbon content of the corresponding anion exchangers. During exposure to acidic conditions (pH 2) the release of carbon compounds was lower than the release from the support to which the ligands were coupled. The exceptions are Octyl Sepharose 4 Fast Flow and SP Sepharose 6 Fast Flow. In the case of Octyl Sepharose 4 Fast Flow, the ligand did not seem to influence chemical stability, whereas the SP group increases the degradation of the Sepharose support. In the case of SP Sepharose 6 Fast Flow the stability in acidic conditions can be improved by increasing the ionic strength. Anion exchangers based on different support polymers (agarose-, polystyrene-, methacrylate- and polyvinyl-based matrixes) were studied under static conditions. Agarose-based anion exchanger was the most stable in basic conditions (pH 14). In acidic conditions (pH 2) the chemical stability was about the same for many different anion exchangers.
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| 15. |
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| 16. |
- Andersson, Patrik, et al.
(författare)
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Ultraviolet absorption spectra of all 209 polychlorinated biphenyls evaluated by principal component analysis
- 1997
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Ingår i: Fresenius' Journal of Analytical Chemistry. - : Springer Science and Business Media LLC. - 0937-0633 .- 1432-1130. ; 357:8, s. 1088-1092
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Tidskriftsartikel (refereegranskat)abstract
- The ultraviolet absorption spectra of all 209 polychlorinated biphenyls (PCBs) were recorded in the range 200-300 nm and displayed two important absorption maxima, viz., the main-band, lambda(max) 200-225 nm, and the kappa-band, lambda(max) 245-265 nm. By utilising principal component analysis, substitution related spectral characteristics of the PCBs, underlying the main patterns of the spectra, were examined. Captured in the multivariate evaluation were e.g., the importance of chlorine atoms in ortho positions, determining the intensity and existence of the kappa-band, chlorine substitution in para-para position, and the total number of chlorine atoms. The measured UV-spectra of all 209 polychlorinated biphenyls provide important physico-chemical descriptors for use in future quantitative structure-activity and structure-property relationship (QSAR/QSPR) studies.
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| 17. |
- Appelblad, Patrik, et al.
(författare)
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Determination of C-21 ketosteroids in serum using trifluoromethanesulfonic acid catalyzed precolumn dansylation and 1,1’-oxalyldiimidazole postcolumn peroxyoxalate chemiluminescence detection
- 1998
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Ingår i: Analytical Chemistry. - Washington : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 70:23, s. 5002-5009
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Tidskriftsartikel (refereegranskat)abstract
- A new procedure for the quantitation of C-21 ketosteroids using trifluoromethanesulfonic acid-catalyzed precolumn dansylation and coupled column liquid chromatographic separation, followed by postcolumn 1,1‘-oxalyldiimidazole peroxyoxalate chemiluminescence detection is presented. In the simultaneous optimization of chromatographic resolution and chemiluminescence intensity, a coupled column chromatographic system and a stopped-flow system were used. An eluent containing 20 mM phosphate buffer at pH 6.7 accomplished an efficient separation of 3α-hydroxy-5β-pregnan-20-one from a mixture containing 10 C-21 ketosteroids. Phosphate buffer also proved to be the most advantageous, among the six buffers tested, for sensitive detection. Experimental design and multivariate data analysis were used to characterize and optimize the postcolumn reaction chemistry in the chromatographic system. A valid full factorial design with excellent predictability showed that the flow rates for both 1,1‘-oxalyldiimidazole and hydrogen peroxide were the factors most strongly affecting the sensitivity of the system. The theoretical plate numbers were above 11 000 for all 10 dansylated ketosteroids. The 3σ detection limit estimated from 3α-hydroxy-5β-pregnan-20-one calibration curve data was 1.6 pmol (n = 4, 125 μL injected) and spiked serum containing 0−74 pmol of this compound showed overall recoveries of 73 ± 9% (n = 12). Quantitation of 3α-hydroxy-5β-pregnan-20-one was finally carried out on 45 serum samples and the results compared to those from a radioimmunoassay (RIA) method. The data acquired with the procedure described in this work compare well with the results from RIA, which confirms the reliability of the new analytical procedure.
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| 18. |
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| 19. |
- Barrefors, Gunnar, 1963, et al.
(författare)
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Assessment by gas chromatography and gas chromatography - mass spectrometry of volatile hydrocarbons from biomass burning
- 1995
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Ingår i: Journal of Chromatography A. ; 710, s. 71-77
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Tidskriftsartikel (refereegranskat)abstract
- Well over thirty combustion-formed non-methane hydrocarbons were determined from uncontrolled burning of biogenic materials. Results are given for straw, conifer twigs, newsprint and hardwood. Samples were taken on triple-layer adsorption cartridges. After thermal desorption, the hydrocarbons were separated by gas chromatography on an aluminium oxide column. Samples were also taken with a gas syringe and analyzed after gas injection. The hydrocarbon compositions were found to be remarkably similar for different kinds of biomass. Among 21 recorded alkenes and alkadienes, ethene was predominant, and the next most prominent species were propene and 1,3-butadiene. The large proportions of ethyne and the carcinogenic benzene increased further with increasing combustion efficiency.
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| 20. |
- Barrefors, Gunnar, 1963, et al.
(författare)
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Assessment of ambient volatile hydrocarbons from tobacco smoke and from vehicle emissions
- 1993
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Ingår i: Journal of Chromatography. ; 643, s. 71-76
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Tidskriftsartikel (refereegranskat)abstract
- Quantitative proportions of C2-C8 alkenes, alkadienes, alkynes, alkanes and arenes were determined for indoor smoky air and for air inside a private car. Samples were taken on adsorbent cartridges and analysed by gas chromatography on an aluminium oxide column. The proportions of more than twenty reported alkenes, alkadienes and alkynes were demonstrated to be very similar in a smoky room and in sidestream cigarette smoke. Isoprene, ethene and propene are major components. Urban air polluted by petrol-fuelled vehicles differs mainly by having much lower proportions of isoprene and much higher proportions of petrol alkanes and alkylbenzenes. The total concentration of C2-C8 hydrocarbons was found to be similar in a smoky room and in a car in urban traffic.
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| 21. |
- Barrefors, Gunnar, 1963, et al.
(författare)
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Exposure to volatile hydrocarbons in commuter trains and diesel buses
- 1996
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Ingår i: Environmental Technology. ; 17, s. 643-647
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Tidskriftsartikel (refereegranskat)abstract
- Percentage proportions of 25 C2-C7 hydrocarbons were determined inside both diesel buses and commuter trains in regular traffic. The hydrocarbons originate predominantly from petrol-fuelled vehicles. The total proportion of unburnt petrol components (mainly alkanes and arenes) was considerably larger than the proportion of combustion-formed components (mainly ethene, ethyne and propene). The approximate relative proportions 1 :1 :0.4 :0.1 were observed for the genotoxic species benzene, ethene, propene, and 1,3-butadiene. Isoprene from expired air of the passengers constituted a prominent fraction, particularly in the buses. Samples were taken on triple-layer adsorbent cartridges and were analyzed in the laboratory by thermal desorption and gas chromatography on an aluminium oxide column. Passenger exposure to traffic-emitted volatile hydrocarbons was 2-3 times higher for diesel bus commuters than for train commuters. The presence of road vehicles nearer to the buses explains this difference. Additional pollution in buses from their diesel exhaust strengthens commuter trains as a superior alternative with respect to the exposure of the passengers to hazardous air pollutants.
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| 22. |
- Barrefors, Gunnar, 1963, et al.
(författare)
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Gas chromatographic separation of volatile furans from birchwood smoke
- 1996
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Ingår i: Journal of Chromatography A. ; 753, s. 151-155
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Tidskriftsartikel (refereegranskat)abstract
- Furan, 2-methylfuran, 3-methylfuran, 2,5-dimethylfuran and the five isomeric C6 alkylfurans, two C7 alkylfurans and three C6-C7 alkenylfurans were determined in birchwood smoke by adsorbent sampling, gas chromatography and mass spectrometric techniques. Retention data, mass spectral data and quantitative proportions are given. Furan and 2-methylfuran are major components. Contrary to other oxygen-containing compounds, the furans elute from the aluminium oxide column widely used for volatile C2-C8 hydrocarbons. The furans are formed mainly from glowing and smouldering combustion.
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| 23. |
- Barrefors, Gunnar, 1963, et al.
(författare)
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Volatile hazardous hydrocarbons in a Scandinavian urban road tunnel
- 1992
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Ingår i: Chemosphere. ; 25, s. 691-696
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Tidskriftsartikel (refereegranskat)abstract
- Vehicle-emitted hydrocarbons were assessed in the major Tingstad tunnel in Göteborg, Sweden. Samples were taken on adsorbent cartridges and analyzed by gas chromatography after thermal desorption. Although the tunnel is only 454 m long, the concentration levels were found to be approximately five times higher than inside commuter cars on roads with similar traffic.Representative proportions of non-methane hydrocarbons were 14% for alkenes, 32% for alkanes and as much as 49% for arenes. Benzene and ethene, representing particular health hazards, constituted about 7% each. Characteristic concentration ratios are given for sixteen alkenes and alkadienes.Health hazards for vulnerable motorists and implications for existing and planned road tunnels are discussed.
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| 24. |
- Barrefors, Gunnar, 1963, et al.
(författare)
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Volatile hydrocarbons from domestic wood burning
- 1995
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Ingår i: Chemosphere. ; 30, s. 1551-1556
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Tidskriftsartikel (refereegranskat)abstract
- The quantitative proportions of 16 alkenes, 5 alkadienes, 5 alkynes and several alkanes and arenes were determined in emissions from wood burning in a wood-stove and in small-scale model experiments. Samples were taken on triple-layer adsorption cartridges, and gas chromatographic separations were performed on an aluminium oxide column.Ethene, ethyne and benzene were major components, especially from efficient flame combustion. The proportions of C3-C7 alkenes were markedly higher for smouldering. The carcinogenic compounds benzene and 1,3-butadiene constituted roughly 10-20% and 1-2% by weight of total non-methane hydrocarbons. Similar results were obtained for hardwood and softwood.
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| 25. |
- Berggren, Christine
(författare)
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Affinity biosensors based on a capacitive transducer
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Capacitive biosensors were developed for several analytes such as hormones, interleukines, viruses and heavy metal ions. The sensing surfaces were prepared by immobilizing the biorecognition element to self-assembled monolayers (SAMs) on gold. SAMs form spontaneously on gold by adsorption of thiols, sulfides or disulfides. After immobilization of the biorecognition element a long chain hydrocarbon thiol was used to block any uncovered spots on the surface. The electrode was mounted in a flow-system and served as working electrode in a potentiostatically controlled system. Between measurements the working electrode was held at a rest potential of 0 mv vs. an Ag/AgCl reference electrode. To measure the capacitance at the sensing layer/electrolyte interface a potentiostatic step of 50 mV was applied and the resulting current response was recorded. By assuming that the current response followed that for a model consisting of a resistor and a capacitor in series the capacitance could be calculated by a linear least-squares fitting. Immunosensors specific for hormones and interleukines were developed with detection limits around 15 femtomolar for non-labeled antigens. DNA biosensors were developed by immobilizing a short oligonucleotide probe in two different ways; either by direct self-assembling of an SH- modified oligonucleotide or by coupling an oligonucleotide to a SAM. In both cases 0.2 attomolar of a DNA virus fragment could be detected. Also heavy metal ion specific biosensors were developed by immobilizing heavy metal specific proteins on an electrode surface by the self- assembling process. The heavy metal specific proteins are believed to change conformation when heavy metal ions bind thereby resulting in a change in capacitance. The heavy metal ions Cu2+, Zn2+, Cd2+ and Hg2+ could all be detected down to femtomolar concentrations.
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| 26. |
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| 27. |
- Beugin, S, et al.
(författare)
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New sterically stabilized vesicles based on nonionic surfactant, cholesterol, and poly(ethylene glycol)-cholesterol conjugates.
- 1998
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Ingår i: Biophysical Journal. - 0006-3495 .- 1542-0086. ; 74:6, s. 3198-3210
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Monomethoxypoly(ethylene glycol) cholesteryl carbonates (M-PEG-Chol) with polymer chain molecular weights of 1000 (M-PEG1000-Chol) and 2000 (M-PEG2000-Chol) have been newly synthesized and characterized. Their aggregation behavior in mixture with diglycerol hexadecyl ether (C(16)G(2)) and cholesterol has been examined by cryotransmission electron microscopy, high-performance gel exclusion chromatography, and quasielastic light scattering. Nonaggregated, stable, unilamellar vesicles were obtained at low polymer levels with optimal shape and size homogeneity at cholesteryl conjugate/ lipids ratios of 10 mol% M-PEG1000-Chol or 5 mol% M-PEG2000-Chol, corresponding to the theoretically predicted brush conformational state of the PEG chains. At 20 mol% M-PEG1000-Chol or 10 mol% M-PEG2000-Chol, the saturation threshold of the C(16)G(2)/cholesterol membrane in polymer is exceeded, and open disk-shaped aggregates are seen in coexistence with closed vesicles. Higher levels up to 30 mol% lead to the complete solubilization of the vesicles into disk-like structures of decreasing size with increasing PEG content. This study underlines the bivalent role of M-PEG-Chol derivatives: while behaving as solubilizing surfactants, they provide an efficient steric barrier, preventing the vesicles from aggregation and fusion over a period of at least 2 weeks.
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| 28. |
- Bjarnason, Bjarni
(författare)
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Use of Biorecognition Elements or Their Mimics in New Flow Analysis Systems
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- We have evaluated capacitive and thermal transducers for recognition of bio- molecular interactions with different analytes. These assays were made in flow analysis systems because of the simplicity such methods provide. A capacitive transducer, based on a surface modified gold electrode, has the ability to monitor affinity based interactions directly, provided that the interactions introduce measurable changes in the dielectric layer on the surface of the electrode. The method is capable of very low detection limits for various analytes. Interleukin 6 has, for example, been detected down to femtomolar concentrations . For the determination of urea in serum we have applied a thermal transducer fitted in a flow cell. The enzyme urease was used to selectively hydrolyze urea in an injected serum sample. In the hydrolysis process, heat is produced that can be used for quantifying urea in serum. The approach applied here was heat conduction calorimetry where a reactor has been placed on the surface of a thermocouple plate (TC-plate). This approach allowed detection of urea in serum in the range of 0.5-10 mM. One of the greatest advantages of the method is the insensitivity of the sensor towards changes in the flow rate. The method does thus not require careful optimization of the flow rate. Changes in flow rate during analysis are also not expected to influence the quality of the results. This was also reflected in the low standard deviation (< 2%) of repeatedly injected samples. Immunoassays for pesticide determinations have also been evaluated in this work. The common way of conducting an immunoassay is by the use of ELISA plates. Efforts have been made, however, to simplify the assay procedure by applying flow injection techniques. This will simplify the automation protocol for such assays as well as reduce analysis time per sample. The difference between the various flow injection immuno analysis formats is often how the free un-reacted tracer is separated from the tracer-antibody complex. Results have shown that immobilization of the antibody may not always be the most suitable method of analysis because of the hostile environment the regeneration solution provides for the antibody. Therefore immobilization of antibody receptors like protein-A or G have been considered. The regeneration of the protein instead of the antibody appearers to be a suitable solution to the problem. We have furthermore applied molecular imprinted polymers for selective, on-line, extraction of triazines from contaminated water samples, which allowed simultaneous determination of low concentrations (at least 0.5 ng/ml) of several triazines in solutions containing 20 ppm humic acid.
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| 29. |
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| 30. |
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| 31. |
- Björklund, Erland
(författare)
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Determination of Persistent Organic Pollutants in Solid Environmental Samples Using Accelerated Solvent Extraction and Supercritical Fluid Extraction. Exhaustive extraction and sorption/desorption studies of PCBs.
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Human activity is constantly causing environmental problems due to production and release of numerous chemicals. A group of compounds of special concern is persistent organic pollutants (POP). These toxic, lipophilic chemicals have a high chemical and biological stability, and tend to accumulate in the lipid phase of living organisms. A major sink for POPs are sediments, and consequently these are important for the distribution of POPs in the aquatic environment. Traditionally, determination of POPs relay on exhaustive extraction using liquid extraction techniques (e.g. Soxhlet extraction developed in the late 19th century) followed by gas chromatographic analysis. Since liquid-solid extraction normally requires large volumes of organic solvents in combination with long extraction times and extract clean-up, there has been an increasing demand for improved technology. This should result in reduced organic solvent consumption and sample preparation time, at the same time improving the environment and cutting costs for POP monitoring. In this thesis two modern techniques with capability of fulfilling at least one of these goals have been investigated: (1) Supercritical Fluid Extraction (SFE), and (2) Accelerated Solvent Extraction (ASE). Polychlorinated biphenyls (PCBs) were chosen as model compounds in all experiments performed on environmental matrices, since they cover a relatively large range of physiochemical parameters. Important parameters influencing the overall extraction efficiency in ASE and SFE, are discussed and illustrated for a large number of sediments. It was demonstrated that, by careful consideration of the experimental parameters, both techniques are capable of replacing old methods such as Soxhlet extraction. ASE is somewhat faster than SFE, but the extracts generated in SFE are much cleaner and can be analyzed without sample clean-up. Consequently the overall sample preparation time may be substantially lower using SFE. However, ASE is important to verify that the developed SFE methods are exhaustive. It is quite clear though that there is no reason to continue using for example Soxhlet extraction, which should be replaced in routine laboratories. The possibility of utilizing SFE as a selective tool in sorption/desorption studies of POPs in natural sediments was also addressed. This second objective was proven successful and sediments could be characterized in terms of resistance towards desorption of bound analytes under supercritical conditions. These data could be correlated to desorption processes occurring under natural conditions. Additionally it could be verified that sorption of POPs from water to sediment is a very slow process requiring months or even years. This supports recent research results, demonstrating that distribution coefficients many times are underestimated since the system has not reached equilibrium.
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| 32. |
- Björkqvist, Susan, 1967, et al.
(författare)
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Isoprene from expired air inside a private car
- 1997
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Ingår i: The science of the total environment. ; 207, s. 63-67
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Tidskriftsartikel (refereegranskat)abstract
- The concentration of isoprene inside a small-sized parked private car with one person was found to be of the order of 20 g/m3. Isoprene was then the major non-methane volatile hydrocarbon except in strongly traffic-polluted parking places. On driving, with intermediate fan ventilation, the isoprene levels were one order of magnitude lower. In the empty car, the concentrations were still much lower, proving that isoprene originates predominantly from expired air. Air samples were taken on triple-layer adsorbent cartridges and were analysed for volatile hydrocarbons by gas chromatography after thermal desorption. The analytical aluminium oxide column permitted simultaneous determination of a range of reported traffic-emitted hydrocarbons including the carcinogenic 1,3-butadiene and benzene.
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| 33. |
- Björkqvist, Susan, 1967
(författare)
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Source-specific volatile organic compounds in human breath, wood smoke and biogas
- 1997
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Volatile biogenic compounds are often overlooked in air quality studies. This work deals with the analysis of specific organic compounds of biogenic origin and with their sources. General aspects of indoor air chemistry and measurements of volatile organic compounds in indoor air are also discussed. The determinations were based mainly on adsorbent sampling followed by gas chromatographic separations on different types of suitable columns. Identifications were made by mass spectrometry.
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| 34. |
- Borén, Kristina, et al.
(författare)
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Rapid ion-exchange chromatography for preparative separation of proteins IV. Application to bovine carbonic anhydrase III from skeletal muscle
- 1991
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Ingår i: Journal of Chromatography A. - : Elsevier BV. - 0021-9673 .- 1873-3778. ; 588:1-2, s. 139-145
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Tidskriftsartikel (refereegranskat)abstract
- Bovine muscle carbonic anhydrase III was purified to homogeneity by the strategy of rapid ion-exchange chromatography. The ionic exchanger used was CM-cellulose, and this is the first application of this technique on a cation exchanger. Nitrogen gas was used to pressurize the chromatographic column to accelerate the elution. The results show that proteins with high isoelectric points can also be purified in this way. The procedure is very time-saving compared with conventional chromatography, reducing the elution time five-to ten-fold. The proteins are in addition protected against oxidation by air.
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| 35. |
- Burestedt, Elisabeth
(författare)
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Enzymatic and Immunological Detection Principles for Environmental and Biological Applications
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of the thesis was to develop new analytical detection principles based on enzymatic and immunological reactions for sensitive, selective, cost-effective and high sample through-put detection devices. The thesis presents the basic elements and reaction paths necessary for the construction and development of enzyme based amperometric biosensors and immunoassays. The developed biochemical detection devices were utilised for the analysis of phenolic compounds, s-triazine herbicides, D-amino acids and interleukin-8. The thesis thus covers applications in both environmental and biological samples. D-amino acid biosensors were developed by co-immobilising D-amino acid oxidase and peroxidase into carbon paste electrodes. The detection principle is based on coupled reactions between the two enzymes. Various types of tyrosinase amperometric biosensors were developed for the analysis of mono- and di-phenolic compounds. An amplification of the overall signal is possible to achieve by the reduction of the enzymatically produced product at the electrode surface. Amplification factors and rate limiting steps of three different sensor configurations were investigated in order to further improve the sensitivity and stability of tyrosinase based amperometric biosensors. The developed tyrosinase biosensors were integrated on-line with sample handling and liquid chromatographic techniques for the analysis of phenolic compound in environmental as well as biological samples. An enzyme flow immunoassay technique for atrazine using b-galactosidase as the enzyme label and a cellobiose dehydrogenase (CDH) biosensor as the label detector was developed. The optimised system was applied to the analysis of atrazine in spiked surface water samples, by utilising both the CDH biosensor and colourimetric detection. A non-competitive flow immunoassay method was developed for the analysis of interleukin-8 in cell samples.
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| 36. |
- Burestedt, E., et al.
(författare)
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Optimisation and validation of an automated solid phase extraction technique coupled on-line to enzyme-based biosensor detection for the determination of phenolic compounds in surface water samples
- 1995
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Ingår i: Chromatographia. - Heidelberg : Springer Berlin/Heidelberg. - 0009-5893 .- 1612-1112. ; 41:3-4, s. 207-215
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Tidskriftsartikel (refereegranskat)abstract
- A fully integrated screening system for phenolic compounds was developed incorporating on-line solid phase extraction, fractionation and biosensor detection. Two different types of biosensors, solid graphite and carbon paste electrodes incorporating the enzyme tyrosinase, were compared and used in the screening system. Interfacing of the solid phase extraction and fractionation with the biosensor detection was given special attention since the biosensors were not compatible with the organic modifier used for desorption of phenols from the solid phase extraction step. The system was validated with conventional analytical techniques. Surface water samples from the Ebro river were spiked with 1,10, and 25μg L−1 of catechol, phenol,p-cresol, respectively. Three out of seven samples were spiked and the correct samples were identified, containing phenols equivalent to the spiked concentrations. © 1995 Friedr. Vieweg & Sohn Verlagsgesellschaft mbH.
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| 37. |
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| 38. |
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| 39. |
- Danielsson, Bengt, et al.
(författare)
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Heat Sensitive Biosensors
- 1993
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Ingår i: Uses of Immobilized Biological Compounds. - Dordrecht : Springer Netherlands. - 0168-132X. - 9780792325291 - 9789401048545 - 9789401119320 ; 252, s. 541-548
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Bokkapitel (refereegranskat)abstract
- The unsurpassed versatility of heat sensitive biosensors is illustrated by various new applications of the flow-calorimetric biosensor system, the enzyme thermistor (ET) developed in our laboratory. The ET measures the reaction heat in a small column containing immobilized biocatalyst. Since most biological reactions are exothermic, the ET has a very broad applicability and numerous assays of clinical as well as biotechnological interest have been studied. The procedure is well suited for monitoring and control of biotechnological processes due to its high operational stability. New results from this area are presented as well as developments on an automated thermometric immunoassay (TELISA). Miniaturized ET-devices are suitable for portable monitoring of, for instance, blood glucose. Other recent work include determinations in organic solvents, direct characterization of immobilized biocatalysts, and monitoring of bioactivities in solution.
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| 40. |
- Danielsson, B., et al.
(författare)
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Recent investigations on calorimetric biosensors
- 1992
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Ingår i: Sensors and Actuators B: Chemical. - 0925-4005. ; 6:1-3, s. 138-142
-
Tidskriftsartikel (refereegranskat)abstract
- New applications of a flow-calorimetric biosensor system, the enzyme thermistor (ET) are described. The ET measures the reaction heat in a small column containing immobilized biocatalyst as a temperature change of the effluent from the column. Since most biological reactions are exothermic, the ET has a very broad applicability and numerous assays of clinical as well as biotechnological interest have been studied. The procedure is well suited for monitoring and control of biotechnological processes due to its high operational stability. New results from this area are presented as well as developments on an automated thermometric immunoassay (TELISA). Miniaturized ET devices are suitable for portable monitoring of, for instance, blood glucose. Other recent work includes determinations in organic solvents, direct characterization of immobilized biocatalysts and monitoring of bioactivities in solution.
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| 41. |
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| 42. |
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| 43. |
- Demirbüker, Mustafa
(författare)
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Analysis of lipids by supercritical fluid chromatography
- 1992
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis is described the development of new metods for the analysis of triacylglycerols and fatty acid methyl esters by supercritical fluid chromatography. Packed micro columns have been utilized for SFC and the properties of different types of packing materials have been evaluated. For evaluation, columns were thus in situ impregnated with silver ions (argentation), permanganate, periodate and triazine-based dyes. Columns packed with silica particles have also been investigated. With all these phases, it appears that the silica surface residual silanols were deactivated with regard to interaction with solute molecules when small amounts of modifiers were added to the mobile phase. For elution of unsaturated compounds on silver impregnated columns, it was necessary to add a higher content of modifiers to the mobile phase in order to achieve a partial deactivation of the double bond/silver ion complexes. It was not possible to use a flame ionization detector with such mobile phases. Therefore an ultraviolet ( UV ) detector must be utilized for the detection, even though the responses for triacylglycerols and fatty acid methyl esters were strongly dependent on the number of double bonds. Excellent separations of triacylglycerols and of fatty acid methyl esters have been obtained. Further, the columns were extremely stable from a physical as well as from a chemical point of view.For quantitative analysis of saturated and unsaturated triacylglycerols a miniaturized evaporative light scattering detector ( ELSD ) for connection to packed micro columns SFC has been developed. This detector could be used with pressure programming and the detection limit was lower than 6 ng.
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| 44. |
- Dérand, Helene, et al.
(författare)
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Pol(ethylene glycol) Graft Copolymers Containing Carboxylic Acid Groups: Aggregation and Viscometric Properties in Aqueous Solution
- 1996
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Ingår i: Macromolecules. - 0024-9297. ; 29:27, s. 8770-8775
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Tidskriftsartikel (refereegranskat)abstract
- Poly(ethylene glycol) monomethyl ethers (MPEG) were grafted on copolymers of maleic anhydride and styrene, methyl methacrylate, and ethylhexyl methacrylate, respectively. Hydrolysis of the remaining anhydride residues gave graft copolymers carrying a large number of carboxylic acid groups along the main chains. The properties in aqueous solutions of these graft copolymers were studied with respect to aggregation behavior and viscometric properties, Aggregation of the polymers was examined by quasi-elastic light scattering and now field-flow fractionation in water and KCl solution. Both methods showed that the anionic graft copolymers mainly were present as single molecules in pure water, with a minor fraction of aggregates. In KCI solution, aggregates with average sizes of approximately 30 nm were the dominant species. In aqueous solution, the polymers exhibited polyelectrolyte behavior, i.e., a dramatic increase of the viscosity upon neutralization. Graft copolymers with hydrophobic groups in the backbone had lower viscosities.
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| 45. |
- Djane, N K, et al.
(författare)
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Chromium speciation in natural waters using serially connected supported liquid membranes.
- 1999
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Ingår i: Talanta. - 1873-3573. ; 48:5, s. 1121-1132
-
Tidskriftsartikel (refereegranskat)abstract
- A supported liquid membrane (SLM) method for the speciation of chromium has been developed. The method is based on selective extraction and enrichment of anionic Cr(VI) and cationic Cr(III) species in two serially connected SLM units. Methyltricaprylammonium chloride (Aliquat) and di-(2-ethylhexyl) phosphoric acid (DEHPA), respectively were used as the selective extractants in the membrane liquid. Graphite furnace atomic absorption spectrometry (GFAAS) was utilised for final determination. Optimised conditions for the DEHPA membrane were, sample solution at pH 3, acceptor solution 0.1 M HNO(3) and 10% w/w carrier in kerosene. The corresponding values for the Aliquat membrane were pH 7, 0.75 M HNO(3) and 6% w/w carrier in di-n-hexylether. This gave extraction efficiencies for Cr(III) and Cr(VI) of 90 and 40%, respectively. The method was used to measure the concentration of Cr III and Cr VI in surface water from an abandoned tannery site. Storage experiments at different pH showed that preservation at neutral pH gave almost constant values over a period of one month. At acidic pH (pH=3.0) the concentration of Cr(VI) decreased rapidly while the concentration of Cr(III) increased. The detection limit, expressed as three times the standard deviation of enriched blank samples was 0.01 mug l(-1).
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| 46. |
- Dzgoev, Anatoli, et al.
(författare)
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Microformat Imaging ELISA for Pesticide Determination
- 1996
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 1520-6882 .- 0003-2700. ; 68:19, s. 3364-3369
-
Tidskriftsartikel (refereegranskat)abstract
- A flat-well microformat competitive enzyme-linked immunosorbent chemiluminescent assay for the detection of the pesticide 2,4-dichlorophenoxyacetic acid (2,4-D) is described. Thick-film technology was used to pattern a hydrophobic layer 100 μm thick onto glass microscope slides to form an array of 2 × 2 mm2 squares. These flat wells were able to hold 2 μL of reagents, corresponding to a height of ∼500 μm, with minimal contamination risk. The hydrophobic ink used to pattern the surfaces allowed significantly larger volumes of samples to be applied when compared with surfaces patterned with nonhydrophobic inks. This reduced evaporation effects and permitted greater pipetting accuracy, thereby improving assay reproducibility. A competitive immunoassay was developed based on the ability of free 2,4-D hapten to inhibit binding of anti-2,4-D monoclonal antibodies to 2,4-D−bovine serum albumin conjugate adsorbed onto the glass support. The support was subsequently incubated with alkaline phosphatase (AP) labeled anti-mouse IgG. The amount of AP conjugate bound was determined by quantitating the chemiluminescent emission produced from the enzymatic breakdown of CSPD substrate by AP using a cooled CCD camera. The detection limit of the single-sample microformat assay was 2.7 × 10-11 M, or 6 pg of 2,4-D. The linear ranges of the single-sample and multisample assays were 4.5 × 10-8−4.5 × 10-11 and 4.5 × 10-7−1.66 × 10-10 M, respectively. In comparison, the detection limits of a tube-based chemiluminescent assay using standard luminometer and of a colorimetric ELISA were 45 × 10-11 and 9.9 × 10-8 M, respectively. The ability to scale the thick-film-based microformat assay makes it an ideal candidate for the development of affinity arrays and high-throughput assay formats. Prospects for further improvements of this imaging ELISA strategy will be discussed.
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| 47. |
- Ekedahl, Lars-Gunnar, et al.
(författare)
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Hydrogen sensing mechanisms of metal insulator interfaces
- 1998
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Ingår i: Accounts of Chemical Research. - 0001-4842 .- 1520-4898. ; 31:5, s. 249-256
-
Tidskriftsartikel (refereegranskat)abstract
- The hydrogen sensitivity of palladium-silicon dioxidesilicon (Pd-MOS) structures was demonstrated about 25 years ago. One of the most interesting features of the Pd-MOS device as a hydrogen sensor is its very large dynamic pressure range. Such devices are now used in several practical applications and in commercially available equipment, both as single sensors and in sensor arrays. We recall that the hydrogen sensitivity of the device occurs due to a hydrogen induced polarization at the Pd-SiO2 interface as schematically shown in Figure 1. During the years, several types of devices have been developed, both with insulators other than silicon dioxide and catalytic metals other than palladium. Furthermore, it has been demonstrated that sensors with thin, discontinuous catalytic metals can detect molecules, like ammonia, which are not detected by sensors with thick continuous palladium gates. 1-3 Although several insulators have been used in hydrogen sensitive Pd-insulator-semiconductor
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| 48. |
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| 49. |
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| 50. |
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