| 1. |
- Adeyemi, David, et al.
(författare)
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Electrospun Nanofibers Sorbents for Pre-Concentration of 1,1-dichloro-2,2 bis-(4-chlorophenyl)ethylene with Subsequent Desorption by Pressurized Hot Water Extraction
- 2011
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Ingår i: Chromatographia. - : Springer Science and Business Media LLC. - 0009-5893 .- 1612-1112. ; 73:9-10, s. 1015-1020
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Tidskriftsartikel (refereegranskat)abstract
- Electrospun polystyrene (PS) nanofibers (130-500 nm) incorporating a potassium salt of imidazole-1-carbodithioate were evaluated as potential sorbents for the pre-concentration of a model organochlorine pesticide; 1,1-dichloro-2,2bis-(4-chlorophenyl)ethylene (DDE). The efficiencies of DDE (0.25-1.0 mu g L-1) adsorption by the nanofiber sorbent followed by desorption employing pressurized hot water extraction (PHWE) were investigated and monitored using gas chromatography with electron capture detection (GC-ECD). Parameters such as time, temperature and pressure of extraction, sample volume, DDE concentration and sorbent mass were optimized. The maximum adsorption of DDE (0.50 mu g L-1) on electrospun PS and carbodithioate incorporated PS nanofibers was at 43.7 and 94.6%, respectively, in 20 min. Incorporation of carbodithiote doubled the adsorption efficiency of PS and achieved LOD of 0.000234 mu g L-1 for DDE. The optimal DDE desorption on the PHWE system was 93.8% in 10 min. It would seem that the use of electrospun nanofibers as sorbent material with subsequent desorption by PHWE has great potential and thus warrants further investigations. This approach as it uses water as an extraction solvent for an organochlorine pesticide provides an opportunity to eliminate organic solvents, especially for procedures aimed at monitoring organic pollutants in the environment.
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| 2. |
- Batlokwa, Bareki Shima, et al.
(författare)
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A Novel Molecularly Imprinted Polymer for the Selective Removal of Chlorophyll from Heavily Pigmented Green Plant Extracts prior to Instrumental Analysis
- 2013
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Ingår i: Journal of Chemistry. - : Hindawi Limited. - 2090-9071 .- 2090-9063.
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Tidskriftsartikel (refereegranskat)abstract
- A novel molecularly imprinted polymer (MIP) powder designed for the selective removal of interfering chlorophyll pigment from heavily pigmented green plant extracts during pesticide residue analysis or analysis for bioactives in natural product research is reported. The polymer powder imprinted with chlorophyll.. was synthesized by copolymerizing the functional and cross-linking monomers, methacrylic acid (MAA) and ethylene glycol dimethacrylate (EGDMA), respectively. During batch rebinding experiments, the MIP effectively removed chlorophyll from neat chlorophyll standards, green medicinal plants, and spinach extracts with determined absorbance as high as 2.501 absorbance units (Au) to as low as 0.084 Au after the optimum quantity of the MIP (170 mg mL(-1)) was added as the adsorbent prior to instrumental analysis. The determined 0.084 Au absorbance was far below the absorbance of 2% chlorophyll (0.401 Au) regarded as the cut-off point for interfering chlorophyll. Thus the newly developed polymer presents itself as a suitable adsorbent for the selective removal of chlorophyll from heavily pigmented, chlorophyll containing extracts.
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| 3. |
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| 4. |
- Karlsson, Eva Nordberg, et al.
(författare)
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Enzymatic specificity and hydrolysis pattern of the catalytic domain of the xylanase Xyn1 from Rhodothermus marinus
- 1998
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Ingår i: Journal of Biotechnology. - 0168-1656. ; 60:1-2, s. 23-25
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Tidskriftsartikel (refereegranskat)abstract
- The catalytic domain of a xylanase from Rhodothermus marinus was produced in Escherichia coli. The catalytic domain belongs to glycosyl hydrolase family 10. The produced protein has a 22-amino acid leader peptide followed by a 411-amino acid truncated xylanase. The molecular mass was 48 kDa and the recombinant xylanase had a pI of 4.9. The pH and temperature optima for activity were determined to be 7.5 and 80°C, respectively. At that temperature the enzyme had a half-life of 1 h 40 min. An addition of 1 mM calcium stabilized the activity of the enzyme at 80°C. The xylanase had its highest specific activity on oat spelt xylan but was active also on other xylans and to a limited extent on some other polysaccharides (soluble glucans). No exo- or endo-cellulase activity was observed. Hydrolysis of xylo-oligomers and oat spelt xylan was studied and the predominant products of hydrolysis were xylobiose and xylotriose. The enzyme was inactive on xylobiose, xylotriose and on the soluble fraction from oat spelt xylan. The R. marinus xylanase is shown to have a strong preference for internal linkages and is therefore classified as an endo-xylanase. Copyright (C) 1998 Elsevier Science B.V.
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| 5. |
- Patil, Sunil, et al.
(författare)
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Electrospun carbon nanofibers from polyacrylonitrile blended with activated or graphitized carbonaceous materials for improving anodic bioelectrocatalysis.
- 2013
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Ingår i: Bioresource Technology. - : Elsevier BV. - 1873-2976 .- 0960-8524. ; 132, s. 121-126
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Tidskriftsartikel (refereegranskat)abstract
- The electrospun carbon nanofibers obtained from polyacrylonitrile (PAN) and PAN blends with either activated carbon (PAN-AC) or graphite (PAN-GR) were tested as anodes using Shewanella oneidensis MR-1. Extensive physico-chemical and electrochemical characterization confirmed their formation, their fibrous and porous nature, and their suitability as electrodes. N(2) adsorption measurements revealed high specific surface area (229.8, 415.8 and 485.2m(2) g(-1)) and porosity (0.142, 0.202 and 0.239cm(3)g(-1)) for PAN, PAN-AC and PAN-GR, respectively. The chronoamperometric measurements showed a considerable decrease in start-up time and more than a 10-fold increase in the generation of current with these electrodes (115, 139 and 155μAcm(-2) for PAN, PAN-AC and PAN-GR, respectively) compared to the graphite electrode (11.5μAcm(-2)). These results indicate that the bioelectrocatalysis benefits from the blending of PAN with activated or graphitized carbonaceous materials, presumably due to the increased specific surface area, total pore volume and modification of the carbon microstructure.
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| 6. |
- Torto, Nelson
(författare)
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Microdialysis Sampling, Electrochemical Detection and Mass Spectrometry of Carbohydrates in Monitoring Bioprocesses
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis addresses; (1) the microdialysis experiment, application and methodology to maximise its performance when sampling from enzymatic bioprocesses, (2) electrochemical detection and electrochemical oxidation of carbohydrates on Au as well as Cu electrodes in alkaline solutions, and (3) coupling and maximising the performance of a microdialysis sampling based high performance anion exchange chromatography-integrated pulsed electrochemical detection-mass spectrometry system. Studies were carried out to investigate the effect of temperature, analyte as well as biomatrix complexity, analyte concentration, permeability factors, protein(enzyme)-membrane interaction and membrane material on the performance of microdialysis sampling. The performance data, as indicated by the extraction fraction, was correlated with membrane characteristics as reflected by their SEM micrographs in the dehydrated state. The performance of the membranes appeared not to be significantly affected by continuously sampling at 90°C, for up to 24 h. All membranes showed some degree of interaction with enzymes (and biomatrix), and the subsequent decrease in performance was associated with the so-called Andrade effect. A method for the in-situ modification of microdialysis membranes by surface coating with PEI, in view to coimmobilise PEI-PEG so as to suppress membrane-protein interaction was developed. Microdialysis sampling, continuous flow as well stopped flow modes were employed for sampling during the characterisation of hydrolytic properties of enzymes and enzyme substrates. The IPED monomer and molar unit sensitivity was investigated for manno- and maltooligasaccharides. As the results indicated to a homologous series dependent response, electrochemical oxidation studies were carried out on fresh as well as modified Cu RDE in order to evaluate n and k values, and compare these to those obtained for Au. Electrochemical oxidation mechanism for monosaccharides on Cu, was found to be different from that reported on Au. The oxidation of hexoses proceeded with a passage of 12 electrons, but that of disaccharides, appeared to be oxide dependent as 2-18 electrons were observed. MS was used for the qualitative evaluation of saccharides during the enzymatic hydrolysis of wheat starch. A membrane desalting device, employing water as the regenerant was used to desalt up to 600 mM Na+ from the chromatographic effluent.
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| 7. |
- Torto, Nelson, et al.
(författare)
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On-line quantitation of enzymatic mannan hydrolysates in small-volume bioreactors by microdialysis sampling and column liquid chromatography-integrated pulsed electrochemical detection
- 1996
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Ingår i: Journal of Chromatography A. - : Elsevier BV. - 0021-9673. ; 725:1, s. 165-175
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Tidskriftsartikel (refereegranskat)abstract
- Quantitative aspects of on-line microdialysis sampling are investigated with respect to sampling in small-volume bioreactors. Three modes of microdialysis sampling; continuous-flow microdialysis sampling (CFMS), stopped-flow microdialysis sampling with continuous stirring, and stopped-flow microdialysis sampling with stopped stirring were investigated as a possible means for studying bioprocesses. The hydrolytic properties of a well characterised endomannanase from Aspergillus niger were studied using 0.01% ivory nut mannan as substrate in a 5-ml reaction vessel. On-line sampling was achieved using a microdialysis probe fitted with an SPS 6005 membrane. Stopped-flow microdialysis sampling was found to give the least analyte depletion and thus used for quantitation of the enzymatic hydrolysates. However, CFMS can be used when analyte depletion is not significant (large-volume reactor). Hydrolysis of ivory nut mannan gave mainly mannobiose and mannotriose in almost equal amounts, which is consistent with an endo-wise hydrolysis. The concentrations of mannose and mannopentaose did not change significantly over the monitoring period, however, that of mannotetraose increased gradually up to 11 h where it starts to decrease.
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