| 1. |
- Dzgoev, A., et al.
(författare)
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Optimization of a charge coupled device imaging enzyme linked immuno sorbent assay and supports for the simultaneous determination of multiple 2,4-D samples
- 1997
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Ingår i: Analytica Chimica Acta. - 0003-2670. ; 347:1-2, s. 87-93
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Tidskriftsartikel (refereegranskat)abstract
- A chemiluminescent microformat enzyme linked immune sorbent assay (ELISA) has been optimized for the simultaneous determination of multiple 2,4-dichlorophenoxyacetic acid (2,4-D) samples. The competitive immunoassay employed a 2,4-D-BSA conjugate, anti-2,4-D monoclonal antibodies and alkaline phosphatase (AP) labelled anti-mouse IgG. The bound AP conjugate was determined by quantitating the chemiluminescence emission from the enzymatic decomposition of the luminogenic substrate, CSPD, by AP using a cooled charge coupled device (CCD) camera. The detection limit for the simultaneous determination of multiple samples was 4.3x10-10 M corresponding to 96 pg ml-1 or 192 fg well with a coefficient of variation (CV, %) of 12.5%. The linear range of the assay was 4.5 x 10-7-4.5 x 10-10 M. The ability of gold coated silicon wafers and glass capillaries to serve as solid phase supports in the imaging ELISA was investigated. The highly reflective gold surfaces improved both the linear range and the sensitivity of the assay, as compared to thick-film patterned surfaces. The capillary supports, on the other hand, lead to a reduction in the linear range and the sensitivity of the assay, as compared to the thick-film patterned surfaces. Initial studies indicate that the capillaries guide the light and may provide a built-in mechanism for collecting the emitted light. Strategies for further development of support materials for imaging-based detectors will be discussed.
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| 2. |
- Gascón, Jordi, et al.
(författare)
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Performance of two immunoassays for the determination of atrazine in sea water samples as compared with on-line solid phase extraction-liquid chromatography-diode array detection
- 1996
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Ingår i: Analytica Chimica Acta. - : Elsevier BV. - 0003-2670. ; 330:1, s. 41-51
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Tidskriftsartikel (refereegranskat)abstract
- Two immunoassay formats, magnetic particles-based assay (Atrazine RaPID assay and Atrazine High-Sensitivity RaPID assay) and microtiter plate based assay (Department of Entomology and Environmental Toxicology, University of California in Davis) were evaluated for the determination of atrazine in sea water samples. The results obtained were compared and validated with those obtained by using on-line solid phase extraction followed by liquid chromatography-diode array detection (on-line SPE-LC-DAD). The correlation between both techniques was good when analyzing levels of atrazine ranging from 0.01 to 5 μg/l in samples showing salt concentration values varying from 0 to 35 g/l and pH values from 2 to 10. One of these immunoassays (Atrazine High-Sensitivity RaPID assay) was employed to directly analyze atrazine in real estuarine and coastal water samples. The same samples were analyzed after filtration and C18 Empore disks extraction.
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| 3. |
- Hedenfalk, M., et al.
(författare)
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Modulation of the measuring range of a radioimmunoassay using an organic water two phase system
- 1997
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Ingår i: Analytica Chimica Acta. - 0003-2670. ; 341:2-3, s. 269-274
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Tidskriftsartikel (refereegranskat)abstract
- A commercially available radioimmunoassay (RIA) kit was used to study the effects of organic solvents on antigen-antibody interactions. The RIA analysis was carried out in aqueous-organic two phase systems. After exposure to hydrophobic organic solvents the antibodies retained full binding capacity, while less hydrophobic solvents caused partial inactivation of the antibodies. A practical analysis for digoxigenin in organic solvents was developed using the RIA kit with polyclonal antibodies against digoxin. The sensitivity was modulated four orders of magnitude by the choice of organic solvent. The main factor influencing the sensitivity was the partitioning of digoxigenin between the aqueous and the organic phases. The technique developed is promising for the analysis of a variety of antigens dissolved in organic solvents.
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| 4. |
- Momeni, Naghi, et al.
(författare)
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CCD-camera based capillary chemiluminescent detection of retinol binding protein
- 1999
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Ingår i: Analytica Chimica Acta. - 0003-2670. ; 387:1, s. 21-27
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Tidskriftsartikel (refereegranskat)abstract
- A chemiluminescence (CL) assay for retinol-binding protein (RBP) was designed and optimized using a charge coupled device (CCD)-camera based detection system. A sandwich ELISA was designed based on the anti-RBP antibodies immobilized in glass capillaries pre-treated with silica sol. The immobilization was predominantly by physisorption of the protein on the silica surface. The RBP bound to the anti-RBP antibodies was detected by using an anti-RBP-horseradish peroxidase (HRP) conjugate. The reaction of the HRP with hydrogen peroxide and luminol and 4-iodophenol generated the CL. The CL emitted from the glass capillaries was detected by a cooled slow scan CCD camera at an optimized exposure time. The approximately linear range of RBP determination was between 11 pg ml−1 and 11 ng ml−1 with a coefficient of variation of 5–11% (n=6) over this range.
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| 5. |
- Tang, Xiao-Jing, et al.
(författare)
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Polyethyleneimine-coated reticulated vitreous carbon electrode with immobilized enzymes as a substrate detector
- 1998
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Ingår i: Analytica Chimica Acta. - 0003-2670. ; 374:2-3, s. 185-190
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Tidskriftsartikel (refereegranskat)abstract
- Polyethyleneimine (PEI) was covalently coupled to carbodiimide-activated reticulated vitreous carbon (RVC). The PEI-coated RVC was activated with glutaraldehyde, and glycerol dehydrogenase and diaphorase were then immobilized. The PEI-coated RVC with immobilized enzymes functioned both as an enzyme reactor and a working electrode in an amperometric detection system where NAD+/NADH was recycled by the immobilized enzymes. The coated RVC electrode showed good properties compared to uncoated RVC, such as a long lifetime and a constant response to a series of injections in a flow-injection system, resulting in a relative standard deviation of 1.4%. The calibration graph was linear from the detection limit 0.1μM to 2mM NADH in the absence of recycling.
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| 6. |
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| 7. |
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| 8. |
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| 9. |
- Jonsson, Tobias, et al.
(författare)
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Heterocyclic compounds as catalysts in the peroxyoxalate chemiluminescence reaction of bis(2,4,6-trichlorophenyl)oxalate
- 1998
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Ingår i: Analytica Chimica Acta. - Amsterdam : Elsevier. - 0003-2670 .- 1873-4324. ; 361:3, s. 205-215
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Tidskriftsartikel (refereegranskat)abstract
- Substituted imidazoles and leaving groups known from other areas of chemistry have been tested for catalytic efficiency in the peroxyoxalate chemiluminescence (PO-CL) reaction, using bis(2,4,6-trichlorophenyl)oxalate (TCPO) as reagent. Catalytic activity was found for 1,2,4-triazole, 1-methylimidazole, 2-methylimidazole, 4-methylimidazole and 4,5-dichloroimidazole, while 2-mercaptoimidazole, 2-nitroimidazole, 4-nitroimidazole, benzimidazole, benzotriazole, thiazole, o-benzoic sulfimide, phthalimide, succinimide, 2(1H)-pyridone and 1,2,3-benzotriazine-4(3H)-one yielded no detectable chemiluminescence under the conditions used. None of the tested compounds was more efficient than imidazole in catalyzing the PO-CL reaction. Spectrophotometric measurements of the catalytic breakdown of TCPO showed that an intermediate was formed with almost all catalysts, and that intermediates that were more stable or present at lower concentration led to a reduced catalytic efficiency in the PO-CL reaction of TCPO.
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| 10. |
- Jonsson, Tobias, et al.
(författare)
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Very fast peroxyoxalate chemiluminescence
- 1999
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Ingår i: Analytica Chimica Acta. - Amsterdam : Elsevier. - 0003-2670 .- 1873-4324. ; 400:1-3, s. 257-264
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Tidskriftsartikel (refereegranskat)abstract
- Peroxyoxalate chemiluminescence (PO-CL) detection offers an advantage in chromatographic detection, by the virtue of its multiple unique selectivities and high sensitivity. However, many of the analytical separation techniques available today require observation times in the millisecond range to preserve the band resolution, and as the reaction kinetics of the PO-CL reaction is considerably slower, extra flow elements are needed to observe the reaction in a time window at maximum emission intensity. Since these flow elements increase the complexity of the system and contribute to band-broadening, the rational way to adapt PO-CL detection to miniaturised separation systems is to speed up the reaction, so that it emits an initial burst of light within the acceptable detection time-frame. Although this may result in a lower overall quantum yield, the actual detection sensitivity could be equal to, or better than slower PO-CL systems. By making careful selections of oxalic reagent and catalyst(s) the reaction can be fine-tuned to maximise the intensity. In this work, the time-dependent light emission from the reaction of bis(2,4,6-trichlorophenyl)oxalate (TCPO) was studied under the catalytic influence of imidazole, 1,2,4-triazole, 4-dimethylaminopyridine (DMAP), and 1,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU) in acetonitrile. Both DMAP and DBU accelerated the reaction substantially, but the best combination of reaction speed and intensity was found for a mixture of 0.5 mM DBU and 5 mM 1,2,4-triazole, which reached its maximum emission after only 40 ms and had an emission intensity comparable to that seen with 5 mM imidazole as catalyst.
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| 11. |
- Larsson, Ted, et al.
(författare)
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Electron transfer between cellobiose dehydrogenase and graphite electrodes
- 1996
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Ingår i: Analytica Chimica Acta. - : Elsevier. - 0003-2670 .- 1873-4324. ; 331:3, s. 207-215
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Tidskriftsartikel (refereegranskat)abstract
- Electron transfer between the enzyme cellobiose dehydrogenase (CDH) and a flavin adenine dinucleotide (FAD) containing a catalytic active fragment of CDH (FAD-fragment) and a graphite electrode, respectively, was established. The current response in the presence of the enzyme substrate for graphite electrodes with CDH or the FAD-fragment adsorbed on the freshly polished graphite surface were compared with that of electrodes where CDH or the FAD-fragment were crosslinked in a redox polymer at the electrode surface. The initial slope, dj/d[S](S=0), where j is the current density and [S](S=0) the zero substrate concentration, was taken as a measure of the substrate response. For the electrodes with enzymes adsorbed directly on the surface, dj/d[S](S=0), was a factor of 3 lower than for electrodes prepared with the polymer mixture. The redox polymer based electrodes, with CDH and with FAD-fragment, both showed a high and close to equal substrate response. In contrast the surface adsorbed CDH gave a much higher substrate response than the FAD-fragment.
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| 12. |
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| 13. |
- Lutz, Mareike, 1967-, et al.
(författare)
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Effects of different additives on a tyrosinase based carbon paste electrode
- 1995
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Ingår i: Analytica Chimica Acta. - Amsterdam : Elsevier. - 0003-2670 .- 1873-4324. ; 305:1-3, s. 8-17
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Tidskriftsartikel (refereegranskat)abstract
- The influence of a number of solid and chemical additives on the sensitivity and operational stability of a tyrosinase carbon paste electrode was studied. Cyclic voltammograms were run of the electrochemically active catechol/o-quinone couple on unmodified and additive modified carbon paste electrodes without tyrosinase. This was done in order to study the influence of these additives on the pure electrochemistry of the carbon paste. The influence on the total system (additive and enzyme modified carbon paste electrode) was studied in the flow injection mode. In some instances a dramatic improvement of the direct electron transfer of the catechol/o-quinone couple was obtained with both solid and chemical additives included in the carbon paste. A similar improvement of biosensor sensitivity in the flow injection mode was obtained with most chemical additives whereas the solid additives had a negative impact on biosensor sensitivity. The results obtained in this work indicate that these additives influence the purely electrochemical processes at the carbon paste and/or the performance of the enzyme in the carbon paste environment. How and why these additives can possibly influence the biosensor performance are discussed. © 1995.
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| 14. |
- Rodushkin, Ilya, et al.
(författare)
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Comparison of two digestion methods for elemental determinations in plant material by ICP techniques
- 1999
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Ingår i: Analytica Chimica Acta. - 0003-2670 .- 1873-4324. ; 378:1-3, s. 191-200
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Tidskriftsartikel (refereegranskat)abstract
- Two digestion procedures have been tested on plant samples for application in the determination of a wide range of major, minor, and trace elements by a combination of inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS). The first is an open-vessel digestion with concentrated nitric acid and the second is a microwave digestion with a mixture of concentrated nitric acid and hydrogen peroxide. The detection limits were found to be controlled by instrumental capabilities in ICP-AES and by digestion blank levels in ICP-MS. The accuracy of the overall analytical procedures was estimated by analysis of a certified reference material. Among elements for which certified concentrations are available, good agreement between measured and reference values was found for 15 and 16 elements in the first and second procedure, respectively. The precision was assessed from replicate analysis (including sample preparation) of reference material and a number of environmental samples and was found to be 5% RSD or better when analyte concentration exceeds quantification limit. Owing to the multielemental capabilities and to the wide analytical range of the ICP techniques used, more than 30 elements can be determined in plant materials at concentrations varying from tens of pg g-1 to wt%.
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| 15. |
- Simpson, S L, et al.
(författare)
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Flow injection determination of Al3+ and Al13O4(OH)(24)(H2O)(12)(7+) species using a 1.3-s reaction with 8-quinolinol-derivatised Fractogel
- 1997
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Ingår i: Analytica Chimica Acta. - 0003-2670 .- 1873-4324. ; 343:1-2, s. 19-32
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Tidskriftsartikel (refereegranskat)abstract
- Speciation of Al is determined by a 1.3-s reaction with 8-quinolinol (oxine)-derivatised Fractogel in a 22 μl column reactor in a flow injection (FI) manifold. Al (pre)concentrated on the column from a 650 μl sample is selectively eluted with 250 μl of 0.02 M NaOH and detected spectrophotometrically as the Al-chrome azurol S (CAS) complex at pH 5.0. This Al (referred to as ‘free Al’) comprises Al3+ + A1(OH)2+ + Al in very labile complexes. Tests with synthetic solutions established that Al is not significantly sequestered from the citrate, oxalate and malonate complexes. Al-hydroxo polymers [Al13(OH)327+] are quantitatively retained by the column but are not desorbed by 0.02 M NaOH in the time frame of the FI method; therefore they do not contribute to the analytical signal. However, they can be quantified after stopped-flow elution with 0.2 M NaOH. The AlF2+ and AlF2+ complexes are retained and eluted quantitatively and therefore contribute to the measurement of ‘free Al’. The method has been applied to humic waters and soil solutions and the results for ‘free’ Al3+ compared with those obtained by the 7-s CAS method. The method has a 2σ detection limit of 70 nM, a linear working range of 0.3–16 μM and relative standard deviations of 7% and 1% at 0.5 and 16 μM, respectively.
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| 16. |
- Simpson, S L, et al.
(författare)
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Kinetic and thermodynamic considerations in the determination of aluminium using pyrocatechol violet : implications for the use of 'kinetic-based' determinations of metal ions in natural systems
- 1998
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Ingår i: Analytica Chimica Acta. - 0003-2670 .- 1873-4324. ; 359:3, s. 329-340
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Tidskriftsartikel (refereegranskat)abstract
- Kinetic and thermodynamic factors associated with the use of pyrocatechol violet (PCV) for the determination of total reactive Al or `free' Al[Al3++Al(OH)2++Al(OH)+2] have been investigated. The rate of reaction of Al with PCV (in MES buffer, pH 6.2) was strongly influenced by the presence of competing ligands. The rate of formation of Al(PCV)2 on the addition of Al3+ to a PCV–competing ligand mixture was: oxalate≈F−≈malonate>salicylate>>no competing ligand>citrate. A similar increase in the reaction rate relative to standards (i.e. no competing ligand) was observed for Al pre-equilibrated in humic waters and soil solution (at concentrations above or below the Al-complexation capacity). The discrepancy in reaction rates may be ascribed to the inhibition through pH-induced hydrolysis of Al3+ in the absence of ligands (i.e. in standards) or to acceleration in the presence of naturally occurring ligands. It has serious implications for the use of kinetic-based FIA protocols for the determination of Al fractions or total Al in natural waters. Specifically, the (usually) slower reaction for Al3+standards implies that measurements on systems containing organic ligands may overestimate the concentration of `free' or total Al. Quantitative studies on the thermodynamics of the citrate–Al3+–PCV system established that the attainment of equilibrium in the pH range 5.0 to 6.6 required ≈300 min. Thus, determination of total Al by FIA in systems containing this or closely related ligands is not feasible.
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| 17. |
- Bjorefors, F, et al.
(författare)
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Stripping voltammetry at preplated mercury coated microelectrodes in flowing solutions
- 1996
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Ingår i: ANALYTICA CHIMICA ACTA. - : ELSEVIER SCIENCE BV. - 0003-2670. ; 325:1-2, s. 11-24
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Tidskriftsartikel (refereegranskat)abstract
- A flow system is described in which stable preplated mercury coatings on microelectrodes can be obtained due to minimised handling of the electrode and the fact that potentiostatic control can be maintained also between the experiments. Compared to the d
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| 18. |
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| 19. |
- Kroger, S, et al.
(författare)
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Assessment of glucose oxidase behaviour in alcoholic solutions using disposable electrodes
- 1998
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Ingår i: Analytica Chimica Acta. - : Elsevier Science B.V., Amsterdam.. - 0003-2670 .- 1873-4324. ; 368:3, s. 219-231
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Tidskriftsartikel (refereegranskat)abstract
- Solvent resistant screen-printed three-electrode devices were employed to assess the behaviour of free and immobilised glucose oxidase in water-miscible organic solvent/aqueous buffer mixtures. Three alcoholic solvents were examined, methanol, ethanol and isopropanol. A rhodinised-carbon electrocatalyst was employed to facilitate hydrogen peroxide oxidation at a decreased operating potential. The devices had a linear response range of 1-10 mU GOX and allowed detection of down to 2 x 10(-14) mol GOX. The measurement of 0-1 (v/v) glucose in 30% (v/v) ethanol was achieved in 2 min using these highly storage-stable enzyme electrodes. Such devices are likely to have widespread applications in the diagnostic and on-line monitoring fields where rapid analysis in alcoholic matrices is desirable. (C) 1998 Elsevier Science B.V. All rights reserved.
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| 20. |
- Kroger, S, et al.
(författare)
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Solvent-resistant carbon electrodes screen printed onto plastic for use in biosensors
- 1997
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Ingår i: Analytica Chimica Acta. - : Elsevier Science B.V., Amsterdam.. - 0003-2670 .- 1873-4324. ; 347:02-jan
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Tidskriftsartikel (refereegranskat)abstract
- A three electrode design using solvent resistant materials is reported, enabling the production of screen printed electrodes for use in biosensor applications involving water-miscible organic solvents. Heat stabilised polyester sheets were used as base materials in combination with carbon basal tracks and an epoxy-based polymer protective coating. The new electrodes avoid problems with solvent induced baseline shifts displayed by conventional screen-printed electrodes. The material for the underlying basal track has been changed from silver to carbon ink to reduce the number of materials involved in the production and avoid possible interferences. In addition, the design is readily applied in biosensor applications. Different methods for the incorporation of a rhodium catalyst are discussed. The application of the electrode system modified with the rhodium catalyst for the amperometric detection of hydrogen peroxide in different concentrations of methanol, isopropanol and ethanol is demonstrated.
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| 21. |
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| 22. |
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| 23. |
- Nyholm, L, et al.
(författare)
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Stability of preplated mercury coated platinum and carbon fibre microelectrodes
- 1996
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Ingår i: ANALYTICA CHIMICA ACTA. - : ELSEVIER SCIENCE BV. - 0003-2670. ; 327:3, s. 211-222
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Tidskriftsartikel (refereegranskat)abstract
- The stability of preplated mercury coatings on platinum and carbon fibre microelectrodes has been studied both after transfer of the electrodes to a mercury free solution and at open circuit in Hg(I) and Hg(II) solutions. While significant amounts of mer
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| 24. |
- Palchetti, I, et al.
(författare)
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Determination of anticholinesterase pesticides in real samples using a disposable biosensor
- 1997
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Ingår i: Analytica Chimica Acta. - : Elsevier Science B.V., Amsterdam.. - 0003-2670 .- 1873-4324. ; 337:3, s. 315-321
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Tidskriftsartikel (refereegranskat)abstract
- A choline amperometric biosensor based on screen-printed electrodes was assembled and used to assess the inhibitory effect of organophosphorus and carbamic pesticides on acetylcholinesterase activity both in standard solutions and real samples, Acetylcholinesterase catalyses the cleavage of acetylcholine to choline and acetate, therefore the amount of choline measured using the biosensor is directly related to the enzyme activity. The extent of enzyme inhibition can be used as an index of the amount of anticholinesterase pesticides present. The hydrophobicity of organophosphorus and carbamic pesticides led to the evaluation of organic, water miscible solvents for use in the proposed method. Berate buffer containing 1% v/v acetonitrile was selected since it exhibited the least influence on enzyme activity from the tested solvents (acetonitrile, acetone, tetrahydrofuran and ethylacetate). Other solvents (dimethylsulfoxide and methanol) were avoided as they exhibited electrochemical interferences. An inhibition calibration curve was obtained using carbofuran, a strong inhibitor of acetylcholinesterase. The lowest detectable standard solution (mean +/-3 standard deviation of the blank) was 2 mu gl(-1) following an incubation time of 10 min. The method was then applied to real samples (fruits and vegetables) showing its suitability as a rapid screening assay (12 min per test) for the assessment of anticholinesterase pesticides, The biosensor results were compared with a standard analytical technique (gas chromatography with nitrogen phosphorus detector, GC-NPD).
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| 25. |
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| 26. |
- Wallenborg, SR, et al.
(författare)
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A microelectrochemical detector for use at low linear velocities in capillary column systems
- 1997
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Ingår i: ANALYTICA CHIMICA ACTA. - : ELSEVIER SCIENCE BV. - 0003-2670. ; 344:1-2, s. 77-85
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Tidskriftsartikel (refereegranskat)abstract
- An end-column microelectrochemical detector, based on a 25 mu m platinum electrode, was used in miniaturised flow and separation systems, at linear mobile phase velocities below 0.1 cm s(-1) (i.e. a volumetric flow of a few mu l min(-1) for a 200 mu m i
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| 27. |
- White, SF, et al.
(författare)
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Development of a mass-producible glucose biosensor and flow-injection analysis system suitable for on-line monitoring during fermentations
- 1996
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Ingår i: Analytica Chimica Acta. - : Elsevier Science B.V., Amsterdam.. - 0003-2670 .- 1873-4324. ; 321:03-feb, s. 165-172
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Tidskriftsartikel (refereegranskat)abstract
- Screen printed amperometric glucose biosensors were constructed and optimised for use in a flow injection analysis (FIA) system. The sensors were fabricated using a catalytic metallised carbon based ink, allowing a working potential of +350 mV (Ag/AgCl). Overall the sensors displayed a high degree of reliability and robustness. A linear response was obtained over the range 0.1 to 25 mM glucose with a slope of 1.35 +/- 0.20 mu A/mM. The within electrode coefficient of variation at each concentration tested (n = 10) was less than 2% (or 0.1 mM for concentrations below 5 mM). In addition, it was demonstrated that a single sensor can be used in the FIA system over a seven day period indicating a high level of operational stability. These sensors fulfil the criteria necessary for a mass produced device, which would be suitable for the on-line monitoring of glucose consumption during microbial fermentation.
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