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- KINTNER, PM, et al.
(författare)
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FIRST RESULTS FROM THE FREJA HF SNAPSHOT RECEIVER
- 1995
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Ingår i: GEOPHYSICAL RESEARCH LETTERS. - : AMER GEOPHYSICAL UNION. - 0094-8276. ; 22:3, s. 287-290
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The Freja plasma wave instrument has measured electric field waveforms up to 4 MHz in the auroral ionosphere near 1700 km altitude. The HF snapshot receiver responds to natural signals during every passage through the auroral ionosphere and we have curren
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- 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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- 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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