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21.
A flow-through voltammetric cell with a hanging mercury drop electrode has been developed to fit the static mercury drop electrode (PAR 303). The design has resulted in a linear increase of sensitivity with flow rate and an enhancement of sensitivity by the wall-jet effect. The cell is used in a flow injection system in which samples are introduced with a R??i?ka—Hansen injector. The mercury drop is held at plating potentials while the sample peak passes through the cell. Stripping is done under stopped flow conditions, to reduce noise, after the sample has been washed completely from the cell. The stripping thus takes place into the carrier electrolyte which always has a constant composition independent of sample constituents. Film-forming interfering species will, however, remain on the surface of the mercury drop. The effect of medium exchange on films produced by l-cysteine is reported. The flow-through medium exchange simplifies deaeration, speeds up analysis and reduces contamination. 相似文献
22.
Kessel L Kalinin S Nagaraj RH Larsen M Johansson LB 《Photochemistry and photobiology》2002,76(5):549-554
The intrinsic fluorescence from the human lens on excitation in the UV region, referred to as blue lens autofluorescence, increases with age or in the presence of diabetes. The present study reveals that the relative contribution of compounds responsible for the blue autofluorescence appears to be a constant with age. Three potential candidates for the blue fluorescence were also studied with respect to fluorescence spectroscopic properties. These were argpyrimidine and pentosidine, both advanced glycation end products, and 3-hydroxykynurenine (3-OH-kynurenine), a photooxidative derivative of tryptophan. It was shown that the spectral properties of argpyrimidine and pentosidine are compatible with the observed blue fluorescence of the human lens, whereas the fluorescence from 3-OH-kynurenine is negligible. 相似文献
23.
Mats Johansson Eva Malmstrm Anders Hult 《Journal of polymer science. Part A, Polymer chemistry》1993,31(3):619-624
A model two-step synthesis of a saturated hyperbranched hydroxyl-terminated ester has been developed to show a synthesis route. Three different series of hyperbranched esters with different terminations have been synthesized to relate some of their properties to their structures. This route has then been used to synthesize three different allyl ethermaleate functional hyperbranched ester resins in a two-step procedure. The resins have been characterized with respect to rheology, structure, and properties, and the differences are discussed. The allyl ether-maleate functional resins have also been studied with respect to curing performance and final film properties. © 1993 John Wiley & Sons, Inc. 相似文献
24.
Testing shelled corn for aflatoxin, Part III: evaluating the performance of aflatoxin sampling plans
Johansson AS Whitaker TB Giesbrecht FG Hagler WM Young JH 《Journal of AOAC International》2000,83(5):1279-1284
The effects of changes in sample size and/or sample acceptance level on the performance of aflatoxin sampling plans for shelled corn were investigated. Six sampling plans were evaluated for a range of sample sizes and sample acceptance levels. For a given sample size, decreasing the sample acceptance level decreases the percentage of lots accepted while increasing the percentage of lots rejected at all aflatoxin concentrations, and decreases the average aflatoxin concentration in lots accepted and lots rejected. For a given sample size where the sample acceptance level decreases relative to a fixed regulatory guideline, the number of false positives increases and the number of false negatives decreases. For a given sample size where the sample acceptance level increases relative to a fixed regulatory guideline, the number of false positives decreases and the number of false negatives increases. For a given sample acceptance level, increasing the sample size increases the percentage of lots accepted at concentrations below the regulatory guideline while increasing the percentage of lots rejected at concentrations above the regulatory guideline, and decreases the average aflatoxin concentration in the lots accepted while increasing the average aflatoxin concentration in the rejected lots. For a given sample acceptance level that equals the regulatory guideline, increasing the sample size decreases misclassification of lots, both false positives and false negatives. 相似文献
25.
Johansson A Abrahamsson M Magnuson A Huang P Mårtensson J Styring S Hammarström L Sun L Akermark B 《Inorganic chemistry》2003,42(23):7502-7511
The preparation of donor (D)-photosensitizer (S) arrays, consisting of a manganese complex as D and a ruthenium tris(bipyridyl) complex as S has been pursued. Two new ruthenium complexes containing coordinating sites for one (2a) and two manganese ions (3a) were prepared in order to provide models for the donor side of photosystem II in green plants. The manganese coordinating site consists of bridging and terminal phenolate as well as terminal pyridyl ligands. The corresponding ruthenium-manganese complexes, a manganese monomer 2b and dimer 3b, were obtained. For the dimer 3b, our data suggest that intramolecular electron transfer from manganese to photogenerated ruthenium(III) is fast, k(ET) > 5 x 10(7) s(-)(1). 相似文献
26.
The coordination around the thorium(IV) ion in aqueous perchlorate, chloride and nitrate solutions has been determined from large angle X-ray scattering measurements. In perchlorate solutions, where inner-sphere complexes are not formed, the first coordination sphere contains 8.0±0.5 water molecules with Th-H2O bond lengths of 2.485 Å. In chloride solutions inner-sphere complexes are formed, which lead to an increase in the coordination number. In nitrate solutions the nitrate ions are bonded as bidentate ligands to the thorium ion. The bond lengths are similar to those found in crystalline hydrates of thorium nitrate. The coordination numbers found for thorium(IV) in solution are compared with previously reported values for lower charged ions of similar size.On leave from Department of Inorganic Chemistry Royal Institute of Technology S-10044 Stockholm Sweden 相似文献
27.
Hisanobu Wakita Georg Johansson Magnus Sandström Peter L. Goggin Hitoshi Ohtaki 《Journal of solution chemistry》1991,20(7):643-668
Structures of the complexes formed in aqueous solutions between zinc(II) and iodide ions have been determined from large-angle X-ray scattering, Raman and far-IR measurements. The coordination in the hydrated Zn2+ hexaaqua ion and the first iodide complex, [ZnI]+, is octahedral, but is changed into tetrahedral in the higher complexes, [ZnI2(H2O)2], [ZnI3(H2O)]– and [ZnI4]2–. The Zn-I bond length is 2.635(4)Å in the [ZnI4]2– ion and slightly shorter, 2.592(6)Å, in the two lower tetrahedral complexes. In the octahedral [ZnI(H2O)5]+ complex the Zn-I bond length is 2.90(1)Å. The Zn-O bonding distances in the complexes are approximately the same as that in the hydrated Zn2+ ion, 2.10(1)Å. 相似文献
28.
Adams RD Captain B Herber RH Johansson M Nowik I Smith JL Smith MD 《Inorganic chemistry》2005,44(18):6346-6358
The reaction of Re2(CO)8[mu-eta2-C(H)=C(H)Bu(n)](mu-H) with Ph3SnH at 68 degrees C yielded the new compound Re2(CO)8(mu-SnPh2)2 (10) which contains two SnPh2 ligands bridging two Re(CO)(4) groups, joined by an unusually long Re-Re bond. Fenske-Hall molecular orbital calculations indicate that the bonding in the Re2Sn2 cluster is dominated by strong Re-Sn interactions and that the Re-Re interactions are weak. The 119Sn M?ssbauer spectrum of 10 exhibits a doublet with an isomer shift (IS) of 1.674(12) mm s(-1) and a quadrupole splitting (QS) of 2.080(12) mm s(-1) at 90 K,characteristic of Sn(IV) in a SnA2B2 environment. The IS is temperature dependent, -1.99(14) x 10(-4) mm s(-1) K(-1); the QS is temperature independent. The temperature-dependent properties are consistent with the known Gol'danskii-Kariagin effect. The germanium compound Re2(CO)8(mu-GePh2)2 (11) was obtained from the reaction of Re2(CO)8[mu-eta2-C(H)=C(H)Bu(n)](mu-H) with Ph3GeH. Compound 11 has a structure similar to that of 10. The reaction of 10 with Pd(PBu(t)3)2 at 25 degrees C yielded the bis-Pd(PBu(t)3) adduct, Re2(CO)8(mu-SnPh2)2[Pd(PBu(t)3)]2 (12); it has two Pd(PBu(t)3) groups bridging two of the four Re-Sn bonds in 10. Fenske-Hall molecular orbital calculations show that the Pd(PBu(t)3) groups form three-center two-electron bonds with the neighboring rhenium and tin atoms. The mono- and bis-Pt(PBu(t)3) adducts, Re2(CO)8(mu-SnPh2(2)[Pt(PBu(t)3)] (13) and Re2(CO)8(mu-SnPh2)2[Pt(PBu(t)3)]2 (14), were formed when 10 was treated with Pt(PBu(t)3)2. A mono adduct of 11, Re2(CO)8(mu-GePh2)2[Pt(PBu(t)3)] (15), was obtained similarly from the reaction of 11 with Pt(PBu(t)3)2. 相似文献
29.
S. P. Nielsen A. Aarkrog P. A. Colgan E. McGee H. J. Synnott K. J. Johansson A. D. Horrill V. H. Kennedy N. Barbayiannis 《Journal of Radioanalytical and Nuclear Chemistry》1993,171(2):303-317
An intercomparison of sampling procedures used by five laboratories for the determination of radiocaesium in vegetation and peaty soil was carried out at two locations in Cumbria. The multiple sampling has given information on the homogeneity of the parameters studied at each location. The parameters comprise soil bulk densities, total deposition of137Cs, deposition of137Cs in three soil layers, biomass densities, concentrations of137Cs in pasture, and activity ratios (134Cs/137Cs) in soil and vegetation. The determination of total deposition of137Cs gave no indication of differences between the laboratories. The results from the soil profiles do indicate significant differences between laboratories. One laboratory using a coring technique observed difficulties during sampling due to compression of the soil. The coring technique should thus be avoided or applied with extreme care for the sampling of depth profiles in peaty soil. The results from the sampling of pasture show no indication of differences between the laboratories. For the parameters studied the observed variabilities across soil depths and locations range from 10% to 81% in terms of relative standard deviations. A comparison across all results at the two locations indicate a 50% higher field variability at one of the sites relative to the other. 相似文献
30.
I M Johansson E C Huang J D Henion J Zweigenbaum 《Journal of chromatography. A》1991,554(1-2):311-327
On-line capillary electrophoresis (CE) separations are shown for a synthetic peptide mixture and a tryptic digest of human hemoglobin in an uncoated fused-silica capillary with detection using atmospheric pressure ionization mass spectrometry (API-MS). The CE system utilized a 1-m capillary column of either 75- or 100-microns I.D. These somewhat larger inside diameters allow higher sample capacities for MS detection and the 1-m length facilitates connecting the CE column to the liquid junction-ion spray interface and MS system. Low volatile buffer concentrations (15-20 mM) of ammonium acetate or ammonium formate, and high organic modifier content (5-50%) of methanol or acetonitrile facilitates ionization under electrospray conditions. This study shows that peptides separated by CE may be transferred to the API-MS system through a liquid junction coupling to the pneumatically assisted electrospray (ion spray) interface at low buffer pH when the electroosmotic flow is low (0-0.04 microliter/min). CE-MS as described herein is facilitated by features in modern CE instrumentation including robotic cleaning and pressurization of the capillary inlet. The latter is particularly useful for repetitive rinsing and conditioning of the capillary column between analyses in addition to continuous 'infusion' of sample to the mass spectrometer for tuning purposes. In addition to facile molecular weight determination, amino acid sequence information for peptides may be obtained by utilizing on-line tandem MS. After the tryptic digest sample components enter the API-MS system, the molecular ion species of individual peptides may be focussed and transmitted into the collision cell of the tandem triple quadrupole mass spectrometer. Collision-induced dissociation of protonated peptide molecules yielded structural information for their characterization following injection of 10 pmol of a tryptic digest from human hemoglobin. 相似文献