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1.
An improvement of the peak parking technique is described for the serial determination of cations (Na+, , K+, Mg2+, and Ca2+) and anions (Cl−, , and ) using a single pump, a single eluent and a single detector. The present system used commercially-available unmodified cation
exchange and anion exchange columns, which were attached to each switching valve. When 1.75 mM 5-sulfosalicylic acid was
used as the eluent, serial separation of the above cations and anions was achieved in less than 20 min. The proposed ion chromatographic
method was successfully applied to the serial determination of cations and anions in tap water and river water samples. The
limits of detection at S/N=3 for an injection of 20 μl were 16–68 ppb (μg/l) for cations and 15–28 ppb for anions. 相似文献
2.
A chemiluminescent (CL) detection method has been developed for DNA hybridization. The assay relies on a sandwich-type DNA
hybridization in which gold nanoparticles modified with alkylthiol-capped oligonucleotide strands are used as probes to monitor
the presence of the specific target DNA. The , which is the dissolving product of the gold nanoparticles anchored on the DNA hybrids, serves as an analyte in the H2O2–luminol– CL reaction for the indirect measurement of the target DNA. The combination of the remarkable sensitivity of the CL analysis
with the large number of released from each DNA hybrid allows a detection limit at levels as low as 0.1 pM of the target DNA. Moreover, with a further
silver amplification step, the detection limit will be pushed down to the femtomolar domain.
相似文献
3.
Virender K. Sharma Fabien Casteran Frank J. Millero Concetta De Stefano 《Journal of solution chemistry》2002,31(10):783-792
The sulfur-containing biomolecule, cysteine has a role in physiological and natural environment because of its strong interactions with metals. To understand these interactions of metals with cysteine, one needs reliable dissociation constants for the protonated cysteine species [
CH(CH2SH)COOH; H3B+]. The values of dissociated constants, p
, for protonated cysteine species (H3B+ H+ + H2B, K
1; H2B H+ + HB–,K
2; HB– H+ + B2–,K
3) were determined from potentiometric measurements in NaCl solutions as a function of ionic strength, 0.5–6.0 mol-(kgH2O)–1 and between 5, and 45°C. The equations
were fitted to the results with a standard errors of the fits of 0.116, 0.057, and 0.093 for
,
, and
, respectively. The
results were used to determine new Pitzer parameters (0, 1, and C) for the interactions of Na+ and Cl– with cysteine species. These coefficients can be used to make reasonable estimates of the activity coefficients of the cysteine species and
for the dissociation of cysteine in physiological and natural waters containing mostly NaCl. 相似文献
4.
Potentiometric properties of manganese oxides doped with alkali metal ions (Na+, K+, Rb+ and Cs+), which were prepared by heating mixed solutions (starting solution) of each alkali metal and Mn2+ ions, were examined. Electrodes based on mixed phases of Nao44MnO2/Mn2O3 and hollandite KMn8O16/M2O3 found by X-ray powder diffraction (XRD) exhibited Na+- and K+-selective responses with a near-Nernstian slope, respectively, when the molar ratio of alkali metal ion to Mn2+ ion in the starting solution was 0.1. When no alkali metal ions were added in the manganese oxide films, no significant potentiometric response was observed to any alkali metal ions. The selectivity coefficients of these electrodes were
= 6.7 × 10–2,
= 7.1 × 10–3,
< 9 × 10–4 and
< 9x 10–4 for the Na0.44MnO2/Mn2O3, and
<4 × 10–4
<4x 10–4,
=60 × 10–2 ×10–4,
< 4 × 10–4, for the KMn8O16/Mn2O3, respectively. Electrodes based on manganese oxides made from mixed solutions of Rb+/Mn2+ and Cs+/Mn2+ also responded to the respective primary ions, that is, Rb+ and Cs+ ions, although XRD patterns for the manganese oxides thus made did not show any peaks except for Mn2O3 (bixbyite); it was concluded in these cases that some amorphous type manganese oxides were formed in the Rb+/Mn2+ and Cs+/Mn2+ systems and they responded to the respective ions. Conditioning of these electrodes in an aerated indifferent electrolyte solution, 0.1M tetramethylammonium nitrate (TMA-NO3), for relatively long time, typically more than 2 hours, was found to be a prerequisite for near-Nernstian response to the respective alkali metal ions. During this electrode conditioning, vacant sites (template) suitable in size for selective uptake of primary ions seemed to be formed by releasing the doped alkali metal ions from the solid phase into the adjacent electrolyte solution accompanying oxidation of the manganese oxide film. 相似文献
5.
The structure and decomposition of the [C7H7]+ ions produced by electron-impact from o-, m- and p-chlorotoluene, o-, m- and p-bromotoluence, and p-iodotoluence, have been investigated. By determining the relative abundance of normal and metastable ions, these [C7H7]+ ions at electron energy of 20 eV are shown to be so-called ‘tropylium ions’. The amount of the internal energy of the [C7H7]+ ion estimated by the relative ion abundance ratios, ? [C5H5]+/[C7H7]+ and m*/[C7H7]+ for the decomposition \documentclass{article}\pagestyle{empty}\begin{document}$ [{\rm C}_{\rm 7} {\rm H}_{\rm 7}]^ + \mathop \to \limits^{m^* } [{\rm C}_{\rm 5} {\rm H}_{\rm 5}]^ + + {\rm C}_{\rm 2} {\rm H}_{\rm 2} $\end{document}, is in the order iodotoluene > bromotoluene > chlorotoluene. The heats of formation of the activated complexes for the reaction \documentclass{article}\pagestyle{empty}\begin{document}$ [{\rm C}_{\rm 7} {\rm H}_{\rm 7}]^ + \mathop \to \limits^{m^* } [{\rm C}_{\rm 5} {\rm H}_{\rm 5}]^ + + {\rm C}_{\rm 2} {\rm H}_{\rm 2} $\end{document} were estimated. The values suggest that the decomposing [C7H7]+ ions from various halogenotoluenes are identical in structure. 相似文献
6.
Motivated by recent work on the Ruddlesden–Popper material, which was shown to be a superior oxide-ion conductor than conventional solid-oxide fuel cell cathode perovskite materials,
we undertook A- and B-site doping studies of the Ruddlesden–Popper nickelate series in an attempt to identify other candidates
for cathode application. In this paper, we summarize our most significant results for the and systems and more recently, the higher-order Ruddlesden–Popper phases La
n+1Ni
n
O3n+1 (n=2 and 3), which show greater promise as cathode materials than the n=1 compositions. 相似文献
7.
Thermal membrane potentials across the perfluorosulfonic acid-type membrane, Flemion S, were measured for HCl, alkali metal chlorides, and ammonium and methyl ammonium chlorides. The difference between the mean molar transported entropy of the counterions in the membrane and the partial molar entropy of the counterions in the external solution
was determined from the experimental data on thermal membrane potential, thermoosmosis and electroosmosis. The sign of the thermal membrane potential in HCl solution varies from positive to negative with the concentration. In HCl and alkali metal chloride solutions, the order of their thermal membrane potentials (–/T) is H+>Li+=Na+>K+ which is roughly the inverse of that of the crystallographic radii of the ions. However, the order of their entropy differences
is H+>Na+>K+>Li+ which is just the inverse of that of their thermoosmotic coefficients (D) or the entropy difference of water
in thermoosmosis. For the ammonium and methyl ammonium ion forms, the orders of both –/T and
increase with an increasing number of methyl groups: (CH3)4N+>(CH3)3NH+>(CH3)2NH
2
+
> CH3NH
3
+
>NH
4
+
, which is also the inverse of that ofD or
. 相似文献
8.
Kinetics and equilibria for the formation of a 1:1 complex between palladium(II) and chloroacetate were studied by spectrophotometric measurements in 1.00 mol HClO4 at 298.2 K. The equilibrium constant, K, of the reaction
was determined from multi-wavelength absorbance measurements of equilibrated solutions at variable temperatures as log 0.006 with and , and spectra of individual species were calculated. Variable-temperature kinetic measurements gave rate constants for the forward and backward reactions at 298.2 K and ionic strength 1.00 mol as and , with activation parameters and , respectively. From the kinetics of the forward and reverse processes, and were derived in good agreement with the results of the equilibrium measurements. Specific Ion Interaction Theory was employed for determination of thermodynamic equilibrium constants for the protonation of chloroacetate () and formation of the PdL+ complex (). Specific ion interaction coefficients were derived. 相似文献
9.
Iron ions are shown to play a special role among transition metal ions in the oxidation of sulfite by oxygen. The thermodynamically favorable formation of chain carriers S
: FeOH2++ HSO3
– Fe2++ H2O +
, H
r
298
0 –250 kJ/mol accompanied by the regeneration of the active Fe(III) form in the reactions of Fe(II) with
and HSO5
–provides the efficient catalytic mechanism for sulfite consumption even at [Fe]0 10–8mol/l. Any aqueous solution contains iron ions in this amounts. Thus, the noncatalytic oxidation of sulfite is in fact the catalytic reaction involving unavoidable microadmixtures of iron ions. Other transition metal ions (Mn2+, Co2+, etc.) can only enhance the catalytic effect of iron admixture. 相似文献
10.
The oxidation of H2NOH is first-order both in [NH3OH+] and [AuCl4
–]. The rate is increased by the increase in [Cl–] and decreased with increase in [H+]. The stoichiometry ratio, [NH3OH+]/[AuCl4
–], is 1. The mechanism consists of the following reactions.
The rate law deduced from the reactions (i)–(iv) is given by Equation (v) considering that [H+] K
a.
The reaction (iii) is a combination of the following reactions:
The activation parameters for the reactions (ii) and (iii) are consistent with an outer-sphere electron transfer mechanism. 相似文献
11.
New far-visible absorbing anilino-cyanine dyes have been synthesised for future application as chromoionophores in integrated
waveguide absorbance optodes based on bulk optodes. The effect of the heterocycle, of the substitution of the heterocyclic
nitrogen and of the type of heptamethine central ring on the pK
a
values (4.3–8.2 in ethanol–water solutions and 9.5–11.0 in plasticised PVC membranes), on the spectroscopic characteristics
of the dye and on photostability is discussed. pH-selective bulk optodes have been formulated as a first approach to develop
ion-selective optodes, and sensitivity, repeatability, lifetime and response time have been determined. The dyes show good
analytical behaviour for use as chromoionophores for the development of ion-selective optodes. Reversible (80–87%), fast (tr90% = 0.94–2.28 min) and pH-sensitive membranes (slopes of 0.09–0.23 ΔAbs·pHdec–1, absorbance range 0.19–0.53) have been obtained. Moreover, they exhibit good spectroscopic features for employment with integrated
optochemical sensors: absorption maxima of the acidic species in plasticised PVC membranes matched those of 650–670-nm LEDs,
high molar absorption coefficients ( L mol–1 cm–1 and L mol−1 cm−1) and fluorescence.
Absorption spectra of the acidic and basic structures of one of the synthesised chromoionophores at different pKa values.
Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users. 相似文献
12.
G. Wiese und B. Thiele 《Fresenius' Journal of Analytical Chemistry》1978,289(4):272-274
Zusammenfassung Die für eine Verwendung in wäß-rigem Medium erarbeitete Schnellmethode wird auf organische Lösungsmittel (Methanol) übertragen. Mit Hilfe statistischer Prüfmethoden wird gezeigt, daß für die Reaktion des Typs: Z–NH2+HCl Z–NH3
++Cl– (Z–NH2: Propylamin, Anilin, Piperidin) unter den Verfahrensbedingungen der Schnellmethode in methanolischer Lösung eine Äquivalenzpunktbestimmung mit hinreichender Genauigkeit möglich ist [Prozentualer Fehler von
] und daß zwischen Langzeit- und Schnellmethode kein signifikanter Genauigkeitsunterschied besteht.Wir danken dem Fonds der Chemischen Industrie für die finanzielle Unterstützung dieser Arbeit. 相似文献
13.
Determination of norfloxacin in human urine by capillary electrophoresis with electrochemiluminescence detection 总被引:3,自引:0,他引:3
A fast and sensitive approach that can be used to detect norfloxacin in human urine using capillary electrophoresis with end-column
electrochemiluminescence (ECL) detection of is described. The separation column was a 75-μm i.d. capillary. The running buffer was 15 mmol L−1 sodium phosphate (pH 8.2). The solution in the detection cell was 50 mmol L−1 sodium phosphate (pH 8.0) and 5 mmol L−1
The ECL intensity varied linearly with norfloxacin concentration from 0.05 to 10 μmol L−1. The detection limit (S/N=3) was 0.0048 μmol L−1, and the relative standard deviations of the ECL intensity and the migration time for eleven consecutive injections of 1.0 μmol L−1 norfloxacin (n=11) were 2.6% and 0.8%, respectively. The method was successfully applied to the determination of norfloxacin spiked in human
urine without sample pretreatment. The recoveries were 92.7–97.9%.
相似文献
14.
The mechanism of the Co(II) catalytic electroreduction of water insoluble CoR2 salt in the presence of cysteine was developed. CoR2 = cobalt(II) cyclohexylbutyrate is the component of a carbon paste electrode. Electrode surface consecutive reactions are:
(a) fast (equilibrium) reaction of the complex formation, (b) rate-determining reversible reaction of the promoting process of CoR(Ac+) complex formation, (c) rate-determining irreversible reaction of the electroactive complex formation with ligand-induced adsorption, and (d) fast irreversible reaction of the electroreduction. Reactions (a,b) connected with CoR2 dissolution and reactions (c,d) connected with CoR2 electroreduction are catalyzed by . Regeneration of (reactions “b,d”) and accumulation of atomic Co(0) (reaction “d”) take place. Experimental data [Sugawara et al., Bioelectrochem
Bioenergetics 26:469, 1991]: i
a vs E (i
a is anodic peak, E is cathodic accumulation potential), i
a vs , and i
a vs pH have been quantitatively explained. 相似文献
15.
Let λ1 (G) and Δ (G), respectively, denote the largest eigenvalue and the maximum degree of a graph G. Let
be the set of trees with perfect matchings on 2m vertices, and
. Among the trees in
, we characterize the tree which alone minimizes the largest eigenvalue, as well as the tree which alone maximizes the largest
eigenvalue when
. Furthermore, it is proved that, for two trees T
1 and T
2 in
(m≥ 4), if
and Δ (T
1) > Δ (T
2), then λ1 (T
1) > λ1 (T
2). 相似文献
16.
Martens T Bogaerts A Brok W van Dijk J 《Analytical and bioanalytical chemistry》2007,388(8):1583-1594
A model developed for a dielectric barrier discharge (DBD) in helium, used as a new spectroscopic source in analytical chemistry,
is presented in this paper. The model is based on the fluid approach and describes the behavior of electrons, He+ and ions, He metastable atoms, He atoms in higher excited levels, and He2 dimers. The He ground-state atoms are regarded as background gas. The characteristic effect of charging/discharging of the
dielectrics which cover both electrodes is also simulated. Typical results of the model include the distribution of potential
inside the plasma (and the potential drop across the dielectrics), the electric current and gap voltage as a function of time
for a given applied potential profile, the spatial and temporal number-density profiles of the different plasma species, and
the relative contributions of the mechanisms of their production and loss.
Figure Schematic diagram of the dielectric barrier discharge (left) and typical temporal profiles of voltage and current, as obtained
from the simulations (right) 相似文献
17.
Richard D. Bowen Dudley H. Williams G. Hvistendahl John R. Kalman 《Journal of mass spectrometry : JMS》1978,13(12):721-728
The unimolecular decompositions of two isomers of [C3H8N]+, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm CH}_{\rm 2} {\rm CH} = \mathop {\rm N}\limits^ + {\rm H}_2 $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm CH}_{\rm 2} \mathop {\rm N}\limits^ + {\rm H = CH}_{\rm 2} $\end{document}, are discussed in terms of the potential energy profile over which reaction may be considered to occur. The energy needed to promote slow (metastable) dissociations of either ion is found to be less than that required to cause isomerization to the other structure. This finding is supported by the observation of different decomposition pathways, different metastable peak shapes for C2H4 loss, the results of 2H labelling studies, and energy measurements on the two ions. The corresponding potential energy profile for decomposition of the oxygen analogues, \documentclass{article}\pagestyle{empty}\begin{document}${\rm CH}_{\rm 3} {\rm CH}_{\rm 2} {\rm CH =\!= }\mathop {\rm O}\limits^ + {\rm H} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm CH}_{\rm 2} \mathop {\rm O}\limits^ + {\rm = CH}_{\rm 2} $\end{document}, is compared and contrasted with that proposed for the [C3H8N]+ isomers. This analysis indicates that for the oxygen analogues, the energy needed to decompose either ion is very similar to that required to cause isomerization to the other structure. Consequently, dissociation of either ion is finely balanced with rearrangement to the other and similar reactions are observed. Detailed mechanisms are proposed for loss of H2O and C2H4 from each ion and it is shown that these mechanisms are consistent with 2H and 13C labelling studies, the kinetic energy release associated with each decomposition channel, the relative competition between H2O and C2H4 loss and energy measurements. 相似文献
18.
The kinetics of the formation and decomposition of water-soluble colloidal MnO2 in the paracetamol– redox system have been investigated spectrophotometrically in aqueous-neutral media at 30 °C. Upon mixing aqueous solutions of permanganate and paracetamol, a readily distinguishable brown color appears and then disappears slowly. Experiments have been done to confirm the nature of intermediate (Mn(IV)) formed during the reduction of permanganate by paracetamol. The stoichiometry was found to be 1:1. Formation and decomposition of water-soluble colloidal MnO2 depend upon the experimental conditions, i.e., [paracetamol] and [H+]. The effect of total [paracetamol], and [H+] on the rate of the reaction was determined. On the basis of various observations, two mechanisms are proposed: one for MnO2 formation and the other for decomposition. 相似文献
19.
20.
Nanostructured electrochemical DNA biosensors for detection of the effect of berberine on DNA from cancer cells 总被引:2,自引:0,他引:2
Ovádeková R Jantová S Letasiová S Stepánek I Labuda J 《Analytical and bioanalytical chemistry》2006,386(7-8):2055-2062
Multi walled carbon nanotubes (MWNT) in dimethylformamide (DMF) or aqueous sodium dodecyl sulfate (SDS) solution, colloidal
gold nanoparticles (GNP) in phosphate buffer solution (PBS), and a GNP–MWNT mixture in aqueous SDS solution have been investigated
for chemical modification of a screen-printed carbon electrode used as the signal transducer of a dsDNA-based biosensor. Differential
pulse voltammetry of the DNA redox marker and the guanine moiety anodic oxidation and cyclic voltammetry with K3[Fe(CN)6] as indicator revealed substantial enhancement of the response of the biosensor, particularly when MWNT in SDS solution was
used. The biosensor was used in testing of berberine, an isoquinoline plant alkaloid with significant antimicrobial and anticancer
activity. Berberine had a very strong, concentration-dependent, effect on the structural stability of DNA from the human cancer
cells (U937 cells) whereas non-cancer cells were changed only when berberine concentrations were relatively high 75 and 50 μg
mL−1.
Figure Schematic illustration of preparation of the nanostructured films: (a) layer-to-layer coverage (DNA/nanomaterial/SPE); (b) mixed coverage (DNA-nanomaterial/SPE) 相似文献