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1.
We model the evolution of the concentration field of macromolecules in a symmetric field‐flow fractionation (FFF) channel
by a one‐dimensional advection–diffusion equation. The coefficients are precisely determined from the fluid dynamics. This
model gives quantitative predictions of the time of elution of the molecules and the width in time of the concentration pulse.
The model is rigorously supported by centre manifold theory. Errors of the derived model are quantified for improved predictions
if necessary. The advection–diffusion equation is used to find that the optimal condition in a symmetric FFF for the separation
of two species of molecules with similar diffusivities involves a high rate of cross‐flow.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
By anodic oxidation of hydrogen on the Pt ring of a metal-disk-Pt-ring rotating electrode in aqueous acid (pH 0.5–3) sulfate
solutions, it is shown that during the polarization of the metal disk hydrogen coevolves by two parallel reactions. One is
the well known electrochemical charge transfer process, while the other one is a direct chemical reaction of the metal, i.e.
iron, with water molecules from the electrolyte. This process was proposed a long time ago by Kolotyrkin and co-workers, but
their experimental results were subjected to serious criticism which is taken care of in the present paper. The chemical reaction
is potential- and pH-independent and, depending on the actual conditions during the corrosion processes (actual potential,
pH, etc.), can be of greater or smaller importance in the overall process. The consequences of the existence of this direct
chemical reaction of metal with water molecules (i.e. H2O-induced corrosion or chemical corrosion) on pitting and stress corrosion cracking of metals is discussed.
Dedicated to the ninetieth anniversary of Ya.M. Kolotyrkin’s birth.
This article was submitted by the authors in English. 相似文献
3.
A simple and accurate spectrophotometric method is proposed for the determination of tannins in tea and beer samples based on the reduction of iron(III) to iron(II) by tannins at 80 degrees C for 20 min. The iron(II) was then reacted with 1,10-phenanthroline at pH 4.4 to form a coloured complex. Background correction could be effected by precipitating the tannins in the sample solution twice with gelatin and kaolin. Absorbance measurements were made at 540 nm and the calibration graph was linear from 0 to 5.5 micrograms ml-1 of tannic acid with a slope of 0.213 A p.p.m.-1. The precision for the determination of tannins in a tea sample containing 9.45% of tannins was 1.8%. Most of the ingredients commonly found in tea and beer samples do not interfere with the determination. Several tea and beer samples were analysed for their tannin content using the proposed method. 相似文献
4.
H. Namazi M. Adeli Z. Zarnegar S. Jafari A. Dadkhah A. Shukla 《Colloid and polymer science》2007,285(14):1527-1533
Benzyl alcohol and Rose Bengal were loaded and entrapped using linear–dendritic macromolecules by two procedures. In the first
procedure, benzyl alcohol was attached to the end functional groups of linear–dendritic macromolecules by ester bonds to afford
linear–dendritic–host conjugates. In the second procedure, entrapment was based on physical interactions between Rose Bengal
and linear–dendritic macromolecules; this procedure is known as complexation method. Loading and binding capacity of different
linear–dendritic macromolecules was investigated using 1H nuclear magnetic resonance (NMR) and UV spectroscopy methods. It was found the loading or binding capacity of linear–dendritic
macromolecules depends on their generation, so that higher generations have higher loading or binding capacity. Diameter of
nanocarriers was investigated using dynamic light scattering (DLS) experiments, and it was between 16 and 50 nm for different
nanocarriers. Release of guest molecules from nanocarriers was evaluated at pH 1, 7.4, and 10.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
5.
A square wave voltammetric method whith a static mercury drop electrode (SMDE) was developed for the quantitative determination
of iron (III) in Zn-Fe alloy galvanic baths. Real alloy bath samples were analyzed by the standard addition method and recovery
tests were carried out. 0.50 mol L–1 sodium citrate (pH 6.0) or 0.20 mol L–1 oxalic acid (pH 4.0) were applied as supporting electrolytes resulting in both cases in a peak potential of about –0.20 V
vs. Ag|AgCl (saturated KCl). The iron (III) concentration in the alloy bath was 9.0 × 10–4 mol L–1. A good correlation (r = 0.9999) was achieved between the iron (III) concentration and the peak current in the electrolytes
studied, with linear response ranges from 1.0 × 10–6 to 1.2 × 10–4 mol L–1. Interference levels for some metals such as copper (II), lead (II), chromium (III) and manganese (II) that can hinder the
Zn-Fe alloy deposition were evaluated; only copper (II) interferes seriously.
Received: 4 April 2000 / Revised: 19 June 2000 / Accepted: 22 June 2000 相似文献
6.
Beena PS Basheer SM Bhat SG Bahkali AH Chandrasekaran M 《Applied biochemistry and biotechnology》2011,164(5):612-628
Marine Aspergillus awamori BTMFW032, recently reported by us, produce acidophilic tannase as extracellular enzyme. Here, we report the application of
this enzyme for synthesis of propyl gallate by direct transesterification of tannic acid and in tea cream solubilisation besides
the simultaneous production of gallic acid along with tannase under submerged fermentation by this fungus. This acidophilic
tannase enabled synthesis of propyl gallate by direct transesterification of tannic acid using propanol as organic reaction
media under low water conditions. The identity of the product was confirmed with thin layer chromatography and Fourier transform
infrared spectroscopy. It was noted that 699 U/ml of enzyme could give 60% solubilisation of tea cream within 1 h. Enzyme
production medium was optimized adopting Box–Behnken design for simultaneous synthesis of tannase and gallic acid. Process
variables including tannic acid, sodium chloride, ferrous sulphate, dipotassium hydrogen phosphate, incubation period and
agitation were recognized as the critical factors that influenced tannase and gallic acid production. The model obtained predicted
4,824.61 U/ml of tannase and 136.206 μg/ml gallic acid after 48 h of incubation, whereas optimized medium supported 5,085 U/ml
tannase and 372.6 μg/ml of gallic acid production after 36 and 84 h of incubation, respectively, with a 15-fold increase in
both enzyme and gallic acid production. Results indicated scope for utilization of this acidophilic tannase for transesterification
of tannic acid into propyl gallate, tea cream solubilisation and simultaneous production of gallic acid along with tannase. 相似文献
7.
Norbert Stoppacher Fritz Pittner Gerhard Sontag 《Monatshefte für Chemie / Chemical Monthly》2009,140(8):909-914
Abstract In this study a design of an immunosensor for 1-nitropyrene is illustrated. First the response of 1-nitropyrene reduced at
a glassy carbon electrode between 0 and −0.8 V was investigated with respect to pH and solvent. Then polyclonal anti-1-nitropyrene
antibodies isolated from a rabbit antiserum were covalently bound to the surface of the glassy carbon electrode. This modified
electrode was immersed in standard solutions or sample extracts for 5–15 min. 1-Nitropyrene was bound by the antibodies, accumulated
and then analyzed at pH 6.5 in another supporting electrolyte by differential pulse voltammetry. Afterwards the immunosensor
could be regenerated for the next measurement by rinsing with acetonitrile–water (40:60, v/v). A linear response was found between 20 and 100 ng/cm3. The limit of detection was 10 ng/cm3 and the intraday reproducibility of three immunosensors assembled during two months was between 4.5 and 10%. This sensor
was applied to the analysis of 1-nitropyrene in air particulate matter and smoked tea.
Graphical abstract
相似文献
8.
Rapid and sensitive spectrophotometric determination of trace amounts of iron(III) using leuco Xylene cyanol FF 总被引:1,自引:0,他引:1
A new, simple, sensitive, and reliable method is presented for the rapid spectrophotometric determination of trace amounts of iron(III) using leuco Xylene cyanol FF. The method is based on the oxidation of leuco Xylene cyanol FF (LXCFF) to its blue form of xylene cyanol FF by iron(III) in sulfuric acid medium (pH 2.0–3.0), the absorbance of the formed dye is measured in an acetate buffer medium (pH 2.8–4.4) at 615 nm. The method obeys Beer's law over a concentration range of 0.15–0.9 g mL-1 iron, having a molar absorptivity of 5.6×104 L mol-1 cm-1 and a Sandell's sensitivity of 0.0001 g cm-2. The optimum reaction conditions and other analytical parameters have been evaluated. The developed method has been successfully applied to the determination of iron in water, soil, industrial effluent, plant material, pharmaceutical preparations, synthetic mixtures, and aluminum alloys. 相似文献
9.
The chromatographic fractionation of aquatic humic substances (HS) onto iron(III)-coated cellulose (Cell-Fe(III)) as a metal-loaded
adsorbent is described, analogously to the separation principle of the well-established metal affinity chromatography (MAC).
For that purpose the sorption of HS from different aquatic origin on that collector was characterized by their kinetics and
equilibrium distribution coefficients Kd. Based on Kd values of 103 to 104,mL/g, and fast sorption kinetics a preparative HPLC procedure, using stepwise increased pH-values (pH 8–12.5, borate buffer)
as an eluent, was developed for the fractionation of dissolved HS (up to 7 fractions of different amount). The fractions obtained
by this MAC procedure from selected aquatic HS samples were different in their Cu(II) complexation capacity, absorbance ratio
E265 nm/E365 nm and Fourier transform infrared spectra.
Received: 14 June 1999 / Revised: 6 August 1999 / Accepted: 10 August 1999 相似文献
10.
The chromatographic fractionation of aquatic humic substances (HS) onto iron(III)-coated cellulose (Cell-Fe(III)) as a metal-loaded
adsorbent is described, analogously to the separation principle of the well-established metal affinity chromatography (MAC).
For that purpose the sorption of HS from different aquatic origin on that collector was characterized by their kinetics and
equilibrium distribution coefficients Kd. Based on Kd values of 103 to 104,mL/g, and fast sorption kinetics a preparative HPLC procedure, using stepwise increased pH-values (pH 8–12.5, borate buffer)
as an eluent, was developed for the fractionation of dissolved HS (up to 7 fractions of different amount). The fractions obtained
by this MAC procedure from selected aquatic HS samples were different in their Cu(II) complexation capacity, absorbance ratio
E265 nm/E365 nm and Fourier transform infrared spectra.
Received: 14 June 1999 / Revised: 6 August 1999 / Accepted: 10 August 1999 相似文献
11.
A method for the extraction of bioavailable iron from soils from various parts of Slovakia using a buffered diethylenetriaminepentaacetic
acid (DTPA) solution was utilized. The extractant consists of 0.005 mol dm−3 DTPA, 0.1 mol dm−3 CaCl2, and 0.1 mol dm−3 triethanolamine with pH of 7.3. DTPA was selected as the chelating agent because it can effectively extract micronutrient
metal, iron. Distribution of iron in the horizons of various types of soils with respect to bioavailable iron was evaluated.
The bioavailable iron in the extracts was determined by flame atomic absorption spectrometry. The calibration standards were
prepared in the same surroundings as the extracts. Comparing to the average of 2.7–3.7 % total iron contents in Slovak soils,
the available amounts of iron represent in average only very small amounts, approximately 0.3 % in comparison to total amounts. 相似文献
12.
The influence of solution pH on the structure of polyvinyl alcohol adsorption layer on the alumina surface was investigated.
The spectrophotometry, viscosimetry, thermogravimetry, potentiometric titration and microelectrophoresis were applied in experiments.
These methods enable determination of the following parameters: adsorbed amount of PVA, stability of suspension without and
with polymer, thickness of its adsorption layers, changes in thermal characteristics of Al2O3 surface with the adsorbed polymer, surface charge density and zeta potential of solid particles in the presence and absence
of PVA, respectively. All measurements were carried out in the pH range 3–9. The obtained results indicate that pH has a great
influence on the conformation of PVA chains adsorbed on the alumina surface. It is due to incomplete hydrolysis of acetate
groups of polyvinyl alcohol macromolecules (degree of hydrolysis 97.5%), which dissociate with the increasing pH. Moreover,
the polymer adsorption on the alumina surface causes changes in the course of thermogravimetric curves. The effect of weight
loss for Al2O3–PVA systems is smaller than that of Al2O3 without polymer. It is due to elimination of water molecules from the solid surface by adsorbed polymer. 相似文献
13.
Kralj B Krizaj I Bukovec P Slejko S Milacic R 《Analytical and bioanalytical chemistry》2005,383(3):467-475
Speciation of Al in tea infusions was studied by size exclusion chromatography (SEC) and anion-exchange fast protein liquid
chromatography (FPLC). Fractions were collected throughout the chromatographic separations and Al was determined “off line”
by inductively coupled plasma optical emission spectroscopy (ICP–OES). Black, green, and red tea samples were investigated.
The total concentration of Al in tea infusions was determined by ICP–OES and ranged between 0.5 and 4 mg dm−3. The pH of tea infusions ranged between 5.3 and 5.5. Data from SEC–ICP–OES analysis indicated that 10–35% of total Al in
tea infusions was eluted at a retention volume corresponding to a molecular mass of approximately 3800 Da. The remaining Al
was adsorbed on the column resin. The same tea infusions were also analysed by anion-exchange FPLC–ICP–OES. It was found experimentally
that the same percentage of total Al as from the SEC column was eluted at a retention volume that corresponded to negatively
charged Al-citrate. The remaining Al was adsorbed on the column resin. Identification of Al-binding ligands eluting under
the chromatographic peak was performed by electrospray ionisation tandem mass spectrometry (ES–MS–MS) analysis. It was proven
that ionic Al species in tea infusions (10–35% of the total Al) corresponded to negatively charged Al-citrate. The remaining
species that was adsorbed on the SEC or FPLC columns was most probably bound to phenolic compounds. Speciation of Al in tea
with milk or lemon was also studied. Results for tea with milk indicated that Al-citrate was not transformed and that approximately
60% of total Al was transformed into high-molecular-mass Al species. This fraction was subjected to sodium dodecyl sulfonate
polyacryl gel electrophoresis (SDS–PAGE). The results indicated that Al was occluded by milk proteins (mostly caseins). When
citric acid was added to tea infusions the percentage of negatively charged Al-citrate remained either the same or increased
to 40% of total Al. 相似文献
14.
Nageswara Rao Anipindi 《Transition Metal Chemistry》2012,37(4):315-319
Bis(2,4,6-tripyridyl 1,3,5-triazine)iron(II),
\textFe(\textTPTZ) 2 2 + {\text{Fe(\text{TPTZ})}}_{ 2}^{{ 2 { + }}} reacts with 3-(2-pyridyl)-5,6-bis(4-phenyl-sulfonicacid)-1,2,4-triazine (PDTS) and 3-(4-(4-phenylsulfonicacid)-2-pyridyl)-5,6-bis(4-phenylsulfonic-acid)-1,2,4-triazine
(PPDTS) to give
\textFe(PDTS) 3 4- {\text{Fe(PDTS)}}_{ 3}^{ 4- } and
\textFe(PPDTS) 3 7- {\text{Fe(PPDTS)}}_{ 3}^{ 7- } respectively. Both of these substitution reactions are fast and their kinetics were monitored by stopped-flow spectrophotometry
in acetate buffers in the pH range of 3.6–5.6 at 25–45 °C. Both reactions are first order in
\textFe(TPTZ) 2 2 + {\text{Fe(TPTZ)}}_{ 2}^{{ 2 { + }}} and triazine, and pH has negligible effect on the rate. The kinetic data suggest that these reactions occur in an associative
path and a mechanism is proposed considering both protonated and unprotonated forms of PDTS and PPDTS are very similar in
reactivity. The kinetic and activation parameters have been evaluated. 相似文献
15.
The release of iron from ferritin by aceto- and benzohydroxamic acids was studied at two different iron chelator concentrations (100 and 10 mM), at two pH values (7.4 and 5.2), and in the presence or absence of urea. Collectively, the results demonstrate that both aceto- and benzohydroxamic acids remove iron from ferritin. Aceto- and benzohydroxamic acids penetrate the ferritin shell and react directly with the iron core of the ferritin cavity probably forming mono(hydroxamate) iron(III) complexes which exit ferritin and react with the excess hydroxamate in the solution to produce bis(hydroxamate) iron(III) complexes. The sizes of both the benzohydroxamic acid and the mono(benzohydroxamate) iron(III) complex, 6 and 7 A, respectively, are larger than that of the ferritin channels which indicates the flexibility of the channels to allow the entry and exit of these molecules. The size of the hydroxamic acid influenced the effectiveness of the iron release from ferritin following the expected trend with smaller iron chelators showing greater effectiveness. Likewise, the percentage of iron removed from ferritin was pH-dependent; the percentage of iron removed at pH 5.2 was greater than that at pH 7.4. Finally, the presence of urea, capable of opening the ferritin channels, dramatically increased the effectiveness of the iron chelator in removing iron from ferritin, especially at pH 7.4. 相似文献
16.
Antonio C. A. da Costa Fernanda N. do Corrêa Gustavo S. de Sant’Anna Gisele B. Tonietto José Marcus O. de Godoy Rodrigo A. de Gonçalves Márcia T. S. Lutterbach 《Chemical Papers》2016,70(5):602-609
The removal of non-reactive iron for different combinations of Fe2+ and tannic acid in irongall inks, via calcium phytate solutions, was studied. In parallel, the non-reactive iron removal kinetics was investigated using the pseudo first-order and second-order kinetic models. The results showed that the use of a dilute solution of calcium phytate to wash the impregnated paper strips removed the non-reactive iron from iron-gall inks in approximately 15 min in stoichiometric and non-stoichiometric combinations of iron and tannic acid. A second washing of the paper strips after an accelerated ageing, showed a distinct kinetic behaviour, with iron removal taking place simultaneously but apparently via a different mechanism. The use of a reference calcium phytate solution exhibited the same behaviour, suggesting that the use of dilute solutions as iron removal agents would represent less damage to historical documents. The results of kinetic modelling showed that all the combinations of Fe2+ and tannic acid used fitted the pseudo first-order kinetic model, when dilute and reference phytate solutions were tested as iron-desorbing agents. 相似文献
17.
A flow injection method for the sequential determination of iron(II) and iron(III) was developed. It is based on the differential
reaction kinetics of iron(II) and iron(III) with Tiron in a double-injection FI system. The proposed method employs the accelerating
action of copper(II) for the oxidation of iron(II) in the presence of Tiron. A linear calibration graph is obtained for iron
(II) and iron(III) in the concentration range 1.8 × 10–5– 1.8 × 10–4 mol/L; the throughput of samples is 30 injections/h.
Received: 22 October 1996 / Revised: 4 December 1996 / Accepted: 10 December 1996 相似文献
18.
Rodríguez-Fariñas N Gomez-Gomez MM Camara-Rica C 《Analytical and bioanalytical chemistry》2008,390(1):29-35
Oral administration of sodium tungstate is an effective treatment for type 1 and 2 diabetes in animal models; it does not
incur significant side effects, and it may constitute an alternative to insulin. However, the mechanism by which tungstate
exerts its observed metabolic effects in vivo is still not completely understood. In this work, serum-containing proteins
which bind tungstate have been characterized. Size exclusion chromatography (SEC) coupled to inductively coupled plasma mass
spectrometry (ICP-MS) with a Phenomenex Bio-Sep-S 2000 column and 20 mM HEPES and 150 mM NaCl at pH 7.4 as the mobile phase
was chosen as the most appropriate methodology to screen for tungsten–protein complexes. When human serum was incubated with
tungstate, three analytical peaks were observed, one related to tungstate–albumin binding, one to free tungstate, and one
to an unknown protein binding (MW higher than 300 kDa). Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF)
mass spectrometric analysis of the tungsten-containing fractions collected from SEC–ICP-MS chromatograms, after desalting
and preconcentration processes, confirmed the association of tungstate with albumin and the other unknown protein.
Figure SEC-ICP-MS // MALDI-TOF 相似文献
19.
The structure of glucofructans from Taraxacum officinale roots growing in Buryatia was studied by chemical, chromatographic, and spectral methods. It was found that fructose,glucose,
saccharose, 1-kestose, and nystose were present in the free state. The structures of the two dominant polymeric compounds,
TGf-1 (5.7 kDa) and TGf-2 (2.6 kDa), which were linear inulin-type macromolecules consisting of fructofuranose units bonded
through β-(2→1)-bonds, were studied.
Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 125–127, March–April, 2009. 相似文献
20.
B. Baraj J. L. Cortina A. Sastre M. Granados 《Fresenius' Journal of Analytical Chemistry》1998,360(2):263-265
The interference of copper on the spectrophotometric determination of iron with bathophenantroline-disulfonic acid disodium
salt was studied using an experimental design. Copper interferes even below pH 5 [1], forming a yellow complex with bathophenantroline
which turned to green after 5 min. This complex showed a maximum at 425 nm with a molar absorptivity of 7.5 × 103 L mol–1 cm–1. Microgram quantities of iron and copper were determined simultaneously in water standard samples using bathophenantroline-disulfonic
acid disodium salt at pH 4.8 and measuring the absorbances at two wavelengths. The interference of iron on the copper determination
was also estimated. The RSDs of the method for both Cu and Fe were below 1.7%. Recoveries for Cu and Fe were within the ranges
97.2% to 98% and 99.7 to 100.5%, respectively. The method was applied to the determination of copper and iron in the waste
water from a water treatment plant. The results obtained by spectrophotometry were compared with those obtained by flame AAS.
Received: 8 July 1996 / Revised: 2 June 1997 / Accepted: 6 June 1997 相似文献