共查询到20条相似文献,搜索用时 31 毫秒
1.
Paula Messina Marcela A. Morini Pablo C. Schulz Gerardo Ferrat 《Colloid and polymer science》2002,280(4):328-335
We used a battery of different methods to study the association in aqueous sodium dehydrocholate (NaDHC) solutions. This
salt associates by a stepwise mechanism. Below (9.6 ± 4.2) × 10−4 mol dm−3 there is a molecular solution with some strongly insoluble dehydrocholic acid produced by hydrolysis. Between (9.6 ± 4.2) × 10−4 and (5.2 ± 2.2) × 10−3 mol dm−3, an aggregate similar to acid soap (NaDHC.HDHC) appears and its amount and the aggregate's size increase with concentration.
At =(2.20 ± 0.85) × 10−2 mol dm−3 the aggregates formed have properties usually associated with true micelles, such as solubilisation of water-insoluble dyes.
These aggregates increase in size with concentration and change their shape at 8 × 10−2 mol dm−3, giving nonsymmetrical aggregates. The changes in the solution physicochemical properties at these concentrations may be
misinterpreted and this explains the different values of the critical micelle concentration reported in the literature for
substances with similar structure, such as bile salts.
Received: 14 May 2001 Accepted: 10 August 2001 相似文献
2.
The aim of this study was to compare the adsorption of various organic drugs and a well-studied surfactant. The organic drugs
used were promethazine chloride [10-(2-dimethylammonium) propylfenothiazine chloride] and buformin hydrochloride (1-butylbiguanidine
chloride). The surfactant was benzalkonium chloride (N-tridecyl-N-benzyl-N,N-dimethylammonium chloride). Different amounts of drug solutions were added to montmorillonite suspensions, either separately
(simple system) or in combination (competitive system) under the same conditions, and the organocomplexes formed were investigated.
The organic molecule with the short alkyl chain adsorbed to yield monolayer coverage, whereas the aromatic molecule and the
surfactant formed a pseudotrimolecular arrangement. In the competitive system, the larger organic molecules (having the same
charge) displaced the smaller one from the interlayer space. The intercalation of molecules in the interlayer space was investigated
by X-ray diffraction measurements.
Received: 30 November 2000 Revised: 20 December 2001 Accepted: 26 October 2001 相似文献
3.
Fathalla Belal Saadia M. El-Ashry Ihsan M. Shehata Magda A. El-Sherbeny Dina T. El-Sherbeny 《Mikrochimica acta》2000,135(3-4):147-154
A highly sensitive differential-pulse (DPP) polarographic method is described for the determination of three N-substituted
phenothiazine derivatives, chlorpromazine (CZ), promazine (PZ) and promethazine (PMZ). The method involves the use of nitrous
acid as an oxidant. Polarographically-active sulphoxides with diffusion-current constants (Id) of 2.53, 3.05 and 3.37 were
obtained for CZ, PZ and PMZ, respectively. The polarographic waves were characterized as being diffusion-controlled, irreversible
and partly affected by adsorption phenomena. All parameters affecting the oxidation process and polarographic behaviour were
optimized and incorporated into the procedure. The limiting current-concentration plots in the DPP mode were rectilinear over
the range: 0.006–0.1 mM, 0.005–0.08 mM and 0.008–0.1 mM for CZ, PZ and PMZ, respectively, with minimum detectability (S/N=3)
of 3 × 10−7 M for CZ and PZ, and 4 × 10−7 M for PMZ, respectively. The kinetic parameters of the electrode reaction, including rate constant, free energy of activation
ΔG and effect of temperature on both parameters were studied. The proposed method was successfully applied to the determination
of phenothiazines in dosage forms; the results obtained were in agreement with those given with the official methods. The
method was further applied to the determination of promazine in spiked human urine. The percentage recovery was 96.86 ± 0.30.
The advantages of the proposed method over other reported methods were discussed. A proposal of the electrode reaction was
made.
Received June 1, 1999. Revision March 10, 2000. 相似文献
4.
Lottmann A Cadé E Geagea ML Delhomme O Grand C Veilleraud C Rizet AL Mirabel P Millet M 《Analytical and bioanalytical chemistry》2007,387(5):1855-1861
In to order increase sensitivity and to reduce the background induced by matrix effects, a method was developed that uses
flash chromatography to separate various compounds present in atmospheric aerosol samples prior to their analysis with different
analytical techniques (GC–MS, GC–FID, HPLC). For this purpose, flash chromatography using a 4 g silica gel column crossed
by eluent at a flow rate of 20 mL min−1 was used. An eluent with enhanced polarity is needed to separate nonpolar (linear and branched alkanes), semipolar (PAH,
nitro-PAH and cholesterol) and polar (methoxyphenols, alkanoic acids, and levoglucosan) compounds. Three combinations of solvents
were used: hexane for the nonpolar fraction (F1), toluene/hexane for the semipolar fraction (F2) and dimethylformamide for
the polar fraction (F3). The use of different eluents for each fraction allows separation of the sample to be accomplished
with good repeatability and satisfying yields [85 ± 5% for F1, 81 ± 8% (PAHs), 89 ± 6% (nitro-PAHs) and 74 ± 7% (cholesterol)
for F2 and 79 ± 7% (n-alkanoic acids), 40 ± 11% (methoxyphenols) and 77 ± 6% (levoglucosan) for F3]. The methoxyphenol yields were low due to losses
during the concentration/evaporation step. This method was then applied to analyse the organic composition of particles collected
at an urban site in Strasbourg (France). 相似文献
5.
Krska R Schubert-Ullrich P Josephs RD Emteborg H Buttinger G Pettersson H van Egmond HP Schothorst RC Macdonald S Chan D 《Analytical and bioanalytical chemistry》2007,388(5-6):1215-1226
This paper presents results from the European Commission-funded project Doncalibrant, the objective of which was to produce
calibrators with certified mass fractions of the Fusarium toxins deoxynivalenol (DON), 3-acetyldeoxynivalenol (3-Ac-DON), 15-acetyldeoxynivalenol (15-Ac-DON), and nivalenol (NIV),
in acetonitrile. The calibrators, available in ampoules, were sufficiently homogeneous, with between-bottle variations (s
bb) of less than 2%. Long-term stability studies performed at four different temperatures between −18 and 40 °C revealed no
significant negative trends (at a confidence level of 95%). Molar absorptivity coefficients (in L mol−1 cm−1) were determined for all four toxins (DON: 6805 ± 126, NIV: 6955 ± 205, 3-Ac-DON: 6983 ± 141, 15-Ac-DON: 6935 ± 142) on the
basis of a mini-interlaboratory exercise. The overall uncertainty of the calibrators’ target values for DON and NIV were evaluated
on the basis of gravimetric preparation data and include uncertainty contributions from possible heterogeneity, storage, and
transport. The Doncalibrant project resulted in the production of calibrators for DON (IRMM-315) and NIV (IRMM-316) in acetonitrile
with certified mass fractions of 25.1 ± 1.2 μg g−1 and 24.0 ± 1.1 μg g−1, respectively. Both CRMs became commercially available from the Institute for Reference Materials and Measurements (IRMM,
Geel, Belgium) at the beginning of 2007. 相似文献
6.
Issa Yavari Mehdi Adib Hamid R. Bijanzadeh Majid M. M. Sadegi Hossein Logmani-Khouzani Javad Safari 《Monatshefte für Chemie / Chemical Monthly》2002,133(8):1109-1113
Summary. A dynamic NMR effect is observed in the 13C NMR spectra of anhydrous quinophthalone (quinoline yellow) and its monohydrate in the vicinity of 47°C and 0°C, respectively,
and is attributed to a restricted rotation around the polarized carbon–carbon double bond. The free energy of activation for
this process in anhydrous quinophthalone and the monohydrate is 65±2 and 55±2 kJ · mol−1, respectively, in CDCl3.
Received September 25, 2001. Accepted (revised) November 14, 2001 相似文献
7.
M. Soledad García Joaquín Ortuño M. Isabel Albero María Cuartero 《Analytical and bioanalytical chemistry》2009,394(6):1563-1567
A trazodone-selective electrode for application in pharmaceutical quality control and urine analysis was developed. The electrode
is based on incorporation of a trazodone-tetraphenylborate ion exchanger in a poly(vinyl chloride) membrane. The electrode
showed a fast, stable and Nernstian response over a wide trazodone concentration range (5 × 10−5−1 × 10−2 M) with a mean slope of 59.3 ± 0.9 mV/dec of concentration, a mean detection limit of 1.8 × 10−5 ± 2.2 × 10−6 M, a wide working pH range (5–7.5) and a fast response time (less than 20 s). The electrode also showed good accuracy, repeatability,
reproducibility and selectivity with respect to some inorganic and organic compounds, including the main trazodone metabolite.
The electrode provided good analytical results in the determination of trazodone in pharmaceuticals and spiked urine samples;
no extraction steps were necessary. Dissolution testing of trazodone tablets, in different conditions of pH and particle size,
based on a direct potentiometric determination with the new selective electrode is presented as well. 相似文献
8.
T. Hellweg C. D. Dewhurst E. Brückner K. Kratz W. Eimer 《Colloid and polymer science》2000,278(10):972-978
Poly (N-isopropylacrylamide) microgel particles are found to form colloidal crystals similar to those occurring in typical hard-sphere
colloids like poly(methylmethacrylate) beads. Samples made of particles with different cross-linker concentrations are investigated
and their deswelling ratio is determined using dynamic light scattering. Small-angle neutron scattering data are also presented
and analysed in terms of a face-centred-cubic crystal structure. The characteristic length, a, of the elementary cell is found to be 535 ± 16 and 495 ± 15 nm for the two systems investigated. This leads to particle
radii of 189 ± 6 and 175 ± 5 nm, respectively. These values compare well to the radii determined using several different methods.
Received: 26 July 1999/Accepted: 21 March 2000 相似文献
9.
The Effect of pH on Continuous Biohydrogen Production from Swine Wastewater Supplemented with Glucose 总被引:1,自引:0,他引:1
Yecong Li Jun Zhu Xiao Wu Curtis Miller Liang Wang 《Applied biochemistry and biotechnology》2010,162(5):1286-1296
The effect of pH on hydrogen production from liquid swine manure supplemented with glucose by a mixed culture of fermentative
bacteria in an anaerobic sequencing batch reactor was evaluated in this study. At 37 ± 1 °C, five pH values ranging from 4.7
to 5.9 at an increment of 0.3 were tested at a hydraulic retention time (HRT) of 16 h. The results showed that at this HRT,
the optimal pH for hydrogen production was 5.0, under which the biogas comprised 33.57 ± 5.65% of hydrogen with a production
rate of 8.88 ± 2.94 L-H2/day and a yield of 1.48 ± 0.49 L-H2/L liquid swine manure. The highest biomass concentration, highest butyric acid to acetic acid ratio, lowest propionic acid
concentration, and the best stability were all found at pH 5.0, while the highest CH4 productivity was found at pH 5.9. For efficient hydrogen production, oxygen content should be controlled under 2%, beyond
which an inverse linear relationship (R
2 = 0.986) was observed. 相似文献
10.
Submicron-sized, comparatively monodisperse poly (methyl methacrylate) particles were produced by dispersion polymerization
of methyl methacrylate with a poly(dimethylsiloxane)-based azoinitiator in supercritical carbon dioxide at 30 MPa for 24 h
at 65 °C. The initiator operated not only as a radical initiator but also as a colloidal stabilizer, and was named an “inistab”.
Received: 13 February 2001 Accepted: 20 June 2001 相似文献
11.
The redox characteristics of the drug domperidone at a glassy-carbon electrode (GCE) in aqueous media were critically investigated
by differential-pulse voltammetry (DPV) and cyclic voltammetry (CV). In Britton–Robinson (BR) buffer of pH 2.6–10.3, an irreversible
and diffusion-controlled oxidation wave was developed. The dependence of the CV response of the developed anodic peak on the
sweep rate (ν) and on depolizer concentration was typical of an electrode-coupled chemical reaction mechanism (EC) in which an irreversible
first-order reaction is interposed between the charges. The values of the electron-transfer coefficient (α) involved in the rate-determining step calculated from the linear plots of E
p,a against ln (ν) in the pH range investigated were in the range 0.64 ± 0.05 confirming the irreversible nature of the oxidation peak. In
BR buffer of pH 7.6–8.4, a well defined oxidation wave was developed and the plot of peak current height of the DPV against
domperidone concentration at this peak potential was linear in the range 5.20 × 10−6 to 2.40 × 10−5 mol L−1 with lower limits of detection (LOD) and quantitation (LOQ) of 6.1 × 10−7 and 9.1 × 10−7 mol L−1, respectively. A relative standard deviation of 2.39% (n = 5) was obtained for 8.5 × 10−6 mol L−1 of the drug. These DPV procedures were successfully used for analysis of domperidone in the pure form (98.2 ± 3.1%), dosage
form (98.35 ± 2.9%), and in tap (97.0 ± 3.6%) and wastewater (95.0 ± 2.9%) samples. The method was validated by comparison
with standard titrimetric and HPLC methods. Acceptable error of less than 3.3 % was also achieved.
Figure In aqueous media at pH 7.6- 8.4, the DPV and cyclic voltammetry of the drug domperidone (I) at GCE showed an irreversible
and diffusion controlled oxidation wave. The values of the electron transfer coefficient (α) involved in the rate determining
step were found in the range 0.64± 0.05 confirming the irreversible nature of the peak. The analysis of the drug in pure form
and in wastewater samples was successfully achieved 相似文献
12.
Othman AM El-Houseini ME El-Sofy MS Aboul-Enein HY 《Analytical and bioanalytical chemistry》2011,400(3):787-795
The activity of the α-l-fucosidase (AFU) enzyme represents an excellent test for diagnosis of hepatocellular carcinoma (HCC) and fucosidosis recognized
in inborn disorder of metabolism and increases the sensitivity of detection to 95.5% in patients with HCC. Therefore, the
determination of the activity of AFU enzyme is very important and can be used as a screening tool for the early diagnosis
of tumors for HCC patients. A simple, accurate, and sensitive potentiometric method was developed for measuring the activity
of AFU. The method was based upon measuring the concentration of 2-chloro-4-nitrophenol (2-chloro-4-NP) using a 2-chloro-4-NP-rhodamine
B ion pair in a PVC membrane sensor. The electrode shows a linear, reproducible, and stable potentiometric response with an
anionic Nernstian slope of −51.13 ± 0.6 mV/decade over a wide range of concentrations 10−5–10−2 M and a detection limit of 1.0 × 10−6 M of 2-chloro-4-NP. The membrane exhibits a fast response time of 30 s, over a pH range of 4.0–6.5. The selectivity coefficients
indicate excellent selectivity for 2-chloro-4-NP over a number of interfering species, e.g., chloride, nitrate, sulfate, chromate
urea, albumin, glucose, uric acid, and total protein. The prepared sensor has been used successfully for the determination
of 2-chloro-4-NP produced from the hydrolysis of 2-chloro-4-NP-α-l-fucopyranoside substrate. It was also applied for the determination α-l-fucosidase enzyme of 33 serum samples of healthy subjects and patients. The average recoveries ± RSD for the healthy subjects,
cirrhosis of chronic hepatitis C and B, and HCC serum samples were 102.6 ± 1.01%, 101.5 ± 0.95%, and 100.1 ± 1.1%, respectively.
The results obtained are in good agreement with those obtained by standard methods. 相似文献
13.
We studied the adsorption of two neutral polymers [poly(vinyl pyrrolidone) and poly(vinyl alcohol) (PVA)] on negatively charged
liposomes composed of 25:2:3 (molar ratio) soy lecithin/dicetyl phosphate/cholesterol.The liposomes were prepared in buffered
solution at pH 7.4 and were mixed with the solution of the polymers in the desired polymer/lipid ratios. Adsorption was measured
by determination of the equilibrium bulk concentration of the polymer. Protamine hydrochloride was used to aggregate the liposomes
with polymers adsorbed on their surface and to facilitate their separation from the equilibrium bulk solution. In the case
of PVA, quantitative adsorption measurements with a specific reagent were possible. Adsorption isotherms were recorded at
25 ± 0.2 °C. It was concluded that adsorbed and nonadsorbed PVA molecules are in equilibrium even at low polymer/lipide ratios.
The results were confirmed by dynamic laser light scattering, X-ray diffraction and thermal activity monitoring experiments.
Received: 13 October 2000 Accepted: 8 March 2001 相似文献
14.
M. Ocaña 《Colloid and polymer science》2002,280(3):274-281
A procedure to prepare submicrometre spherical particles of Pr(III), Ce(III) or Pr(III)-doped C(III) hydroxycarbonates with
narrow size distribution is reported. The particles were obtained by aging aqueous solutions of Pr(III) chloride and/or Ce(III)
nitrate in the presence of urea at 100 °C for 2 h. The effect of Pr and/or Ce salt concentrations in the starting solutions
on the size, shape and composition of the precipitated particles is reported. The thermal behaviour of the basic carbonates
up to decomposition into the metal oxides was followed by differential thermal and thermogravimetric analyses, X-ray diffraction,
IR spectroscopy and transmission electron microscopy. All the systems were also characterized by their electrokinetic behaviour
(determination of isoelectric point) and specific surface areas. The colour of the powders was also evaluated as a function
of the Pr content and temperature and was compared with previous results on red pigments of similar composition.
Received: 30 May 2001 Revised: 17 September 2001 Accepted: 20 September 2001 相似文献
15.
A potentiometric azide-selective sensor based on the use of iron(III) hydrotris(3,5-dimethylpyrazolyl)borate acetylacetonate
chloride [TpMe2Fe(acac)Cl] as a neutral carrier for an azide-selective electrode is reported. Effect of various plasticizers, viz. o-nitrophenyloctyl ether (o-NPOE), dioctylphthalate (DOP), dibutylphthalate (DBP), and benzylacetate (BA), and an anion excluder, hexadecyltrimethylammonium
bromide (HTAB), with [TpMe2Fe(acac)Cl] complex in poly(vinyl chloride) (PVC) were studied. The best performance was obtained with a membrane composition
of [TpMe2Fe(acac)Cl]/HTAB/DOP/PVC in a ratio of 5:2:190:100 (w/w). The sensor exhibits significantly enhanced selectivity toward azide
ions over the concentration range 6.3 × 10−7 to 1.0 × 10−2 M with a lower detection limit of 3.8 × 10–7 M and a Nernstian slope of 59.4 ± 1.1 mV decade−1. Influences of the membrane composition, pH and possible interfering anions were investigated on the response properties
of the electrode. Fast and stable response, good reproducibility, long-term stability and applicability over a wide pH range
(3.5–9.0) are demonstrated. The sensor has a response time of 14 s and can be used for at least 45 days without any considerable
divergence in the potential response. The proposed electrode shows fairly good discrimination of azide from several inorganic
and organic anions. It was successfully applied to the direct determination of azide in orange juice, tea extracts and human
urine samples. 相似文献
16.
The alterations of organic acids citrate, α-ketoglutarate, succinate, fumarate, malate production together with isocitrate
lyase activity as a glyoxalate shunt enzyme, and antibiotic production of Streptomyces sp M4018 were investigated in relation to changes in the glucose, glycerol and starch concentrations (5–20 g/L) after identification
as a strain of Streptomyces hiroshimensis based on phenotypic and genotypic characteristics. The highest intracellular citrate and α-ketoglutarate levels in 20 g/l
of glucose, glycerol, and starch mediums were 399.47 ± 4.78, 426.93 ± 6.40, 355.84 ± 5.38 ppm and 444.81 ± 5.12, 192.96 ± 2.26,
115.20 ± 2.87 ppm, respectively. The highest succinate, malate, and fumarate levels were also determined in 20 g/l of glucose
medium as 548.9 ± 11.21, 596.15 ± 8.26, and 406.42 ± 6.59 ppm and the levels were significantly higher than the levels in
glycerol and starch. Extracellular organic acid levels measured also showed significant correlation with carbon source concentrations
by showing negative correlation with pH levels of the growth medium. The antibiotic production of Streptomyces sp. M4018 was also higher in glucose medium as was the case also for organic acids when compared with glycerol. On the other
hand, there is no production in starch. 相似文献
17.
Naracham Veedu Sreekumar Ronald Aquin Nazareth Badiadka Narayana Prashant Hegde Busnur Rachotappa Manjunatha 《Mikrochimica acta》2002,140(1-2):63-67
A complexometric method for the determination of mercury in presence of other metal ions based on the selective masking ability
of potassium bromide towards mercury is described. Mercury(II) present in a given sample solution is first complexed with
a known excess of EDTA and the surplus EDTA is titrated against zinc sulfate solution at pH 5–6 using xylenol orange as the
indicator. A known excess of 10% solution of potassium bromide is then added and the EDTA released from Hg-EDTA complex is
titrated against standard zinc sulfate solution. Reproducible and accurate results are obtained for 8 mg to 250 mg of mercury(II)
with a relative error ± 0.28% and standard deviations ≤0.5 mg. The interference of various ions is studied. This method was
applied to the determination of mercury(II) in its alloys.
Received April 18, 2001 Revision October 10, 2001 相似文献
18.
Takashi Masadome 《Mikrochimica acta》2002,140(3-4):227-231
A cationic surfactant-selective electrode for sensitive analysis of cationic surfactants has been developed by using a plasticized
poly (vinyl chloride) membrane based on a hydrophobic cation exchanger, sodium tetrakis (3,5-bis(trifluoromethyl)phenyl) borate.
The electrode shows a Nernstian response to dodecyltrimethylammonium (DTA) ion in the concentration range from 8 × 10−7 M to 10−2 M with a slope of 55.3 ± 2.0 mV/decade. The electrode was used over a wide pH range of pH 2–12. The electrode is excellently
selective for the DTA ion over inorganic anions, but interferences of other cationic surfactants such as cetylpyridinium ion
and tetradecyldimethylbenzylammonium ion (zephiramine) are great.
The present electrode was applied to determine total cationic surfactants in commercial disinfectants.
Received February 27, 2002; accepted June 14, 2002 相似文献
19.
Sayed S. Badawy Yousry M. Issa Waheed F. El-Hawary Manal S. Ashour 《Mikrochimica acta》2001,136(1-2):1-7
A PVC membrane electrode selective for cetyldimethylethylammonium (CDEA) ion was prepared. The active element is a plasticized
poly vinyl chloride membrane containing a dissolved ion associate complex of CDEA with phosphotungstic acid (PTA). The electrode
showed a near-Nernstian response within the CDEA+ concentration range 2.34 × 10−6 to 1.96 × 10−4 M at 25 ± 1^C, good selectivity, and is usable within the pH range 3.5–9.0. The isothermal temperature coefficient of the electrode amounted
to −0.00012 V/°C. The electrode has been used for the direct determination of cetyldimethylethylammonium bromide either by
the standard addition method or by potentiometric titration against PTA.
Received January 1, 1998. Revision June 13, 2000. 相似文献
20.
Joaquin F. Perez-Benito 《Monatshefte für Chemie / Chemical Monthly》2001,132(12):1477-1492
Summary. The catalytic action of Cu(II) on the decomposition of H2O2 in near-neutrality aqueous solutions is activated by halide ions. The activation energies amount to 113±7 (parent reaction)
and 69.9±1.4 (chloride-activated reaction) kJ · mol−1. Free-radical chain mechanisms are proposed for both the parent reaction and the halide-activated reaction. The catalyst
activation caused by halide ions is explained in terms of coordination of halide ligands by both Cu(II) and Cu(I), the coordination
causing a higher stabilization of Cu(I) than of Cu(II). At low concentrations, Br− causes an inhibition of the Cu(II)/H2O2 reaction. This is explained in terms of an increase of the rate of termination of the chain reaction due to the scavenging
effect of OH radicals caused by Br−.
Received March 27, 2001. Accepted (revised) May 25, 2001. 相似文献