共查询到17条相似文献,搜索用时 15 毫秒
1.
2.
粗碲是由铜、铅、锌冶炼带来的副产品,其中含有大量的金、银等贵金属。快速准确检测粗碲中银含量,具有十分重要的意义。样品预先采用硫酸溶解,还原沉淀金、银,过滤分离大部分的铋、硒、碲等元素,经配料、高温熔融,熔融态的金属铅捕集试料中的贵金属形成铅扣,试料的其他物质与熔剂生成易熔性熔渣。将铅扣灰吹,得金银合粒,清除合粒表面粘附的杂质,经硝酸分金,用硫氰酸钾滴定法测定银量。银的加标回收率在99.5%~101%,相对标准偏差(RSD)小于5%。方法速度快,稳定性好,适用于粗碲中银含量的测定。 相似文献
3.
4.
5.
Alexander P. Boichenko Vadim V. Markov Hoan Le Kong Anna G. Matveeva Lidia P. Loginova 《Central European Journal of Chemistry》2009,7(1):8-13
The dissociation constants of (4-amino-1-hydroxybutylidene)bisphosphonic (alendronic) acid, (3-(dimethylamino)-1-hydroxypropylidene)bisphosphonic
(olpadronic) acid and (3-amino-1-hydroxypropylidene)bisphosphonic (pamidronic) acid were obtained in aqueous solutions (0.10
M KCl) and micellar solutions of cetylpyridinium chloride (0.10 M CPC) at 25.0°C. With the exception of the third dissociation
constant of alendronic acid, the dissociation constants of alendronic, olpadronic and pamidronic acids in aqueous solutions
matched literature data. The possibility of sodium alendronate determination by acid-base titration by NaOH solution was theoretically
grounded on the basis of re-evaluated data of alendronic acid dissociation constants.
相似文献
6.
We propose a method for the determination of acid dissociation constants based on the rapid detection of the equivalence point (EP) by feedback-based flow ratiometry and the subsequent estimation of the half equivalence point (EP1/2). The titrant (e.g., NaOH) flow rate FB was varied in response to a control voltage Vc from a controller, while the titrand (e.g., CH3COOH) flow rate FA was held constant. The pH of the mixed solution was monitored downstream from the confluence point of the solutions following a knotted tubular mixer. Initially, Vc was increased linearly. At the instance the detector sensed EP, the ramp direction of Vc changed downward. The pH increased further because of the lag time between the mixing of solutions and the sensing of pH. Following the pH maximum, the pH decreased. The EP was sensed again in this downward scan. The Vc that gives EP1/2 was computed from the Vc just at the time of the EP detection. The Vc was held constant at this level for 18 s, and the plateau pH value thus obtained was taken to be the pKa of the analyte subject to activity corrections. Studies on the dependence of the pKa on the ionic strength or dielectric constant of the solution were conducted in an automated fashion by delivering NaCl solution or acetonitrile through an additional channel. Satisfactory results were obtained with good throughput (53 s per determination) and precision (R.S.D.≈0.3%) for various acids. 相似文献
7.
Ehala S Grishina AA Sheshenev AE Lyapkalo IM Kašička V 《Journal of chromatography. A》2010,1217(51):8048-8053
Thermodynamic acid-base dissociation (ionization) constants (pK(a)) of seven zwitterionic heterocyclic bases, first representatives of new heterocyclic family (2,3,5,7,8,9-hexahydro-1H-diimidazo[1,2-c:2',1'-f][1,3,2]diazaphosphinin-4-ium-5-olate 5-oxides), originally designed as chiral Lewis base catalysts for enantioselective reactions, were determined by capillary zone electrophoresis (CZE). The pK(a) values of the above very weak zwitterionic bases were determined from the dependence of their effective electrophoretic mobility on pH in strongly acidic background electrolytes (pH 0.85-2.80). Prior to pK(a) calculation by non-linear regression analysis, the CZE measured effective mobilities were corrected to reference temperature, 25°C, and constant ionic strength, 25 mM. Thermodynamic pK(a) values of the analyzed zwitterionic heterocyclic bases were found to be particularly low, in the range 0.04-0.32. Moreover, from the pH dependence of effective mobility of the bases, some other relevant characteristics, such as actual and absolute ionic mobilities and hydrodynamic radii of the acidic cationic forms of the bases were determined. 相似文献
8.
Summary Binding constants between the antibiotic ristocetin A (Rist A) and D-Ala-D-Ala terminus peptides were determined using affinity
capillary electrophoresis (ACE). In these experiments two techniques are used to obtain binding constants. In the first, a
plug of Rist A and non-interacting standards are injected and electrophoresed. Analysis of the change in the relative migration
time ratio (RMTR) of Rist, relative to the non-interacting standards, as a function of the concentration of peptide, yields a value for the
binding constant (Kb). In the second, samples of peptide and standards are injected and electrophoresed in increasing concentrations of Rist A
in the running buffer. Analysis using theRMTR yields aK
b. The findings described here demonstrate the advantage of using ACE for estimating binding parameters between antibiotics
and ligands. 相似文献
9.
Summary Capillary electrophoresis (CE) has proved to be a fast and convenient method for the determination of the dissociation constants
of non-UV absorbing solutes in the acidic pK
A range (2.0–2.5).
The electroosmotic flow was reversed by washing the capillary with 0.2% polybren aqueous solution. A series of background
electrolytes was prepared with phenylphosphonic acid (pK
A=1.29) and β-alanine (pK
A=3.55) with the same ionic strength and a high buffer capacity in order to improve the repeatability (0.1–0.2 %) of the electrophoretic
mobility and to determine the values of pK
A accurately.
This procedure was applied to the determination of the dissociation constants of several alkyl-alkylphosphonic acids whose
pK
A values have not yet been published in the literature. In this work, their dissociation constants have been found to vary
between 1.91 and 2.34 for alkyl-methylphosphonic acids and between 2.10 and 2.38 for alkyl-ethylphosphonic acids. 相似文献
10.
The mixed dissociation constants of four drug acids - losartan, paracetamol, phenylephrine and quinine - at various ionic strengths I of range 0.01 and 1.0 and at temperatures of 25 and 37 °C were determined using SPECFIT32 and SQUAD(84) regression analysis of the pH-spectrophotometric titration data. A proposed strategy of efficient experimentation in a dissociation constants determination, followed by a computational strategy for the chemical model with a dissociation constants determination, is presented on the protonation equilibria of losartan. Indices of precise methods predict the correct number of components, and even the presence of minor ones when the data quality is high and the instrumental error is known. Improved identification of the number of species uses the second or third derivative function for some indices, namely when the number of species in the mixture is higher than 3 and when, due to large variations in the indicator values even at logarithmic scale, the indicator curve does not reach an obvious point where the slope changes. The thermodynamic dissociation constant was estimated by nonlinear regression of {pKa, I} data at 25 and 37 °C: for losartan and 3.57(3), and 4.80(3), for paracetamol and 9.65(1), for phenylephrine and 8.95(1), and 10.22(1), for quinine and 4.12(1), and 8.46(2). Goodness-of-fit tests for various regression diagnostics enabled the reliability of the parameter estimates to be found. 相似文献
11.
Mixed dissociation constants of four drug acids, i.e. silychristin, silybinin, silydianin and mycophenolate at various ionic strengths I of range 0.01 and 0.30 and at temperatures of 25 and 37 °C were determined using the SQUAD(84) regression analysis program applied to pH-spectrophotometric titration data. The proposed strategy of an efficient experimentation in a protonation constants determination, followed by a computational strategy for the chemical model with a protonation constants determination, is presented on the protonation equilibria of silychristin. The thermodynamic dissociation constant pKaT was estimated by non-linear regression of {pKa, I} data at 25 and 37 °C: for silychristin pKa,1T=6.52(16) and 6.62(1), pKa,2T=7.22(13) and 7.41(5), pKa,3T=8.96(9) and 8.94(9), pKa,4T=10.17(7) and 10.03(8), pKa,5T=11.89(4) and 11.63(7); for silybin pKa,1T=7.00(4) and 6.86(5), pKa,2T=8.77(11) and 8.77(3), pKa,3T=9.57(8) and 9.62(1), pKa,4T=11.66(3) and 11.38(1); for silydianin pKa,1T=6.64(7) and 7.10(6), pKa,2T=7.78(5) and 8.93(1), pKa,3T=9.66(9) and 10.06(11), pKa,4T=10.71(7) and 10.77(7), pKa,5T=12.26(5) and 12.14(5); for mycophenolate pKaT=8.32(1) and 8.14(1). Goodness-of-fit tests for various regression diagnostics enabled the reliability of parameter estimates to be found. 相似文献
12.
The mixed dissociation constants of five drug acids—ambroxol, antazoline, naphazoline, oxymetazoline and ranitidine—at various ionic strengths I of range 0.01 and 1.0 and at temperatures of 25 and 37 °C were determined using SQUAD(84) regression analysis of the pH-spectrophotometric titration data. A proposed strategy of efficient experimentation in a protonation constants determination, followed by a computational strategy for the chemical model with a protonation constants determination, is presented on the protonation equilibria of ambroxol. The thermodynamic dissociation constant pKaT was estimated by non-linear regression of {pKa, I} data at 25 and 37 °C: for ambroxol and 8.25 (4), log and 11.83 (8), for antazoline and 7.83 (6), and 9.55 (2), for naphazoline and 10.63 (1), for oxymethazoline and 10.77 (7), pKa,2T=12.03(3) and 11.82 (4) and for ranitidine and 1.77 (1). Goodness-of-fit tests for various regression diagnostics enabled the reliability of the parameter estimates to be found. 相似文献
13.
Rudnev AV Aleksenko SS Semenova O Hartinger CG Timerbaev AR Keppler BK 《Journal of separation science》2005,28(2):121-127
A CE method has been developed to evidence and quantitatively characterize the interaction between platinum-based antitumor drugs and human serum proteins. This method is a variant of affinity CE modified regarding both experimental setup and data treatment so as to measure the peaks (or vacancies) that correspond to the bound drug when it slowly binds to the protein. Using the formalism of the Hummel-Dreyer method and cisplatin and oxaliplatin as test compounds, a protocol for determining albumin and transferrin binding constants and stoichiometries, including (and distinguished by) 48 hours of incubation of the reaction mixture, was elaborated. Relative affinities of drugs toward different proteins in aqueous solution at physiological pH, chloride concentration, and temperature were compared in terms of overall binding constants and numbers of drug molecules attached to the protein. The results indicate that both platinum drugs bind to albumin more strongly than to transferrin, supporting the concept that the albumin fraction is a major drug supply route for chemotherapeutical needs. From a comparison with the binding parameters measured previously for cisplatin by other methods, conclusions were drawn about the validity of CE as a simple and convenient method for assaying protein-drug reactions with slow kinetics. 相似文献
14.
Petra Sázelová Dušan Koval Lukáš Severa Filip Teplý Gyula Vigh Václav Kašička 《Electrophoresis》2020,41(7-8):523-535
In this study, the apparent binding constants and limiting mobilities of the multiply charged complexes of the Δ− and Λ−enantiomers of Ru(II)- and Fe(II)-polypyridyl associates ([Ru(2,2′-bipyridine)3]2+, [Ru(1,10-phenanthroline)3]2+, and [Fe(1,10-phenanthroline)3]2+) with single-isomer 2,3-diacetylated-6-sulfated-cyclodextrins (CDs) (12Ac-6S-α-CD, 14Ac-7S-β-CD, and 16Ac-8S-γ-CD) were determined by ACE using uncorrected and ionic strength corrected actual mobilities of the species involved. Two limiting models were tested for the ionic strength correction of the actual mobilities based on an empirical relation for the ionic strength correction of multivalent ionic species. In model 1, the nominal values of the charge numbers (zS,nom) and analytical concentrations (cS,nom) of the above CD selectors in the BGEs were applied for calculation of the BGE ionic strength, as usual. In model 2, the CD selectors were considered as singly charged species (zS = −1) with |zS,nom|-times higher concentrations in the BGE than their analytical concentrations (cS = |zS,nom| × cS,nom) in the calculation of the BGE ionic strength. In all three cases–with uncorrected actual mobilities as well as with actual mobilities corrected according to the two limiting models–the measured effective mobilities of the above enantiomers fit well the theoretical curves of their mobility dependences on the CD selectors concentrations in the BGE, with high average coefficients of determination (R2 = 0.9890–0.9995). Nevertheless, the best physico-chemically meaningful values of the apparent binding constants and the limiting mobilities of the enantiomer-CDs complexes with low RSDs were obtained using the actual mobilities of the species involved corrected according to model 2. 相似文献
15.
Rank annihilation factor analysis (RAFA) is applied to resolve the two-way kinetic-spectral data measured from spectroscopic reactions and acquire rate constants and the absorption spectrum of each component. A two-step first-order consecutive reaction is studied in this paper. When the first step rate constant acts as an optimizing object, and simply combined with the pure spectrum of reactant, the rank of the original data matrix can be reduced by one by annihilating the information of reactant from the original data matrix. The residual standard deviation (R.S.D.) of the residual matrix after bilineaization of the background matrix is regarded as the evaluation function. Owing to the correlation between kinetic functions of species in the reaction, two optimal resolutions, corresponding to the rate constants of the first and second step, respectively, can both be obtained in one computing process. Given the kinetic parameters, the absorption spectrum of each component including the intermediate can be obtained through least square regression. This approach can also be applied to reaction systems where the intermediate or the final product doesnot absorb. The performance of the method has been evaluated by using synthetic data. Electrodegradation of phenol solution and alkaline hydrolysis of dimethyl phthalate were also studied by the present method. 相似文献
16.
The mixed dissociation constants of four anticancer drugs - camptothecine, 7-ethyl-10-hydroxycamptothecine, 10-hydroxycamptothecine and 7-ethylcamptothecine, including diprotic and triprotic molecules at various ionic strengths I of range 0.01 and 0.4, and at temperatures of 25 and 37 °C - were determined with the use of two different multiwavelength and multivariate treatments of spectral data, SPECFIT32 and SQUAD(84) nonlinear regression analyses and INDICES factor analysis. A proposed strategy for dissociation constants determination is presented on the acid-base equilibria of camptothecine. Indices of precise modifications of the factor analysis in the program INDICES predict the correct number of components, and even the presence of minor ones, when the data quality is high and the instrumental error is known. The thermodynamic dissociation constant was estimated by nonlinear regression of {pKa, I} data at 25 and 37 °C: for camptothecine and 3.02(8), and 10.23(8); for 7-ethyl-10-hydroxycamptothecine, and 2.46(6), and 8.74(3), and 9.47(8); for 10-hydroxycamptothecine and 2.84(5), and 8.92(2), and 9.98(4); and for 7-ethylcamptothecine and 3.30(16), and 10.98(18). Goodness-of-fit tests for various regression diagnostics enabled the reliability of the parameter estimates found to be proven. Pallas and Marvin predict pKa being based on the structural formulae of drug compounds in agreement with the experimental value. 相似文献
17.
《Journal of separation science》2017,40(10):2214-2227
Algae can synthesize, accumulate and store large amounts of lipids in its cells, which holds immense potential as a renewable source of biodiesel. In this work, we have developed and validated a GC–MS method for quantitation of fatty acids and glycerolipids in forms of fatty acid methyl esters derived from algae biomass. Algae Scenedesmus dimorphus dry mass was pulverized by mortar and pestle, then extracted by the modified Folch method and fractionated into free fatty acids and glycerolipids on aminopropyl solid‐phase extraction cartridges. Fatty acid methyl esters were produced by an optimized one‐step esterification of fatty acids and transesterification of glycerolipids with boron trichloride/methanol. The matrix effect, recoveries and stability of fatty acids and glycerolipids in algal matrix were first evaluated by spiking stable isotopes of pentadecanoic‐2,2‐d2 acid and glyceryl tri(hexadecanoate‐2,2‐d2) as surrogate analytes and tridecanoic‐2,2‐d2 acid as internal standard into algal matrix prior to sample extraction. Later, the method was validated in terms of lower limits of quantitation, linear calibration ranges, intra‐ and inter‐assay precision and accuracy using tridecanoic‐2,2‐d2 acid as internal standard. The method developed has been applied to the quantitation of fatty acid methyl esters from free fatty acid and glycerolipid fractions of algae Scenedesmus dimorphus . 相似文献