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1.
A set of 25 monoprotic bases is proposed as internal standards for pK(a) determination by capillary electrophoresis. The pK(a) of the bases is determined and compared with available literature data. The capillary electrophoresis internal standard method offers numerous advantages over other typical methods for pK(a) determination, especially of analysis time and buffer preparation. However, it requires disposing of appropriate standards with reference pK(a) value. The set of bases established in this work together with the set of acids previously established provide a reference set of compounds with well-determined acidity constants that facilitate the process of selecting appropriate internal standards for fast pK(a) determination by capillary electrophoresis in high throughput screening of pharmaceutical drugs. In addition, the performance of the method when acidic internal standards are used for the determination of acidity constants of basic internal standards has also been tested. Although higher errors may be expected in this case, good agreement is observed between determined and literature values. These results indicate that in most cases structural similarity between the analyte and the internal standard might not be an essential requirement in the internal standard method. 相似文献
2.
Elisabet Fuguet Clara RàfolsElisabeth Bosch Martí Rosés 《Journal of chromatography. A》2009,1216(17):3646-3651
A new and fast method to determine acidity constants of monoprotic weak acids and bases by capillary zone electrophoresis based on the use of an internal standard (compound of similar nature and acidity constant as the analyte) has been developed. This method requires only two electrophoretic runs for the determination of an acidity constant: a first one at a pH where both analyte and internal standard are totally ionized, and a second one at another pH where both are partially ionized. Furthermore, the method is not pH dependent, so an accurate measure of the pH of the buffer solutions is not needed. The acidity constants of several phenols and amines have been measured using internal standards of known pKa, obtaining a mean deviation of 0.05 pH units compared to the literature values. 相似文献
3.
Research on the structure–activity relationships of molecules with acidic carbon atoms led us to undertake a feasibility study on the determination of their acidity constants by capillary electrophoresis (CE). The studied molecules had diverse structures and were tetronic acid, acetylacetone, diethylmalonate, Meldrums acid, 3-methylrhodanine, nitroacetic acid ethyl ester, pyrimidine-2,4,6-trione, 3-oxo-3-phenylpropionic acid ethyl ester, 1-phenylbutan-1,3-dione, 5,5-dimethylcyclohexan-1,3-dione and homophthalic anhydride. The pKa range explored by CE was therefore very large (from 3 to 12) and pKa values near 12 were evaluated by mathematical extrapolations. The analyses were carried out in CZE mode using a fused silica capillary grafted (or not) with hexadimethrine. Owing to the electrophoretic behaviour of these compounds according to the pH, their acidity constants could be evaluated and appeared in perfect agreement with the literature data obtained, a few decades ago, by means of potentiometry, spectrometry or conductimetry. The pKa of homophthalic anhydride and 3-methylrhodanine were evaluated for the first time. 相似文献
4.
The internal standard (IS) CE (IS‐CE) method is an interesting alternative to other methods for the determination of acidity constants of compounds. Although some of the advantages of this method have been already reported, the method has not been tested yet as regards to temperature effects. This has been the aim of this work, where it is demonstrated that the method can be applied successfully for the determination of pKas at different temperatures, if the acidity constant of the IS at the desired temperature is known. The fact of obtaining the acidity constants at different temperatures allows the calculation of some thermodynamic quantities, such as the molar standard enthalpy and the molar standard entropy in a fast way. It is also demonstrated that if the IS and the test compound have similar standard enthalpy increment, the IS compensates uncontrolled possible temperature fluctuations (e.g., due to Joule heat) inside the capillary obtaining reliable acidity constant values at the desired temperature. 相似文献
5.
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
6.
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
7.
A fast capillary zone electrophoresis (CZE) method has been developed for the determination of four flavonoids (liquiritin, licoisoflavone A, licochalconel A and calycosin) in Glycyrrhizae radix. After a series of optimization experiments, 100 mM borate buffer (pH 10.5), 30 kV applied voltage and 35 °C temperature were selected. The contents of four flavonoids in cultivated and wild crude drugs of Glycyrrhizae radix with different growth periods from one to four years, collected from different areas were successfully determined within 8 min, with satisfactory repeatability and recovery. 相似文献
8.
A capillary zone electrophoresis method was developed for simultaneous determination of nine flavonoids, including two rare flavonols, in Tibetan medicine Anaphalis margaritacea. Baseline separation was performed at pH 9.6 with 25 mM Na2B4O7 and 10 mM NaH2PO4 buffer solution, 20 kV as driving voltage and 275 nm as detection wavelength. Repeatability tests showed that the R.S.D. of both intra- and inter-day migration times and peak areas were less than 5%. Recovery results ranged from 87.9% to 106.1%. Samples of A. margaritacea extracts were analyzed using the validated method, which is useful for its quality control. 相似文献
9.
The separation and determination of nitrophenol isomers by high-performance capillary zone electrophoresis 总被引:1,自引:0,他引:1
o-Nitrophenol, m-nitrophenol, and p-nitrophenol could well be separated by capillary zone electrophoresis (CZE) by only adjusting the run buffer with methanol. Efficiency up to 105 theoretical plates per meter was achieved. The effects of several important factors were investigated to find optimum conditions. The linear range, regression equation, and the recovery were given. This method possessed the advantages of simplicity, rapidity, and good reproducibility; it can be developed for the separation of practical samples in environment analysis. 相似文献
10.
A fast capillary zone electrophoresis (CZE) method, using dimethyl-β-cyclodextrin (DM-β-CD) as modifier, has been developed for the determination of three flavonoids (quercetin (QU), kaempferol (KA) and isorhamnetin (IS)) in the Chinese herbal extract from Hippophae rhamnoides and its medicinal preparation (Sindacon tablet). Optimum separation was achieved with 20 mM borate buffer at pH 10.0 containing 5 mg ml−1 of DM-β-CD. The applied voltage was 15 kV and the capillary temperature was kept constant at 25 °C. Regression equations revealed linear relationships (correlation coefficients: 0.9973, 0.9992 and 0.9996) between the peak area of each compound (QU, KA and IS) and its concentration. The relative standard deviations of migration times and peak areas were <1.53 and 4.14%, respectively. The effects of several CE parameters on the resolution were studied systematically. The contents of three flavonoids in H. rhamnoides were successfully determined with 4.5 min, with satisfactory repeatability and recovery. It was also tested that the possibilities of using this method for the determination of flavonoids in Chinese medicinal preparation. 相似文献
11.
In this paper, capillary zone electrophoresis with amperometric detection (CZE-AD) was firstly applied to the simultaneous separation and determination of nitroaniline positional isomers. The three analytes could be perfectly analyzed by using the buffer of extreme pH. The effects of several important factors were investigated to find optimum conditions. A carbon-disk electrode was used as working electrode. The optimal conditions were 40 mmol/L tartaric acid-sodium tartrate (pH 1.2) as running buffer, 17 kV as separation voltage and 1.10 V (versus saturated calomel reference electrode, SCE) as detection potential. Under the optimum conditions, o-, m- and p-nitroaniline were separated successfully and good linearity, reproducibility and recovery results were obtained. The detection limit for m-nitroaniline was as low as at 9.06 × 10−9 mol/L. This proposed method demonstrated long-term stability and reproducibility with relative standard deviations of less than 1.8% for migration time and 1.1% for peak areas. The utility of this method was demonstrated by monitoring dyestuff wastewater and the assay results were satisfactory. 相似文献
12.
Capability of fast analysis of a novel miniaturized capillary electrophoresis with carbon disk electrode amperometric detection (mini-CE-AD) system was demonstrated by determining acetaminophen and p-aminophenol in dosage forms. Factors influencing the separation and detection processes were examined and optimized. Under the optimum conditions, the end-capillary 300 μm carbon disc electrode amperometric detector offered favorable signal-to-noise characteristics at a relatively low potential (+600 mV versus Ag/AgCl) for detecting acetaminophen and p-aminophenol. Two analytes can been separated within 150 s in a 8.5 cm length capillary at a separation voltage of 2000 V using a Na2B4O7-KH2PO4 running buffer (pH 7.2). Acetaminophen and p-aminophenol could be detected down to the 1.4 × 10−6-5.9 × 10−7 mol L−1 level with linearity up to the 1.0 × 10−3 mol L−1 level examined. The inter-day repeatability for analytes in peak current (R.S.D. ≤ 2.3%) and migration times (R.S.D. ≤ 1.3%) were excellent. The proposed mini-CE-AD system should find a wide range of analytical applications in pharmaceutical formulations as an alternative to conventional CE and μ-CE. 相似文献
13.
Summary Capillary electrophoresis has been investigated as a novel experimental method for determination of the aggregation constants
of surfactants. The tendency of sodium cholate and sodium taurodeoxycholate to associate was studied in phosphate buffers
of pH 8.0 and pH 7.0, respectively. Stepwise aggregation equilibria of bile salt monomers has been described in terms of massbalance
equations. The Offord equation was used to model the electrophoretic mobility of the bile salt associates, and the experimental
mobility values could be fitted to the model. Interestingly, only even-membered aggregates-dimers and tetramers-besides the
monomers were proposed from the results of the curve-fitting for both bile salts. The aggregation constants calculated were
(in molar units): cholate logK
A2=1.37, logK
A4=4.98 taurodeoxycholate logK
A2=1.68, logK
A4=6.46. From these values, more pronounced aggregation of taurodeoxycholate starting at lower concentrations has been deduced,
supporting the back-to-back association model of bile salts. 相似文献
14.
Yunqiu Yu 《Analytica chimica acta》2004,523(1):15-20
A new capillary electrophoresis (CE) method for the determination of quinolizidine alkaloids in Sophora medicinal plants was developed. A total of seven alkaloid components (cytisine, sophocarpine, matrine, lehmannine, sophoranol, oxymatrine and oxysophocarpine) were separated within 15 min. The running buffer was a 50 mM phosphate buffer containing 1%HP-β-CD and 3.3% isopropanol. The linear calibration ranges were 5.50-88.0 μg ml−1 for cytisine and lehmannine, 5.00-88.0 μg ml−1 for sophocarpine and sophoranol, 5.60-89.6 μg ml−1 for matrine and oxysophocarpine, and 24.0-384 μg ml−1 for oxymatrine. The recoveries of the seven alkaloids were 96.0-102.9% with relative standard deviations from 1.50 to 3.00% (n = 5). The method was successfully applied to different Sophora medicinal plants including Sophora flavescens, Sophora tonkinensis and Sophora alopecuroides. 相似文献
15.
Michal Malý Milan Boublík Marijana Pocrnić Martin Ansorge Kateřina Lorinčíková Jana Svobodová Vlastimil Hruška Pavel Dubský Bohuslav Gaš 《Electrophoresis》2020,41(7-8):493-501
Thermodynamic acidity constants (acid or acid-base dissociation constants, sometimes called also as ionization constants) and limiting ionic mobilities (both of them at defined temperature, usually 25°C) are the fundamental physicochemical characteristics of a weak electrolyte, that is, weak acid or weak base or ampholyte. We introduce a novel method for determining the data of a weak electrolyte by the nonlinear regression of effective electrophoretic mobility versus buffer composition dependence when measured in a set of BGEs with various pH. To correct the experimental data for zero ionic strength we use the extended Debye-Hückel model and Onsager-Fuoss law with no simplifications. Contrary to contemporary approaches, the nonlinear regression is performed on limiting mobility data calculated by PeakMaster's correction engine, not on the raw experimental mobility data. Therefore, there is no requirement to perform all measurements at a constant ionic strength of the set of BGEs. We devised the computer program AnglerFish that performs the necessary calculations in a user-friendly fashion. All thermodynamic pKa values and limiting electrophoretic mobilities for arbitrarily charged substances having any number of ionic forms are calculated by one fit. The user input consists of the buffer composition of the set of BGEs and experimentally measured effective mobilities of the inspected weak electrolyte. 相似文献
16.
A nonaqueous capillary electrophoresis (NACE) method with direct on-column UV detection has been developed for the separation of the pharmaceutically important anthraquinones from the total grass of Xanthophytum attopvensis pierre extract. The separation of three main anthraquinones (1-hydroxy-2-methoxy-3-hydroxymethyl-9, 10-anthraquinone-1-O-β-d-glucoside (1), rubiadin- 1-methylether (2) and 1-methoxy-2-formyl-3-hydroxy-9, 10-anthraquinone (3)) was optimized with respect to concentration of sodium cholate (SC) and acetic acid, addition of acetonitrile (ACN), and applied voltage. Baseline separation was obtained for the three analytes within 5 min using a running buffer containing 50 mM sodium cholate (SC), 1.0% acetic acid and 40% ACN in methanol. The method of NACE for the separation and determination of bioactive ingredient in traditional Chinese medicines was discussed. 相似文献
17.
18.
Baoguo Sun Gregory Miller Wan Yee Lee Kelvin Ho Michael A. Crowe Leslie Partridge 《Journal of chromatography. A》2013,1271(1):163-169
Analytical methods were developed for a directed enzyme evolution research programme, which pursued high performance enzymes to produce high quality l-ribose using large scale biocatalytic reaction. A high throughput HPLC method with evaporative light-scattering detection was developed to test ribose and ribitol in the enzymatic reaction, a β-cyclobond 2000 analytical column separated ribose and ribitol in 2.3 min, a C18 guard column was used as an on-line filter to clean up the enzyme sample matrix and a short gradient was applied to wash the column, the enzymatic reaction solution can be directly injected after quenching. Total run time of each sample was approx. 4 min which provided capability of screening 4 × 96-well plates/day/instrument. Meanwhile, a capillary electrophoresis method was developed for the separation of ribose enantiomers, while 7-aminonaphthalene-1,3-disulfonic acid was used as derivatisation reagent and 25 mM tetraborate with 5 mM β-cyclodextrin was used as electrolyte. 0.35%of d-ribose in l-ribose can be detected which can be translated into 99.3% ee of l-ribose. Derivatisation reagent and sample matrix did not interfere with the measurement. 相似文献
19.
In this work how the microscopic properties of a molecular solvent affect the chemical environment of the protic ionic liquids (PILs) was analyzed. Using Reichardt’s dye as indicator of acidity, new acidity constant values for eight PILs (pKaPILs) were determined by spectrophotometric titration. Modifying the character hydrogen bonding donor of the molecular solvent it is possible to handle the PIL acid strength. Thus, we can turn basic PILs into acidic ones thereby the molecular solvent could be used as ‘additive’ for PILs, which allowed us to tune PILs design. 相似文献
20.
Veronika Šolínová Jiří Brynda Václav Šícha Josef Holub Bohumír Grűner Václav Kašička 《Electrophoresis》2021,42(7-8):910-919
Capillary electrophoresis (CE) has been applied for determination of the thermodynamic acidity constants (pKa) of the sulfamidoalkyl and sulfonamidoalkyl groups, the actual and limiting ionic mobilities and hydrodynamic radii of important compounds, eight carborane-based inhibitors of carbonic anhydrases, which are potential new anticancer drugs. Two types of carboranes were investigated, (i) icosahedral cobalt bis(dicarbollide)(1-) ion with sulfamidoalkyl moieties, and (ii) 7,8-nido-dicarbaundecaborate with sulfonamidoalkyl side chains. First, the mixed acidity constants, pKamix, of the sulfamidoalkyl and sulfonamidoalkyl groups of the above carboranes and their actual ionic mobilities were determined by nonlinear regression analysis of the pH dependences of their effective electrophoretic mobility measured by capillary electrophoresis in the pH range 8.00−12.25, at constant ionic strength (25 mM), and constant temperature (25°C). Second, the pKamix were recalculated to the thermodynamic pKas using the Debye–Hückel theory. The sulfamidoalkyl and sulfonamidoalkyl groups were found to be very weakly acidic with the pKas in the range 10.78−11.45 depending on the type of carborane cluster and on the position and length of the alkyl chain on the carborane scaffold. These pKas were in a good agreement with the pKas (10.67−11.27) obtained by new program AnglerFish (freeware at https://echmet.natur.cuni.cz ), which provides thermodynamic pKas and limiting ionic mobilities directly from the raw CE data. The absolute values of the limiting ionic mobilities of univalent and divalent carborane anions were in the range 18.3−27.8 TU (Tiselius unit, 1 × 10−9 m2/Vs), and 36.4−45.9 TU, respectively. The Stokes hydrodynamic radii of univalent and divalent carborane anions varied in the range 0.34−0.52 and 0.42−0.52 nm, respectively. 相似文献