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1.
The addition of calix[4]arenes to MeCN/H 2O or MeOH/MeCN/THF/H 2O mobile phases improves LC separation of benzene or uracil derivatives on Separon SGX C18 or Separon SGX NH 2 supports. Structure of the calixarenes and their host–guest supramolecular complexes with the analytes are discussed in context of the LC separation. 相似文献
2.
The effect of organic modifier concentration on retention and selectivity of two piperazine diastereomers in a typical n-octadecyl-bonded silica (ODS) column was investigated at pH 6.4 and pH 3.0 using phosphate-buffered acetonitrile (MeCN/H 2O) and methanol (MeOH/H 2O) mobile phases. The results show the logarithmic retention factors decrease with increasing organic concentration in a less rectilinear fashion in the MeCN/H 2O system than in the MeOH/H 2O system at high organic concentrations at both pHs. At pH 6.4, the MeOH/H 2O system provided significantly higher diastereomer selectivity than the MeCN/H 2O system, which can be ascribed to the hydrogen bonding interaction of methanol (as a hydrogen donor) with the piperazine amine moiety of the solute (as a hydrogen acceptor). At pH 3.0, both mobile phases provided high selectivity, in which both acetonitrile and methanol acted as hydrogen acceptors, while the protonated amine acted as the hydrogen donor. The effect of temperature on retention and selectivity was also studied in the two mobile phase systems at both pHs. It was found that at pH 6.4 the retention and selectivity were enthalpically driven in the MeOH/H 2O system, while entropically driven in the MeCN/H 2O system. However, the retention was entropically driven and the selectivity enthalpically driven in both systems at pH 3.0. Locally preferential solvating and hydrogen bonding effects are proposed to explain the anomalous retention and selectivity behaviors. 相似文献
3.
Summary The chromatographic behavior of twelve dansyl DL amino acids, one D isomer and eleven L isomers on RP 18W/UV 254, RP 18W/F 254s, and Sil C 18–50 UV 254 plates developed with aqueous—organic solutions containing bovine serum albumin (BSA) as chiral complexing agent has been extensively investigated. Enantiomeric resolution is highly dependent on mobile phase pH and ionic strength, and on the concentration of both BSA and organic modifier. All the racemates have been resolved within a development time of 1 h 30 min. The selectivity factors () for the dansyl amino acids have been compared with those from planar chromatography for the corresponding DNP, DNPy, and Fmoc amino acids, and with those of the same dansyl derivatives on a column prepared from BSA bound to silica gel. 相似文献
4.
A method is described for extraction, separation and quantification of 3 corticosteroids in tablets (triamcinolone, prednisolone and dexamethasone). The extraction was achieved using a solid phase extraction (SPE) on RP-18 cartridges. The steroids eluates were examined by HPLC. The chromatographic separation was carried out on Chromolith ® Performance RP-18e column, a new packing material consisting of monolithic rods of highly porous silica, using isocratic binary mobile phase of MeOH and H 2O in the ratio 1: 1. A diode array detector was used at 254 nm for detection. The method was validated for system suitability, linearity, precision, limits of detection, specificity, stability and robustness. The limits of detection were 6.25, 6.25 and 12.50 ng per 25 L injected volumes for them respectively. The recovery values of this method were between 89 and 101% and the reproducibility was within 6.86. 相似文献
5.
以Pt-TiO 2为光催化剂,研究了气相甲醛分别在35 h连续UV 254 nm光催化、O 3强化UV 254 nm(O 3+UV 254 nm)光催化和真空紫外(UV 254+185 nm)光催化中的降解效率,考察了副产物O 3的去除率,采用X射线光电子能谱(XPS)法分析Pt-TiO 2在不同光催化前后Pt的电子态和累积有机产物,研究纳米Pt对甲醛降解和O 3去除的强化机理. 连续光催化降解实验表明,以纳米Pt改性TiO 2可以同时增强甲醛和O 3的去除率,特别是O 3的去除率可提高3.1-3.4倍. 对催化剂C 1s和O 1s峰分别经分峰拟合处理后,发现Pt-TiO 2上累积的含羰基和羟基的有机物含量按以下顺序减少:UV 254 nm光催化 > O 3强化UV 254 nm光催化 > 真空紫外光催化,而在连续35 h光催化降解过程中,催化剂的失活现象却按相反的方向变得越来越不明显. 负载的金属Pt在O 3+UV 254 nm和UV 254+185nm光催化过程中被氧化成PtO ads和Pt 4+物种,而在UV 254 nm光催化过程中金属Pt未被氧化,所以推测是气相中的O 3和羟基自由基参与金属Pt的氧化过程. Pt-TiO 2表面高价态的Pt氧化物种可作为光生电子捕获中心,强化光生载流子的分离过程,增强Pt-TiO 2的光催化活性. Pt氧化物种可作为O 3分解的活化中心,使Pt-TiO 2对O 3的分解效率远高于纯TiO 2. 以XPS对比研究在三种不同光催化环境中Pt-TiO 2表面性质,可以解释在UV 254+185 nm光催化过程中纳米Pt对甲醛和O 3同时去除的强化机理,并说明了催化剂不失活的内在原因. 相似文献
6.
In this paper a phenyl-carbamate-propyl-β-cyclodextrin stationary phase was employed for the enantioseparation of several flavonoids, including flavanones and methoxyflavanones by using nano-liquid chromatography (nano-LC). The same stationary phase was also used for the diastereoisomeric separation of two flavanone glycosides. The compounds: flavanone, 2′-hydroxyflavanone, 4′-hydroxyflavanone, 6-hydroxyflavanone, 7-hydroxyflavanone, 4′-methoxyflavanone, 6-methoxyflavanone, 7-methoxyflavanone, hesperetin, hesperidin, naringenin and naringin were studied using reversed, polar organic and normal elution modes. The effect of the nature and composition of the mobile phase (organic modifier type, buffer and water content in the reversed phase mode) on the enantioresolution ( Rs), retention factor ( k) and enantioselectivity ( α) were investigated. Baseline resolution of all studied flavonoids, with the exception of 2′-hydroxyflavanone and naringin, was achieved in reversed phase mode using a mixture of MeOH/H 2O at different ratios as mobile phase. Good results, in terms of peak efficiency and short analysis time, were obtained adding 1% triethylammonium acetate pH 4.5 buffer to MeOH/H 2O mixture. The separation of the studied compounds was also performed in polar organic mode. By using 100% of MeOH as mobile phase, the resolution was achieved for the studied analytes, except for 7-hydroxyflavanone, 2′-hydroxyflavanone, naringenin, hesperidin and naringin. Normal mode was tested employing a mixture of EtOH/hexane/TFA as mobile phase achieving the enantiomeric and diastereomeric separation of only hesperetin and hesperidin, respectively. The use of nano-LC technique for the resolution of flavanones optical isomers allowed to achieve good resolutions in shorter analysis time compared to the results reported in literature with conventional HPLC. 相似文献
7.
High-performance thin-layer chromatography‒mass spectrometry (HPTLC‒MS) method was developed for the estimation of epimers (+)-catechin (CA) and (‒)-epicatechin (ECA) in Onosma bracteatum Wall. Resolving these epimers is challenging and so method optimization was done for the selection of the stationary phase and the mobile phase to achieve their coherent separation. To further increase the reliability of the obtained densitometric results, HPTLC–MS analysis was performed. The genus Onosma L. is a species-rich genus that exhibits complex patterns of morphological and karyological diversity, and highly debatable taxonomic approaches. Thus, many similar species are described based on morphological differences and often quite ambiguous. To facilitate the identification of O. bracteatum, separation was achieved using pre-coated silica gel 60 F254 HPTLC plate as the stationary phase and a mixture of diisopropyl ether–ethyl acetate–formic acid (9.0:0.2:0.7, V/V) as the mobile phase for the separation of epimers CA and ECA. Sample preparation, mobile phase selection and optimization were given importance to manage good resolution (RF) of these markers. Flavan-3-ols CA and ECA were identified and confirmed on the basis of RF and in situ UV and MS overlaid spectra with respective standards. The method was validated for linearity, inter-day precision, intra-day precision, repeatability, accuracy, specificity, limit of detection, and limit of quantification. The average recoveries for epimers CA and ECA from ethyl acetate extract fraction (MEF) were found 98.86 and 99.03% indicating the good reproducibility for each marker. The proposed validated HPTLC method is simple, accurate and reproducible and is the first report on the separation and quantification of the epimers CA and ECA in O. bracteatum using HPTLC–MS. 相似文献
8.
A simple and fast method was developed for simultaneous quantitative determination of three biologically active phenolic compounds i.e. quercetin, rutin and coumaric acid in flowers of Rhododendron arboreum using high-performance thin-layer chromatography (HPTLC). The separation was performed on TLC aluminium plates precoated with silica gel RP-18 F 254S. Good separation was achieved in the mobile phase of methanol-water-formic acid (40:57:3, v/ v/ v) and densitometric determination of these compounds was carried out at 280 nm in reflectance/absorbance mode. The linear regression data for the calibration plots showed a good linear relationship with r = 0.9971, 0.9953 and 0.9960 for quercetin, rutin and coumaric acid, respectively. Accuracy of the method was checked by recovery study conducted at two different levels with the average recovery of 99.90%, 99.02% and 99.16% for quercetin, rutin and coumaric acid, respectively. The present method is being reported first time and may be used for routine quality control of the flowers of R. arboreum. 相似文献
9.
Ruthenium catalysed oxidation of alkenes and monoenic fatty acids is reported. The study of the influence of cosolvents (H 2O/MeCN/X) shows that toxic CCl 4 initially used in the Sharpless system (H 2O/MeCN/CCl 4) can be avoided and demonstrates that the oxidative cleavage of CC bond could be accomplished in good yields with H 2O/MeCN/AcOEt solvent system in a ratio 3/2/2, respectively. 相似文献
10.
A mixture of cosolvents is described that significantly improves the solubility of most pharmaceutical compounds. The mixture consists of equal volumes of MeOH, 1,4‐dioxane, and MeCN, thereby containing polar and nonpolar solvents, and is referred to as MDM (from MeOH, dioxane, and MeCN). MDM is mixed with H 2O until the required composition is reached. The utility of this system is that it enables analytical measurements to be performed on a wide range of compounds where measurements would be impaired in aqueous solution. We present the physicochemical characteristics of MDM/H 2O mixtures (density, dielectric constant, p sKw) and the principles of p Ka measurement in this solvent/H 2O mixture. We also present p Ka values in H 2O of several drug compounds determined from values measured in MDM/H 2O mixtures. 相似文献
11.
A high-performance size-exclusion chromatography (SEC) system was coupled on-line to an electrospray ionization (ESI) interface
to detect gas-phase ions by an API 365 LC/MS/MS triple quadrupole analyzer. The SEC fractions of a strongly coloured freshwater
solution containing dissolved organic matter-humic substances (DOM-HS) were screened both by UV 254 and by ESI mass spectrometry (ESI-MS) in the full-scan mode within the m/z range of 100–2,900 amu in negative and positive polarities. The ESI-MS spectra were also collected by direct infusion of
the DOM-HS solution in both polarities. ESI-MS spectra did not primarily favour low mass compounds, and negative and positive
total ion chromatograms were parallel to the SEC elution profile obtained by UV 254 detection from DOM-HS solution. The UV 254 detection overestimated the SEC portion of higher size/mass solutes and underestimated that of solutes of smaller sizes/masses
as compared with the total ion chromatogram intensities in negative or positive polarities. The change of mass-weighted and
number-weighted average sizes/masses ( M
w and M
n) of different SEC fractions was fairly small, in contrast to UV 254 detection, with increasing elution volume. A reasonable explanation for the great differences between M
w and M
n values, obtained by UV 254 and ESI-MS detections for eight different SEC fractions, seems to be a supramolecular-type association of relatively small
components through weak dispersive forces. M
n values obtained by vapour-pressure osmometry for different SEC fractions were to some extent analogous with those of negative
and positive ESI-MS. The shapes obtained by either negative or positive polarities and calculated M
w and M
n values indicated a close structural similarity between each SEC fraction. Positive ion and negative ion spectra of different
humic fractions represented quite similar components, and there was no evidence for noteworthy occurrence of multiply charged
ions being able to lower mass distributions of negative ion spectra. The effect of nitrogen on the mass spectra seemed to
be unimportant, and the weak ions observed at even m/z values correspond most likely to the 13C counterparts of the more abundant 12C odd ions. No uncontrolled ESI fragmentation was observable and humic solutes seemed to be quite heat-resistant. Direct infusion
of the untreated DOM-HS solution and statistical calculation verified that the SEC-separated different fractions really represent
distinct entities of the original DOM-HS mixture. ESI-MS results support the opinion that the structural composition of humic
solutes in their original combined mixture resembles supramolecular-type associations of smaller molecular size entities possessing
similar structural functionalities. 相似文献
12.
Ethoxynonafluorobutane (ENFB) has been used as a component of new biphasic solvent mixtures. The suitability of several mixtures as solvent systems in countercurrent chromatography was tested. The applicability of the ENFB/2-PrOH/H 2O mixture to the separation of enantiomers, in combination with a fluorinated chiral selector (CS), was evaluated. N-Perfluoroundecanoyl-l-proline-3,5-dimethylanilide ( 2), analogous to the previously used N-dodecyl-l-proline-3,5-dimethylanilide ( 1), was synthesized for this purpose. The capacity of the new solvent system to retain the fluorinated CS in the fluorinated phase used as stationary was examined. Chiral selector 1 was applied in analogous conditions for comparative purposes. Additionally, MTBE/phosphate buffer solvent system was also used with the two CSs. The ENFB/2-PrOH/H 2O (25:35:40) mixture was found to be adequate in the enantioseparation of DNB-Leu and DNB-Leu- tBu. Enantioselectivity was maintained in the fluorinated solvent system without compromising eluting time. The complete separation of DNB-Leu- tBu was achieved and no leaks of CS to the mobile phase were detected. 相似文献
13.
A method is described for extraction and quantification of celecoxib in tablets. The extraction was achieved through centrifugation of the fine powder of the tablets in Acetonitrile (ACN). The extract was examined by LC. The chromatographic separation was carried out on a Caltrex AIII column, a relatively new packing material consisting of silica-bonded calix[8]arene, using isocratic binary mobile phase of ACN and H 2O (55%:45%, v/v). A diode array detector was used at 254 nm for detection. The method was validated for system suitability, linearity, precision, limits of detection and quantitation, specificity, stability and robustness. The limits of detection and quantitation were 0.122 and 0.488 μg mL ?1, respectively. The recovery value of this method was 101.88% and the reproducibility was within 2.08. 相似文献
14.
The photochemistry of several 2‐(2‐nitrophenyl)ethyl‐caged compounds including caged thymidine nucleosides was studied by nanosecond laser flash photolysis and stationary illumination experiments with quantitative HPLC analysis for quantum yields and product distribution. Effects of solvent basicity and acidity were investigated by varying the H 2O content and HCl concentration, respectively, in MeCN/H 2O mixtures. For all compounds 1 – 7 investigated, intramolecular H abstraction by the nitro group from the exocyclic α‐position with respect to the aryl moiety was found to be the primary process. The protolytic dissociation equilibrium of the resulting aci‐nitro compound was kinetically characterized in the 0.1 – 10 μs time region. In general, two reaction channels compete for the aci‐nitro compound and its anion: β‐elimination of the caged compound occurs from the anion, while from the undissociated aci‐nitro compound, a nitrosobenzene derivative is formed with no release of the caged compound. The yield ratio of these two reaction channels can be controlled through shifts in the protolytic dissociation equilibrium of the aci‐nitro compound. In solutions with either low basicity (H 2O‐free MeCN) or high acidity (higher concentration of HCl in H 2O/MeCN), two as yet unidentified products are formed, each one specifically for one of the mentioned conditions. 相似文献
15.
Chromatographing a model mixture of hydrocarbons with various carrier gases (helium, hydrogen, nitrogen, carbon dioxide, and nitrous oxide) was used to study the separation ability of monolithic silica capillary columns. It was revealed that the nature of the carrier gas strongly affects the retention time of the sorbates and the height equivalent to a theoretical plate (HETP) of the column, with the values of both these parameters decreasing in the series He > H 2 > N 2 > CO 2 ~ N 2O. This effect was found to be more pronounced for normal hydrocarbons than for their isomers. For chromatographing with CO 2 or N 2O under optimum conditions, the HETP was 25–30 μm, a value indicative of a higher specific efficiency of monolithic capillary columns. Theoretical correlations between the HETP and the properties of the mobile phase were considered. As a result, it was concluded that elevated pressures of the carrier gas, which are required to ensure the optimum operation of monolithic capillary columns, may affect the properties of the chromatographic system. 相似文献
16.
Host–guest complexation process of 5,17-bis-( N-tolyliminomethyl)-25,27-dipropoxycalix[4]arene with pyridine carboxylic acids by RP HPLC method (mobile phase – MeCN/H 2O, 86/14 by volume, LiChrosorb RP 18, UV detector, λ = 254 nm) had been studied. The binding constants and Gibbs free energies of the complexes 5,17-bis( N-tolyliminomethyl)-25,27-dipropoxycalix[4]arene with the pyridine carboxylic acids are within 584 to 1914 M ? 1 and ? 15.76 to ? 18.69 kJ/mol, respectively. It was shown by the molecular modelling that the complexes are stabilised by hydrogen bonds between carboxylic groups of the acids and nitrogen atoms of imino groups at the upper rim or oxygen atoms of the hydroxyl groups at the lower rim of the macrocycle. Linear dependence of the binding constants from the acid lipophilicity log P indicates the role of solvophobic interactions during the complexation process. 相似文献
17.
The experimentally known dependence in RP-HPLC of the retention factor k′ on octanol/water partition coefficient ( K ow) has been examined based on solvophobic theory. The result showed that the dependence provides a means for the evaluation of phase ratio ( Φ) of RP-HPLC columns, and of the equilibrium constant for a given compound and mobile phase. Using this theory, the phase ratio was evaluated for a set of seven different C18 columns (five having fully porous particles and two core–shell particles), and the equilibrium constants were calculated for four homologous series of compounds in two mobile phase systems. One mobile phase was methanol/aqueous solution of 0.1% H 3PO 4, and the other was acetonitrile/aqueous solution of 0.1% H 3PO 4. Besides providing the values for Φ for the evaluated columns, the results of the study indicated that for a specific composition of the mobile phase and for a given compound displaying only hydrophobic interactions, the equilibrium constant K( X) for different C-18 columns is basically the same. The data were further used to provide guidance in the selection of a chromatographic column for a specific separation based on K ow values and chemical structure of the analytes. The study indicated that the separation of compounds with identical polar groups (or no polar groups) and with very close values for the K ow cannot be achieved based only on hydrophobic interactions that dominate the separation on RP-type columns. Only column that displays polar interactions may provide a solution to such separations. For hydrocarbons with close K ow values, the separation cannot be achieved even on columns with some polarity. On the other hand, even compounds with equal K ow values, but with different functionalities can be separated on RP-HPLC columns without involving polar interactions. The compounds with different K ow values are expected to be easily separated on RP-HPLC columns. 相似文献
18.
The aim of the present study was to develop a fast, sensitive and reliable method for rapid screening of cephalosporin injectable dosage forms namely ceftazidime and ceftizoxime to the detection of counterfeit and substandard drugs that might be illegally commercialized. Ceftazidime, ceftizoxime and cefixime (IS) were separated in a X-Terra RP-18 column (250 × 4.60 mm ID × 5 ??) and DAD detector set at 290 and 260 nm. The mobile phase consisted of a mixture of methanol:water 20:80 ( v/v) at a flow rate of 1.0 mL min ?1. Additionally, in order to find the optimum pH value of separation the p K a values of studied compounds were determined by using two different methodologies. Aqueous p K a values of studied compounds have been determined by UV-spectrophotometry and liquid chromatography were used for the determination and direct characterization of the dissociation constants by using the dependence of the capacity factor on the pH of the mobile phase in 20% ( v/v) methanol?Cwater binary mixture in which separation was performed. The pH of the mobile phase was adjusted with 25 mM H 3PO 4 to 3.2. The method was shown to be linear, sensible, accurate, and reproducible over the range of analysis and it can be used to pharmaceutical formulations containing a single active ingredient within a short analysis time. 相似文献
19.
Abstract The separation and identification of triazine pesticides (ametryn, atrazine, cyanazine and simazine) was carried out on Nova Pak C 18 column (150 × 3.9mm). The mobile phase used was acetonitrile-water (65:35, v/v) adjusted to pH 4.5 with acetic acid. The flow rate of the mobile phase used was 1.0mL/min. The detection of the pesticides was carried out at 250 nm. The values of the separation factor (α) were in the range of 1.49–5.32 and the values of the resolution factors ( R s) were ranged from 1.18 to 2.99 for the separated pesticides. The developed HPLC method was used to determine the concentrations of the reported pesticides in the loamy soil samples. The recovery of the pesticides from soil samples was found to be about 50%. The relative standard deviation and limit of detection were in the range of 0.01–0.02 and 0.5–1.0 μg/mL respectively. 相似文献
20.
Simple, sensitive, selective, precise, and stability-indicating thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC) methods for the determination of mosapride and pantoprazole in pharmaceutical tablets were developed and validated as per the International Conference on Harmonization guidelines. The TLC method employs aluminum TLC plates precoated with silica gel 60F254 as the stationary phase and ethyl acetate/methanol/toluene (4:1:2, v/v/v) as the mobile phase to give compact spots for mosapride (R
f 0.73) and pantoprazole (R
f 0.45) separated from their degradation products; the chromatogram was scanned at 276 nm. The HPLC method utilizes a C18 column and a mobile phase consisting of acetonitrile/methanol/20 mM ammonium acetate (4:2:4, v/v/v) at a flow rate of 1.0 mL min−1 for the separation of mosapride (t
R 11.4) and pantoprazole (t
R 4.4) from their degradation products. Quantitation was achieved with UV detection at 280 nm. The same HPLC method was successfully used in performing calibrations in lower concentration ranges for both drugs in human plasma using ezetimibe as internal standard. The methods were validated in terms of accuracy, precision, linearity, limits of detection, and limits of quantification. Mosapride and pantoprazole were exposed to acid hydrolysis and then analyzed by the proposed methods. As the methods could effectively separate the drugs from their degradation products, these techniques can be employed as stability-indicating methods that have been successively applied to pharmaceutical formulations without interference from the excipients. Moreover the HPLC method was successfully used in the determination of both drugs in spiked human plasma. 相似文献
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