H2O Mobile Phase Research Articles

Enantioseparation of cloprostenol on the polysaccharide chiral stationary phase: Influence of the mobile phase on enantioselective adsorption

Cloprostenol (CLO) is an important chiral drug widely used in veterinary practice. In high-performance liquid chromatography (HPLC), the acetonitrile/water system is more effective in the chiral resolution of CLO. The change in the ratio of acetonitrile and water has a great influence on the chiral selectivity of CLO. The enantioselective adsorption and nonselective adsorption of CLO on the polysaccharide stationary phase with three groups of mobile phases (Acetonitrile / 0.1 TFA; 95 Acetonitrile/5 H2O/0.1 TFA; 45 Acetonitrile/55 H2O/0.1 TFA) were determined and fitted with the subtraction fitting method (SFM). Adding a small amount of water to the mobile phase mainly reduced the enantioselective equilibrium adsorption constants Ks of (-)-CLO and thus changed the selectivity. Among them, the true separation factor (αtrue) of the 95 Acetonitrile/5 H2O mobile phase was as high as 92.86. Chiral preparation was performed on the basis of this mobile phase. The preparation performance in kkd (kilograms per kilogram of stationary phase purified compound per day) was 0.25 kg racemate/kg CSP/day.

Phosphorylated calix[4,8]arenes improve the RP HPLC separation of benzene derivatives

Aim. To study the effect of 5,11,17,23-tetrakis(diisopropoxyphosphonyl)-25,26,27,28-tetrapropoxycalix[4]arene and oсtаkis(diethoxyphosphoryloxy)-tert-butylcalix[8]аrene additives to the MeCN – H2O mobile phase (86:14) on the selectivity of the separation of aromatic compounds by the reversed-phase high performance liquid chromatography (RP HPLC) using a Separon SGX C18 support.Results and discussion. The process of complexation of phosphorylated calix[4,8]arenes with benzene derivatives in the mobile phase plays a key role in the RP HPLC separation of analytes. The stability constants of the inclusion complexes and the chromatographic separation coefficients of the analytes depend on the nature of the aromatic compounds and the cavity size of the calixarene macrocycle.Experimental part. The HPLC analysis was performed in acetonitrile – water (86:14) solution using a Separon SGX C18 column. The stability constants of the calixarene complexes were determined using the dependence of 1/k’ chromatographic parameters of benzene derivatives on the calixarene concentration in the mobile phase. Molecular modelling of the calixarene complexes was carried out using a Hyper Chem 8.0 program.Conclusions. The phosphorus-contained calixarenes due to their ability to form supramolecular complexes with aromatic molecules can be used as additives to the RP HPLC mobile phase and improve separation of benzene derivatives.Received: 14.05.2020Revised: 24.06.2020Accepted: 27.08.2020

Application of Chromatographic Columns with Nitrile and Phenyl Sorbents to the Analysis of Platinum Coordination Compounds

It was established that chromatographic columns with nitrile sorbents (Nova-Pak CN HP and Zorbax Eclipse XDB-CN) could be applied to the analysis of Pt(II) coordination compounds. The compounds could be analyzed by both reversed-phase chromatography (MeCN:H2O mobile phase, 3:97) and normal-phase chromatography (MeCN:H2O mobile phase, 96:4). The analytes were better resolved for normal-phase chromatography. Chromatography columns with various phenyl sorbents and a pentafluorophenyl sorbent (Discovery HS F5) could be used to analyze Pt(II) coordination compounds only by reversed-phase chromatography (MeCN:H2O mobile phase, 5:95). The properties of the nitrile and phenyl columns differed substantially for analysis of Pt(II) coordination compounds using mobile phases with >90% MeCN. Sorption of the Pt compounds to the nitrile columns at high MeCN contents was due to specific coordination interactions between the Pt atom and sorbent nitriles. In contrast to this, phenyl groups possessed practically no such ability.

Comparison of three different extraction methods and HPLC determination of the anthraquinones aloe‐emodine, emodine, rheine, chrysophanol and physcione in the bark of Rhamnus alpinus L. (Rhamnaceae)

Rhamnus alpinus L. (Rhamnaceae), a traditional plants in the flora of the Abruzzo region, is known to contain active anthraquinone secondary metabolites. However, the content of anthraquinones varies among R. alpinus samples depending on collection season and site. Thus, using simple, reliable and accurate analytical methods for the determination of anthraquinones in R. alpinus extracts allows comparative study of different methods of extraction. After a partial validation of an HPLC method for the simultaneous determination of five anthraquinones, aloe-emodine, rheine, emodine, chrysophanol and physcione, in the bark of R. alpinus, we compared three different methods of extraction. Anthraquinones were extracted from the bark of R. alpinus using different techniques (methanol maceration, ultrasonic and supercritical CO(2) extraction). Separation and quantification of anthraquinones were accomplished using a reversed-phase C(18) column with the mobile phase of H(2)O-methanol (40 : 60, v/v, 1% formic acid) at a wavelength of 254 nm. The qualitative analyses were also achieved at wavelength of 435 nm. All calibration curves were linear over the concentration range tested (10-200 mM) with the determination coefficients >or=0.991. The detection limits (S/N = 3) were 5 mM for each analytes. All five anthraquinones were found in the samples tested at concentrations reported in experimental data. The described HPLC method and optimised extraction procedure are simple, accurate and selective for separation and quantification of anthraquinones in the bark of R. alpinus and allow evaluation of the best extraction procedure between the tested assays.

Determination of the interconversion energy barrier of 2,3‐pentadienedioic acid enantiomers by HPLC. 2. On‐column interconversion

In this paper, an HPLC method is used to determine the enantiomerization barrier of 2,3-pentadienedioic acid enantiomers. The racemate of 2,3-pentadienedioic acid was separated by HPLC on a chiral CHIROBIOTIC T column with a 90:10 (100:0.5:0.5 MeOH/HOAc/TEA)/H2O mobile phase. Peak areas of enantiomers prior to (A(+)0, A(-)0) and after the separation (A(+), A(-)), were used for calculation of the rate constants and the enantiomerization barrier, as determined by computer-assisted peak deconvolution of the peak clusters on the chromatograms. The kinetic equation for irreversible reactions was used to determine the apparent enantiomerization rate constants and the interconversion energy barrier. The dependence of the apparent enantiomerization barrier (deltaG1(app), deltaG-1(app)) on temperature was used to determine the apparent activation enthalpy (deltaH1(app), deltaH(-1)app) and entropy (deltaS1(app), deltaS-1(app)) for the interconversion of 2,3-pentadienedioic acid enantiomers, where the coefficients 1 and -1 designate the interconversions (+) --> (-) and (-) --> (+), respectively.

Hydrodynamic Chromatography of Waxy Maize Starch

ABSTRACTA hydrodynamic column packed with solid beads chemically bonded with N‐methyl‐d‐glucamine residues was used with 90% dimethylsulfoxide (DMSO)‐H2O mobile phase as part of a chromatographic system to characterize jet‐cooked waxy maize starch. Software calculations based on signals from refractive index and dual‐angle light‐scattering detectors indicated the column could fractionate molecular weights up to ≈5 × 108. Calculated molecular weight values for the highest molecular weight sample was greatest at the lowest flow rate of 0.1 mL/min. Values of molecular weights and radii of gyration determined by the in‐line dual‐angle light‐scattering detector were significantly less than those determined with an off‐line multiangle light‐scattering detector that examined samples that had not traveled through the hydrodynamic column. This work has demonstrated the feasibility of using a hydrodynamic column to characterize waxy maize amylopectins. However, considerations of sample shear sensitivity and questions of in‐line light scattering detection show that further efforts are required to develop and optimize a chromatographic system to characterize very high molecular weight amylopectins.

Chromatographic selectivity for amino acid esters and alkali metal ions on a silica bonded calix[4]arene tetraester stationary phase

A silica bonded tetrameric calix[4]arene ester stationary phase has been used in the chromatographic separation of alkali metal ions and amino acid esters. Under reversed phase conditions, baseline resolution of a standard test mixture of benzamide, benzophenone and biphenyl was achieved using an MeOH—H2O mobile phase. In the chromatography of the amino acid ester hydrochlorides, retention appears to be related to the hydrophobicity of the esters studied, with tryptophan methyl ester being the longest retained.

Separation and Detection of Underivatized Amino Acids

Abstract Amino acids (AA) are separated on a Hamilton PRP-1 polystyrene divinylbenzene column with a basic CH3-CN:H2O mobile phase containing a tetraalkylammonium (R4N+) salt and a detector active counteranion. The underivatized AA are retained and separated as anions via a competing anion exchange process that occurs between the AA anion and the counteranion towards the R4N+ salt, an equilibrium amount of which is maintained on the stationary phase according to the mobile phase conditions. An indirect detection (ID) is possible because of displacement of the detector active counteranion. Indirect photometric (IPD), fluorometric (IFD), or electrochemical (IED) detection is possible by using a counteranion that absorbs, fluoresces, or is electrochemically active. Parameters that influence retention and resolution are AA side chain structure and mobile phase pH. R4N+ structure and concentration, organic modifier, and counteranion selectivity and concentration. These same parameters, in addition to the count...

HPLC Determination of Sugars in Raw and Baked Sweet Potatoes

ABSTRACTIsocratic HPLC techniques were developed for the quantitative analysis of sugars in raw and baked sweet potato roots. The major sugars in raw roots: sucrose, glucose, and fructose, were quantitated with a cation exchange resin column (Aminex HPX‐87C) heated to 75°C using HPLC‐grade H2O as the mobile phase and refractive index detection. The major sugars in baked roots (convection oven or microwaved) were maltose, sucrose, glucose, and fructose. They were quantitated with an aminopropyl bonded phase column (Bio‐Sil Amino 5S) at 21°C using a 70% CH3CN:30% H2O mobile phase and refractive index detection. Over 95% recoveries of all sugars added to sweet potato roots were obtained.