RP-HPLC Retention Data of New 2-Amino-2-Oxazolines. An Approach of Their Lipophilic Properties

Abstract

A RP-HPLC procedure has been developed for measuring the capacity factor k' of a series of new 5-substituted-2-amino-2-oxazolines. the chromatographic behaviour measured on a μBondapack C₁₈ column with methanol-aqueous buffer as mobile phase was related to the volume fraction of methanol φ. the log k' value extrapolated to 0% organic modifier in the eluent (log k'_w) was chosen as a measure of the solute lipophilicity. A good correlation was found between the slope S and the intercept value (log k'_w) of the log k' versus φ straight lines for all these structurally related 2-amino-2-oxazolines.

Some parameters related either to chromatographic conditions or to chemical structure were shown to influence the capacity factor. A study made at different pH values indicated that log k'_w increased with the basicity of the mobile phase.

The influence of the eluent pH on the capacity factor of 2-amino-2-oxazolines was related to their pKa's values determined by a potentiometric method.

Since log k' is considered as a valuable indice of the lipophilicity, the determined values will be used for quantitative structure-activity relationship studies of these new class of structurally related compounds     

Solute Retention in Column Liquid Chromatography. VI. Enthalphy Entropy Compensation: The Column Temperature and Mobile-Phase Composition

Abstract

The concept of enthalpy-entropy compensation in “non-polar” reverse-phase (ODS) column liquid chromatography is examined in terms of the column temperature (10[ddot]-35[ddot]C) as well as mobile-phase composition (acidified water/tetrahydrofuran) for the solutes: phenol, p-nitrophenol, 2,4-dinitrophenol, o-chlorophenol, o-nitrophenol, 2,4-dimethylphenol, 2,4- dinitro-o-cresol, 4-chloro-m-cresol, and 2,4-dichlorophenol. Plots of log (solute capacity factor, k') against reciprocal column temperature, T^?1 exhibit approximate linearity only over the volume-fraction based mobile phase compositional range ?THF = 0 to 0.2. Substantial deviations occur beyond ?THF = 0.3. Plots of In k' against -ΔH[ddot] (compensation plots) yield a random distribution of data, indicating that what enthalpy-entropy compensation may exist for the systems studied is masked both in terms of temperature and mobile-phase composition. It is concluded that interaction(s) of the solutes with the stationary sorbent are more complex than has heretofore been supposed.     

The Study of Separation and Thermodynamics of Adsorption of the Enantiomers of Ethofumasate on a Modified Cellulose

Abstract

Cellulose and cellulose derivatives are biopolymers that are often used as stationary phases for the separation of enantiomers. Describing the mechanism of such separations is a difficult task due to the complexity of these phases. In the present study, direct enantiomeric resolution of ethofumesate has been achieved, using hexane as the mobile phase with various alcoholic modifiers on cellulose tri(3,5‐dimethylphenylcarbamate) chiral stationary phase (CDMPC CSP). The influence of the mobile phase composition and the column temperature on the chiral separation was studied. It was found that at a constant temperature and within a certain range of alcohol modifier concentration, the conformation of the polymeric phase, and the selective adsorption sites were not affected by alcohol modifier concentration. The type and the concentration of the alcoholic modifiers influenced the retention factor and the separation factor. Ethofumesate gained the best enantioseparation using sec‐butanol as alcoholic modifier at 25°C with α‐value 1.70. And the separation factor decreased with the increase of the column temperature. The van't Hoff plots were linear (R ²>0.96) for ethofumesate from 25°C to 50°C. That showed the enantioselective interactions do not change over the temperature range studied. Furthermore the values of ΔH° and ΔS° were both negative, which indicated an enthalpy‐driven separation. And the possible chiral recognition mechanism of the analyte and CDMPC was discussed. It was found that hydrogen bonding plays an important role on enantioseparation of CDMPC CSP. The inclusion and fitness of solute shape in the chiral cavity significantly contributed to the enantioseparation of solute.     

Influence of Bonded-Phase Column Type,Mobile Phase Composition,Temperature and Flow-Rate in the Analysis of Triglycerides by Reverse-Phase High Performance Liquid Chromatography

Abstract

Two chromatographic systems for RP-HPLC analysis of triglycerides, operating under isocratic conditions using octadecylsilane and octylisilane bonded phases, are described.

The influence of such chromatographic factors as bonded phase column type, mobile phase composition, temperature and flow rate on retention, analysis selectivity and efficiency, and separation of mixtures of homogeneous triglycerides was assessed. Linear relationships were established for the logarithm of the capacity factor and selectivity for each triglyceride in relation to temperature, the proportion of certain mobile phase components and flow rate.

The octadecylsilane bonded phase was more selective when analyzing triglycerides with a partition number below 48, while octylsilane was appropiate for separating mixtures of long chain saturated triglycerides to the detriment of the resolution of triglycerides with low partition numbers. ACN/ACE/THF (58/38/4) was a suitable mobile phase for use with the octadecylsilane bonded phase, and ACN/THF /H₂O (60/40/1) for the octylsilane bonded phase. A column temperature of 30°C and a flow rate of 1.5 mL/min resulted in acceptable resolution and analysis time in both systems.     

Liquid Chromatographic Characteristics of Ethylenethiourea with HPLC Carbon,Chiral, Polymer and Reverse-Phase Bonded Silica Columns

Abstract

Of the columns investigated, the graphitised carbon column provided the best chromatographic characteristics for the highly water-soluble compound ethylenethiourea (ETU). The stability of the carbon column in strongly acidic media permitted the incorporation of the phosphoric acid electrolyte into the 5% acetonitrile-in-water mobile phase. ETU eluted from the column in 200 s as a sharp symmetrical peak at a mobile phase flow rate of 1 mL/min and a column temperature of 35°C. The k' value was 1.72. ETU peak retention times and responses showed excellent repeatability with coefficients of variation of 0.28 and 1.40%, respectively, for 6 replicates with the high performance liquid chromatographic-electrochemical system using the graphitised carbon column. Although ETU eluted as a sharp symmetrical peak with the cyclodextrin chiral columns, their instability at low pH required post-column addition of the phosphoric acid electrolyte solution. ETU chromatographed poorly or degraded on the polymer columns. The chromatographic separation of ETU on the C-8 reverse-phase bonded silica column appeared to be due mainly to residual silanol groups. With the NH₂ bonded silica column ETU eluted immediately after the injection solvent.     

Effect of Temperature on HPLC Separations of Penicillins

Abstract

Reversed-phase high performance liquid chromatography (RP-HPLC) was used to separate in the same sample the following penicillins: amoxicillin, ampicillin, piperacillin, penicillin G, penicillin V and cloxacillin. After the chromatographic separation in isocratic elution conditions of the penicillins at ambient temperature, the effect of the column temperature on resolution was analyzed. The capacity factor of each penicillin was observed to increase with decreasing temperature, a linear relationship was obtained for a plot of ln k' versus 1/T. The results also showed changes in resolution between adjacent peaks being associated with differences in the selectivity factor (α).     

Development and validation of the stability-indicating LC-UV method for the determination of cefoselis sulphate

The stability-indicating LC assay method was developed and validated for quantitative determination of cefoselis sulphate in the presence of degradation products formed during the forced degradation studies. An isocratic, RP-HPLC method was developed with C-18 (250 × 4.6 mm, 5 μm) column and 12 mM ammonium acetate-acetonitrile (95:5 V/V) as a mobile phase. The flow rate of the mobile phase was 1.0 mL min⁻¹. Detection wavelength was 260 nm and temperature was 30°C. Cefoselis similarly to other cephalosporins was subjected to stress conditions of degradation in aqueous solutions including hydrolysis, oxidation, photolysis and thermal degradation. The developed method was validated with regard to linearity, accuracy, precision, selectivity and robustness. The method was applied successfully for identification and determination of cefoselis sulphate in pharmaceuticals and during kinetic studies.     

Studies on Steroids. CLXXVIII. Separation of Estrogen Glucuronides by High-Performance Liquid Chromatography

Abstract

Separation of monoglucuronides of estrone, estradiol, estriol and 16-epiestriol by high-performance liquid chromatography on a reversed-phase column has been carried out. The effects of pH and salt concentration of a mobile phase on the k' value were investigated with a TSK GEL LS-410 ODS-SIL column. Isomeric monoglucuronides of estriol and 16-epiestriol were distinctly separated on this column when 0.7% disodium hydrogen phosphate (pH 3.0)/tetrahydrofuran was used as a mobile phase.     

Comparison of Octadecyl-Bonded Alumina and Other Stationary Phases for Lipophilicity Estimation by High Performance Liquid Chromatography

Abstract

A recently developed octadecyl-bonded alumina stationary phase (ODA) was evaluated for determining the lipophilicities of organic compounds by high performance liquid chromatography. Using a column packed with this material and mobile phases consisting of methanol and aqueous buffers, the correlation between the octanol-water partition coefficients (log P's) of compounds of various chemical classes and the logarithms of their chromatographic capacity factors (log k's) was found to be superior to that obtained using columns packed with octadecylsilica, poly butadiene-coated alumina or octadecyl-derivanzed polystyrene-divinylbenzene copolymer. In contrast to results obtained with other columns, phenols and other hydrogen-bonding compounds did not need to be treated as a separate data set on the ODA column to obtain good correlations between log k's and log P's. The resistance of ODA to degradation by alkaline solvents allowed the use of a basic mobile phase (pH > 10) for suppressing ionization and determining the lipophilicities of organic bases which could not be evaluated within the stable pH range of ODS (pH 2–8). The log P's of five basic pharmaceutical compounds determined in this manner were found to be significantly higher than previously reported values. Evidence is presented which indicates that the previously reported log P values of these compounds are inaccurate, due to improper correction for ionization.     

Thin-layer chromatography with high-boiling mobile phase. part 2: Effect of temperature on retention characteristics in TLC with high-boiling mobile phases

A study has been undertaken on the effect of temperature on retention characteristics in thin-layer chromatography (TLC) with low-volatility mobile phases (MP). It is shown that temperature variations in TLC in melts bring about variations in both the relative retention values and, in some cases, in the order of migration of the chromatographic zones across the layer. The variation in the capacity factor k' with temperature agrees well with Martin's equation. To explain the temperature dependence of R_f one must, in general, take into account the variations with temperature in both the partition coefficient and the phase ratio. To describe the variation in R_f with temperature in TLC with low-volatile MP one can use an approximate equation in which In R_f is a linear function of 1/T. The experiments indicate that temperature is a major factor in TLC in melts.     

Stability-Specific HPLC Analysis of the Antiulcer Prostaglandin,Enprostil, in a Soft Elastic Gelatin Capsule Formulation

Abstract

This report describes a reverse-phase HPLC assay for the antiulcer drug, enprostil, formulated as a 0.3 mM solution (in propylene carbonate) filled into soft elastic gelatin capsules. The method uses: a 5 μm C18 column, a ternary (THF-methanol-phosphate buffer) mobile phase and 220 nm spectrophotometric detection to provide a sensitive and specific assay for enprostil and its major degradation products. The method satisfies the usual statistical criteria (recovery efficiency, response linearity, precision, lower quantitation limit) and performs well under various operating conditions as demonstrated by system suitability tests (analyte capacity factor dependence on column type, mobile phase composition, flow rate, and column temperature). We also demonstrate how a diode-array spectrophotometric detector     

The Separation of 12-Molybdophosphoric Acid from 12-Molybdosilicic Acid by Reverse Phase Liquid Chromatography

Abstract

The separation of 12-molybdophosphoric Acid (12-MPA) from 12-molybdosilicic (12-MSA) acid by reverse phase liquid chromatography is described with UV-visible detection. The system utilizes a commercially available styrene-divinylbenzene column (Hamilton PRP-1) and a acetonitrile-water mobile phase which is 0.1 F in HCLO₄ and 1.2 × 10^?2 in molybdate ion. In solutions with acetonitrile concentrations of between 30 and 35% (V/V), 12-MPA is completely retained on the column and 12-MSA has a capacity factor between 1.2 and .6. In solutions with acetonitrile concentrations of between 50 and 60% (V/V) 12-MSA is unretained and 12-MPA has a capacity factor between 2.2 and 1.6.

The detection limit is 5 × 10^?7 M phosphate or silicate anion in 100 uL of injected sample. The linear dynamic range extends to 1.3 × 10^?5 M for either anion. The relative standard deviation of the technique at the 5 × 10^?6 M level is 2% for both silicate and phosphate. The analysis of phosphate in silicate rock is described.     

Enantioselective separation of twelve pairs of enantiomers on polysaccharide‐based chiral stationary phases and thermodynamic analysis of separation mechanism

The enantioseparation of twelve pairs of structurally related 1‐aryl‐1‐indanone derivatives was studied in the normal‐phase mode using three different polysaccharide‐type chiral stationary phases, namely Chiralpak IB, Chiralpak IC, and Chiralpak ID. n‐Hexane/2‐propanol and n‐hexane/ethanol were employed as mobile phases. Among all the investigated chiral columns, Chiralpak IC exhibited the most universal and the best enantioseparation ability toward all the racemates, particularly with the mobile phase composed of n‐hexane/2‐propanol (90/10, v/v). Then the effects of column temperature on retention and enantioselectivity were examined in the range of 25–40°C. Satisfactory enantioseparation was obtained at ambient temperature. The natural logarithm of retention and separation factors (ln k and ln α) versus the reciprocal of absolute temperature (1/T) (Van't Hoff plots) were found to be linear for all racemates, indicating that the retention and separation mechanisms were independent of temperature in the range investigated. Then, the thermodynamic parameters (ΔΔH°, ΔΔS°, and ΔΔG°) were calculated from Van't Hoff plots. These values indicated that the solute transfer from the mobile to stationary phase was enthalpically favorable, and the process of enantioseparation was mainly enthalpy controlled. At last, the impact of small changes in molecular structures of the tested 1‐indanone derivatives on enantioseparation was also discussed.     

Reversed-Phase Ion-Pair High-Performance Liquid Chromatography of Phosphatidylinositols

Abstract

Reversed-phase ion-pal, high-performance liquid chromatographic (HPLC) separations of molecular species of phosphatidylinositols (PI) were studied. Mobile phases of acetonitrile-methanol-water containing various tetraalkylammonium phosphates (TAAP) were used for optimization. Stationary phases of macroporous polystyrene divinylbenzene (MPD), octylsilica, and octadecylsilica exhibited arying degrees of retentivity toward PI solutes. Without exception capacity factors (k') of PI on either alkylsilica or MPD increased with the alkyl chain length and the concentration of the quaternary ammonium counter ions evaluated. the results can be interpred in terms of an ion-pair retention mechanism. Logarithmic k' values were linearly related to the total number of carbons in TAAP. Perbenzoylation of PI yielded derivatives readily resolvable without the use of any mobile phase additive. Incorporation of TAAP to a mobile phase facilitated component separations of early-eluting perbenzoates. In HPLC with     

Liquid chromatographic separation and thermodynamic investigation of stereoisomers of darunavir on Chiralpak AD‐Hcolumn

Liquid chromatographic separation of stereoisomers of darunavir on Chiralpak AD‐H, a column containing the stationary phase coated with amylose tris(3,5‐dimethylphenylcarbamate) as a chiral selector, was studied under normal‐phase conditions at different temperatures between 20 and 50°C. The effect of quality and quantity of different polar organic modifiers viz: methanol, ethanol, 1‐propanol, and 2‐propanol in the mobile phase as well as column temperature on retention, separation, and resolution was investigated and optimized. The optimum separation was accomplished using a mobile phase composed of n‐hexane/ethanol/diethyl amine (80:20:0.1 v/v/v) at 40°C. Apparent thermodynamic parameters ΔH⁰ and ΔS* were derived from the Van't Hoff plots (lnk′ versus 1/T) and used to explain the strength of interactions between the stereoisomers and amylose tris(3,5‐dimethylphenylcarbamate) coated chiral stationary phase.     

Chiral ligand-exchange high-performance liquid chromatography with copper (II)-L-phenylalanine complexes for separation of 3,4-dimethoxy-α-methylphenylalanine racemes

L-3, 4-dimethoxy-α-methylphenylalanine (L-DMMD) is an important intermediate for the synthesis of 3-hydroxy-α-methyl-L-tyrosine (L-methyldopa). This paper describes an efficient, accurate, and low-priced method of high-performance liquid chromatography (HPLC) using chiral mobile phase and conventional C₁₈ column to separate L-DMMD from its enantiomers. The effects of ligands, copper salts, organic modifiers, pHs of mobile phase, and temperatures on the retention factors (k') and selectivity (α) were evaluated to achieve optimal separation performance. Then, thermal analysis of the optimal separation conditions was investigated as well. It was confirmed that the optimal mobile phase was composed of 20 % (v/v) methanol, 8 mM L-phenylalanine (L-Phe), and 4 mM cupric sulfate in water of pH 3.2, and the column temperature was set at 20 °C. Baseline separation of two enantiomers could be obtained through the conventional C₁₈ column with a resolution (R) of 3.18 in less than 18 min. Thermodynamic data (??H and ??S) obtained by Van't Hoff plots revealed the chiral separation was an enthalpy-controlled process. To the best of our knowledge, this is the first report regarding the enantioseparation of DMMD by chiral ligand-exchange HPLC.     

Temperature effects in Microcolumn Size Exclusion Chromatography

Abstract

Effects of column temperature on the column efficiency, retention time and stability of analytes were studied in microcolumn size-exclusion chromatography. Larger theoretical plates were achieved at column temperatures betwen 70 and 100 °C. In the constant-flow mode the retention time of analytes decreased with increasing column temperature, which was due mainly to thermal expansion of the mobile phase. When the column temperature was around or higher than the critical temperature of the mobile phase, the retention times of the analytes observed under supercritical pressure conditions still indicated dominancy of the size-exclusion mechanism, while another retention mechanism was involved under subcritical pressure conditions. In the case of the analysis of saccharides, the column temperature should be lower than 100 °C because oligosaccharides were decomposed at higher temperatures.     

反式氯氰菊酯对映异构体的分离

反式氯氰菊酯对映异构体的分离;拆分;手性固定相     

Ligand-exchange chromatography of amino acid enantiomers and its application to the biotransformation of DL-aspartic acid byPseudomonas dacunhae

Summary The separation of the D and L enantiomers of eighteen essential α amino acids has been investigated by ligand-exchange chromatography (LEC). The effect of column temperature on the retention times and resolution of individual amino acid enantiomers has been studied by varying the temperature from 25 to 50 °C for a mobile phase containing Cu²⁺ ions. By use of a temperature of 50 °C and Zn²⁺ in the mobile phase, eight of the eighteen amino acid enantiomers can be resolved sufficiently well for practical application. Only phenylalamine, tyrosine, and tryptophan can be separated by use of Ni²⁺ as complexation metal at 50 °C. LEC has been used to monitor the decarboxylation of racemic DL-aspartic acid byPseudomonas dacunhae. Analysis of DL amino acid enantiomers in different media was performed at column temperatures of 30 and 50°C by addition of 0.125 mM Cu²⁺ to the aqueous mobile phase. It was found that the analytical performance is most dependent on the identity of the metal used for complexation; the concentration of the metal was of secondary importance and the column temperature less important still.     

Studies on Steroids. CLXXXLV. Separation of Catechol Estrogen Monoglucuronides and Monosulfates by High-Performance Liquid Chromatography with Electrochemical Detection

Abstract

Separation of catechol estrogen monoglucuronides and mono-sulfates by high-performance liquid chromatography with electrochemical detection on a reversed-phase column has been carried out. The effects of composition and pH of mobile phases on the capacity factor were investigated with a TSKgel ODS-120T column. Each group of isomeric monoglucuronides and monosulfates of 2- and 4-hydroxyestrogens was efficiently resolved on this column when the 0.5% ammonium dihydrogen phosphate-tetrahydrofuran-acetonitrile system was used as a mobile phase.