Alcohol Modifier In Mobile Phase Research Articles

COMPARATIVE STUDIES OF ENANTIOSEPARATION OF SOME AMINO ACIDS AND N-PROTECTED AMINO ACIDS IN NORMAL PHASE HPLC AND ANALYSIS OF UNUSUAL PEAK SHAPE

Comparative studies of enantioseparation of some amino acids and N-protected amino acids were performed using a Chiralpak IA column in normal phases HPLC. Better resolution results were obtained for N-protected amino acids compared with the studied amino acids at the same conditions. The effects of type and concentration of alcohol modifier in mobile phase, concentration of acidic additive trifluoroacetic acid, and column temperature on enantioseparation were also investigated. The experimental results showed that the separation factor and resolution factor were both high when ethanol was used as alcohol modifier in mobile phase. When the mobile phase contained 35% (v/v) ethanol, the separation factor of all the enantiomers was the highest. A trace amount of trifluoroacetic acid promotes enantioseparation regardless of the nature of the chiral solutes. The retention time of investigated enantiomers decreased with the increase of column temperature. The chromatographic peak shape of enantiomers separation was almost symmetrical except for the resolution of phenylalanine and 3-(3,4-dihydroxyphenyl)alanine, in which chromatographic peak of the first eluted enantiomer was unusual lower and wider than that of the second eluted enantiomer. The mechanism of the unusual peak shape from enantioseparation of phenylalanine and 3-(3,4-dihydroxyphenyl)alanine was analyzed.

Reversal of elution order of N‐(2,4‐dinitrophenyl)‐proline and N‐(2,4‐dinitrophenyl)‐serine in HPLC by BSA chiral stationary phase

N-(2,4-dinitrophenyl)-proline and N-(2,4-dinitrophenyl)-serine were enantiomerically resolved on the BSA chiral stationary phase by HPLC in reversed-phase mode. Effects of chromatographic conditions on enantioseparation and elution order have been investigated in detail. For these two samples, reversal of enantiomer elution order was observed by changing buffer pH, the content of acetonitrile, or alcohol modifiers in mobile phase, which is firstly reported in the BSA chiral stationary phase studies. More interestingly, combined effect between buffer pH and the content of acetonitrile was also observed. In addition, coelution range of enantiomers varied along with the content of acetonitrile in mobile phase.

Unusual chromatographic enantioseparation behavior of naproxen on an immobilized polysaccharide-based chiral stationary phase

Enantioseparation of naproxen was performed on an immobilized polysaccharide-based chiral stationary phase (CSP), Chiralpak IA, in the normal-phase mode. The effects of polar alcohol modifier in mobile phase and column temperature on retention, enantioseparation, and elution order were investigated. Two unusual phenomena were observed. One was solvent-induced reversal of elution order for the two enantiomers. Not only the type but also the content of polar alcohol modifier could induce the reversal. Another uncommon phenomenon was peak deformation under some chromatographic conditions.

Influence of the Alcoholic Modifier on the Enantioseparation of Organophosphonate Derivatives on Cellulose tris(3,5-Dimethylphenylcarbamate) Chiral Stationary Phase Under Normal Phase Mode

The enantiomers of fifteen O,O-dialkyl-2-benzyloxycarbonyl- aminoarylmethyl-phosphonates are directly separated on cellulose tris(3,5-dimethyl-phenylcarbamate) chiral stationary phase using different alcohols as organic mobile phase modifier. The influence of the position and properties of substituents in benzene ring, the length and steric hindrance of alkoxyl groups of the phosphonate ester on the chiral separation were discussed using different alcohol modifiers namely, ethanol, n-propyl alcohol, isopropyl alcohol, and n-butyl alcohol. The study indicates that with the use of different alcohol modifiers in mobile phase, the capacity factor (k) was in the order of k EtOH<k PrOH<k BuOH<k i-PrOH. The results also show that using n-butyl alcohol or isopropyl alcohol as mobile phase modifier achieve better chiral separation for these organophosphonate derivatives than that using ethanol or n-propyl alcohol.

Direct optical resolution of the enantiomers of axially chiral compounds by high-performance liquid chromatography on cellulose tris-(3,5-dimethylphenylcarbamate) stationary phase

A chiral stationary phase(CSP) was prepared by coating amylose tris-(3,5-dimethylphenylcarbamate) onto aminopropylated spherical silica gel. The enantioselective chromatographic separation of a series of biphenyl compounds with antihepatitis activity was performed for the first time on CSP. The effect of alcohol modifiers in mobile phase was investigated. The mobile phases used in the study were hexane modified by ethanol, 1-propanol, 1-butanol or 2-propanol. It was found that the retention times and the separation of the enantiomers of biphenyl compounds on the CSP were dramatically influenced by the nature of alcohols in the mobile phase, and the best alcohol modifier for some compounds was ethanol. The interaction between the stationary phase and samples was also discussed.

Effects of Alcohol Modifiers on the Separation of 1-Alkoxycarbonyl-Alkyl-Pyrrolidine-3-Carboxylic Acid Alkyl Ester Enantiomers on Polysaccharide-Based Stationary Phases

1-Alkoxycarbonylalkyl-pyrrolidine-3-carboxylic acid alkyl esters (1, 2, 3 and 4, see Figure 1 for structures) are the synthetic intermediates used for the large-scale synthesis of PD 151832. PD 151832 is a highly potent m1 subtype selective muscarinic agonist expected to be useful for patients with Alzheimer's disease. The mobile phase consisting of hexane/2-propanol/diethylamine has been previously shown to resolve the enantiomers of compounds 1, 2 and 4 on a Chiralpak AS column and compound 3 on a Chiralpak AD column.1 In the current study, the nature of the alcohol modifier in mobile phase was varied and the resulting change in stereoselectivity was found to depend on compound and column type. Superior separations can often be achieved by using an alcohol modifier other than the commonly used 2-propanol or ethanol on the same column. The use of different alcohol modifiers in mobile phase to enhance the enantiomeric resolution can provide useful and less expensive alternatives to the approach of using multiple columns in chiral methodology development.