Jung Hag Park

Interpretation of normal-phase solvent strength scales based on linear solvation energy relationships using the solvatochromic parameters π, α and

Abstract An analysis of normal-phase solvent eluotropic strength (e0) and solute adsorption energy (S0) was carried out by use of linear salvation

Solvatochromic hydrogen bond donor acidity of aqueous binary solvent mixtures for reversed-phase liquid

Solvatochromic hydrogen bond (HB) donor acidity (αm) values for aqueous mixtures of methanol, ethanol, isopropanol, acetonitrile and tetrahydrofuran were measured by electronic absorption spectroscopy employing bis[α-(2-pyridyl)-benzylidine-3,4-dimethylaniline]bis(cyano)iron(II) as an indicator, and compared to available literature values. The HB donor acidity of all the aqueous organic mixtures increases in a nonlinear fashion as water is added to the organic solvent. For mixtures of acetonitrile and tetrahydrofuran, which are not acidic or are only slightly acidic, with water αm increases rapidly as a small amount of water is first added, then shows a plateau region, and finally slowly rises to the acidity value of water. In contrast, the αm for the mixtures of methanol, ethanol and isopropanol, which are quite acidic, increase slowly as the first small amount of water is added and then increase rapidly as the mixtures approaches pure water. Literature values of αm for water-methanol mixtures, which were determined from the DT(30) values of Reichardts betaine dye, showed a minimum in the plot of αmvs. volume fraction of organic component. It was also shown that the solvophobicity parameter (Sp) of methanol- and ethanol-water mixtures can be described by a combination of the dipolarity (πm*) and HB donor acidity (αm) of the mixtures.

Characterization of some normal-phase liquid chromatographic stationary phases based on linear solvation energy relationships

Abstract Characterization of a number of normal-phase liquid chromatography (NP-LC) stationary phases was attempted by estimating characteristic interaction constants for the stationary phases based on linear solvation energy relationships. Five characteristic interaction constants of the stationary phases, the lipophilicity (v), polarizability (r), dipolarity (s), hydrogen bond (HB) acceptor basicity (a) and HB donor acidity strength (b) were determined by multiple regression analyses of logarithmic capacity factors (k′) for a set of test solutes measured on them in the mobile phase of a given composition vs. the solute properties represented by characteristic molecular volume (Vx), excess polarization (R2), dipolarity/polarizability (π*), HB donor acidity (α) and HB acceptor basicity (β). Magnitudes of the five constants vary with the type of the stationary phases. The effect of polar modifier in the mobile phases on the interaction properties of the sorbents was also investigated.

Reversed-phase liquid chromatography of some positional isomers on calix[6]arene-p-sulfornate-bonded silica

SummaryA silica-bonded, calix[6]arene-p-sulfonate (CAPS) stationary phase has been used in the reversed-phase separation of mono-substituted phenol (cresol, methoxyphenol, nitrophenol, aminophenol and chlorophenol) regioisomers and some other aromatic positional isomers. Phenol isomers with polar and hydrogen-bonding groups (nitrophenol, aminophenol and methoxyphenol) are well resolved while isomers with nonpolar groups are not well resolved by highly aqueous, methanol mobile phases. Other aromatic positional isomers investigated are also well separated on CAPS in aqueous or highly aqueous, organic mobile phases with optimum retention.

Revisionist look at solvophobic driving forces in reversed-phase liquid chromatography. III. Comparison of the behavior of nonpolar and polar solutes

Abstract Recently we showed that in reversed-phase liquid chromatography (RRLC), solute methylene units are embedded in the bonded alkyl chains of the stationary phase. That is, the “partition mechanism”, not the “adsorption mechanism”, controls retention of methylene groups. We have also shown that the net interactions of the nonpolar groups of a solute with a nonpolar stationary phase contribute more to the overall free energy of transfer than does the solvophobic interaction in the mobile phase. The present work explores the behavior of several polar functional groups (Cl, OCH 3 , CHO, NO 2 , CN, and COOCH 3 ) in RPLC. In contrast to the behavior of methylene groups, the net interactions of more polar functional groups with the mobile phase are larger than are their net interactions with the stationary phase. Further, the data indicate that the free energy of transfer of a polar functional group in bonded phase RPLC is quite different from the free energy of transfer between the mobile phase and a bulk nonpolar liquid used to emulate the bonded phase. This implies that either sorbed mobile phase significantly influences the retention properties of polar groups in the bonded phase, or that the solute functional groups reside at the interface between the mobile and stationary phases.

Azithromycin as a new chiral selector in capillary electrophoresis

In capillary electrophoresis (CE), separation of enantiomers of a chiral compound can be achieved through the chiral interactions and/or complex formation between the chiral selector and the enantiomeric analytes on leaving their diastereomeric forms with different stability constants and hence different mobilities. A great number of chiral selectors have been employed in CE and among them macrocyclic antibiotics exhibited excellent enantioselective properties towards a wide number of racemic compounds. The use of azithromycin (AZM) as a chiral selector has not been reported previously. This work reports the use of AZM as a chiral selector for the enantiomeric separations of five chiral drugs and one amino acid (tryptophan) in CE. The enantioseparation is carried out using polar organic mixtures of acetonitrile (ACN), methanol (MeOH), acetic acid and triethylamine as run buffer. The influences of the chiral selector concentration, ACN/MeOH ratio, applied voltage and capillary temperature on enantioseparation are investigated. The results show that AZM is a viable chiral selector in CE for the enantioseparation of the type of chiral drugs investigated.

Fast separations of chiral β-blockers on a cellulose tris(3,5-dimethylphenylcarbamate)-coated zirconia monolithic column by capillary electrochromatography

Cellulose tris(3,5-dimethylphenylcarbamate) (CDMPC) is an excellent chiral selector for enantioseparation of a wide variety of chiral compounds. The monolithic chiral columns are becoming popular in liquid chromatography and capillary electrochromatography. In this work, we present the fast separation of chiral β-blockers on a CDMPC-modified zirconia monolithic column by capillary electrochromatography (CEC). The porous zirconia monolithic capillary column was prepared by using the sol-gel technology and then zirconia surface modified with CDMPC. The enantioseparations were performed in reversed-phase (RP) eluents of a phosphate solution (pH 4.4) modified with acetonitrile or alcohol. The enantioseparations of a set of eight chiral β-blockers were achieved in less than one minute. Influences of the applied voltage, column temperature, concentration of acetonitrile and the type of alcohol as the organic modifier in the mobile phase, and sample injection time on enantioseparation were investigated. CEC separations at the applied voltage of 10 kV and 15 °C in the ACN-modified mobile phase provided the best resolutions for the analytes studied. Run-to-run and day-to-day repeatabilities of the column in the RP-CEC separation were less than 1 and 2%, respectively.

Reversed phase liquid chromatographic separation of some mono-substituted phenols with calix[6]arene-ρ-sulfonate-modified eluents

SummaryThe utility of water-soluble calix[6]arene-ρ-sulfonate as a mobile phase additive has been investigated for the reversed phase liquid chromatographic separation of some monosubstituted phenol isomers. Retention factors and separation factors for regioisomers of methoxyphenol, aminophenol, and nitrophenol were measured using methanol — water and acetonitrile —water mobile phases of varying composition containing calix[6]arene-ρ-sulfonate, and the values were compared with those obtained using mobile phases containing no additive. It was observed that addition of calix[6]arene-ρ-sulfonate to both acetonitrile — water and methanol —water caused a reduction in the retention of the phenol isomers but generally increased the separation between them, thereby improving the overall separation efficiency.

Enantioseparation on cellulose dimethylphenylcarbamate-modified zirconia monolithic columns by reversed-phase capillary electrochromatography

This work reports the preparation of monolithic zirconia chiral columns for separation of enantiomeric compounds by capillary electrochromatography (CEC). Using sol-gel technology, a porous monolith having interconnected globular-like structure with through-pores is synthesized in the capillary column as a first step in the synthesis of monolithic zirconia chiral capillary columns. In the second step, the surface of the monolith is modified by coating with cellulose tris(3,5-dimethylphenylcarbamate) (CDMPC) as the chiral stationary phase to obtain a chiral column (CDMPCZM). The process of the preparation of the zirconia monolithic capillary column was investigated by varying the concentrations of the components of the sol solution including polyethylene glycol, water and acetic acid. CDMPCZM is mechanically stable and no bubble formation was detected with the applied current of up to 30 microA. The enantioseparation behavior of the CDMPCZM columns was investigated by separating a set of 10 representative chiral compounds by varying the applied voltage and pH and organic composition of the aqueous organic mobile phases.

Revisionist look at solvophobic driving forces in reversed-phase liquid chromatography IV. Partitioning vs. adsorption mechanism on various types of polymeric bonded phases

Abstract The partition and adsorption mechanisms of retention in reversed-phase liquid chromatography have been examined based on a comparison of the free energy of transfer of methylene groups from aqueous-organic mixtures to bulk hexadecane with those to a variety of polymeric bonded phases. The stationary phases studied include: conventional silica-based polymeric phases of various alkyl chain lengths, a so-called “horizontally polymerized” octadecyl phase on silica and a series of polybutadiene-coated zirconia phases. The data indicate that for methylene groups a partition-like mechanism is dominant on all phases. On the polybutadiene-coated zirconia and “horizontally polymerized” octadecyl phases the partition mechanism holds at all mobile phase compositions. In contrast on conventional polymeric silica phases the retention mechanism seems to become more adsorption-like at methanol compositions greater than about 70% (v/v).