Q. S. Wang

Separation of peptides by pressurized capillary electrochromatography

A pressurized electrochromatography (pCEC) instrument with gradient capability was used in this work for separation of peptides. Three separation modes, namely, pCEC, high-performance liquid chromatography and capillary electrophoresiscan be carried out with the instrument. In pCEC mode, the mobile phase is driven by both electroosmotic flow and pressurized flow, facilitating fine-tuning in selectivity of neutral and charged species. A continuous gradient elution can be carried out conveniently on this instrument, which demonstrates that it is more powerful than isocratic pCEC for separation of complicated samples. The effects of applied voltage, supplementary pressure and ion-pairing agents on separation of peptides in gradient pCEC were investigated. The effects of flow-rate of the pump and the volume of the mixer on resolution were also evaluated.

REVIEW OF RESEARCH ON QUANTITATIVE STRUCTURE-RETENTION RELATIONSHIPS IN THIN-LAYER CHROMATOGRAPHY

A review is given on the quantitative structure-retention relationship (QSRR) in TLC. The establishment of QSRR equations is described, which is based on physico-chemical parameters, non-specific parameters, topological indices, and a combination of physico-chemical parameters. The application of QSRR for prediction of retention, determination of lipophilicity, evaluation of some physico-chemical parameters of chemicals, evaluation of biological activity of compounds, and explanation of separation mechanisms are also reviewed.

Fast and precise determination of phenthoate and its enantiomeric ratio in soil by the matrix solid-phase dispersion method and liquid chromatography.

A fast and precise method was developed for the determination of phenthoate and its enantiomeric ratio (ER) in three soil samples. A recently developed sample pretreatment technology--matrix solid-phase dispersion (MSPD) was used to extract phenthoate simply and effectively. MSPD conditions, i.e. solid-phase Florisil amount, water content of Florisil-soil mixture, the constituent and volume of the eluting solvent, were optimized stepwise. The MSPD extract was directly used for quantitative determination of phenthoate by silica-based high-performance liquid chromatography (HPLC) with UV detection. The recoveries of phenthoate from three different types of soils fortified at three levels of 0.1, 1, 10 microg/g ranged from 75 to 94% with RSDs of 1.5-6.5%. On this basis, phenthoate was further isolated from the remainder of MSPD extract by silica-based HPLC and then ER determined on HPLC with cellulose tris-3, 5-dimethylphenylcarbamate as chiral stationary phase. The ERs determined in the soils spiked with racemic or enantiomer-enriched phenthoate agreed sufficiently well with those in the corresponding standard solutions. Finally, the proposed method was successfully applied to the study of enantioselective degradation of phenthoate in the three soils under laboratory conditions. High enantioselectivity was observed in the two alkaline soils with (+)-enantiomer degrading faster than the (-)-enantiomer, while there was little to no enantioselectivity in the acidic soil. The methodology can be used to study the enantioselective environmental behavior of chiral pollutants.

Enantioseparation of fourteen O-ethyl O-phenyl N-isopropyl phosphoroamidothioates by high-performance liquid chromatography on a chiral stationary phase

Abstract A series of fourteen O-ethyl O-phenyl N-isopropyl phosphoroamidothioate enantiomers containing a phosphorus atom as a chiral center have been separated by high-performance liquid chromatography on a Pirkle model chiral stationary phase. Chromatography data, the capacity factor (k′) and the separation factor (α) of all solutes are presented. The influence of chromatographic conditions was investigated. The probable mechanism for chiral recognition is proposed.

Direct Chiral High Performance Liquid Chromatography Separation of O,O-Diethyl-(p-methyl-benzene-sulfonamido)- Aryl (Alkyl)-Methylphosphonate

Abstract The enantiomers of a series of twelve O,O-diethyl, (p-methyl-benzenesulfonamido), aryl(alkyl)-methylphosphonates have been separated by high performance liquid chromatography on a Pirkle model chiral stationary phase. Chromatographic data and a chiral recognition model are presented for the separation of these organic phosphorus enantiomers on the chiral phase. The influence of column temperature and flow rate of mobile phase has been described.

Influence of the Structure of Organic Phosphonate Compounds on Chiral Separation on a Pirkle Type Chiral Stationary Phase

SummaryThe enantiomers of eightO,O-dialkyl-2-benzyloxycarbonyl-aminoarylmethyl-phosphonates are directly separated on anN-(3,5-dinitrobenzoyl)leucine (DNBleu) column. The influence of the mobile phase composition and the column temperature on the retention and the enantioselectivity are investigated. The influence of the length and steric hindrance of alkoxyl groups of the phosphonate ester and the nature of the substituentp-Cl and pH on the benzene ring which is attached to the chiral carbon atom on chiral separation are discussed also.

Evaluation of the retention characteristics of ferrocene-bonded silica stationary phase and other silica-based reversed phases for HPLC using linear solvation energy relationships

SummaryThe similarities and differences in retention characteristics of ferrocene-bonded and other three silica-based phases have been elucidated by the use of linear solvation energy relation-ships (LESRs). These phases were investigated in a common mobile phase. The results of LSERs on ferrocene-bonded phases are quite different from other silica-based phases. Retention on all other silica-based phases is dominated by two factors: the solute size and hydrogen bond acceptor basicity. While on ferrocene-bonded silica phase, the retention is dominated by excess molar refraction and hydrogen bond acceptor basicity. The s coefficient is small but positive which is unlike the common reversed phase stationary phases. Ther coefficient is much larger and positive showed the new phase has stronger π-π interaction to solutes than all other phases, and high selectivity to polyaromotic hydrocarbons.

Relationship between the lipophilicity and specific hydrophobic surface area of some pesticides by RP-HPLC and HPTLC

SummaryUsing methanol-water mixtures as the mobile phases, the retention behaviors of thirty-seven pesticides were determined in RP-HPLC and RP-HPTLC. Regular retention behavior was observed for all the investigated pesticides: theirRm and logk values decreasing linearly with increasing concentration of methanol in the mobile phase. The lipophilicity and specific hydrophobic surface area values for each compound were obtained and they have a good linear relationship. Although the chemical structures of these pesticides were different, factor analysis proved that the lipophilicity and specific hydrophobic surface area of these compounds have much in common, and the insecticides, fungicides and herbicides could not be distinguished from each other according to their lipophilicity parameters obtained from chromatography method.

PREDICTION OF RETENTION OF O-ETHYL, O-ARYL AND N-ISOPROPYL PHOSPHOROAMIDOTHIOATES IN RP-HPLC FROM MOLECULAR STRUCTURE PARAMETERS

SummaryMulti-variable regression analysis between lnkw, c (in retention equation lnk′=lnkw+cCb) and molecular structure parameters, including hydrophobicity, electric effect, field effect and position-specific effect constant, was carried out with O-ethyl, O-aryl and N-isopropyl phosphoroamidothioates as test solutes. With these quantitative relationships, the retention behaviour of these solutes for different mobile phase compositions was predicted. The results showed that there are only 26.7% of total, experimentally measured, capacity factors with relative deviations larger than 5% and only 2.2% with deviations larger than 10%, which means that it is possible to apply the method reported to predict retention values for qualitative purposes for different mobile phase compositions.

Enantiomer separation and preparation of five organophosphorus compounds and their biological activities.

SummaryThe direct enantiomeric resolution of five O-aryl O-alkyl N-alkyl-phosphoramidothioates was carried out and their pure enantiomers were prepared on a commercially available Pirkle model chiral column (OA-4700). Absolute configurations of the enantiomers were determined by circular dichroism (CD) spectroscopy. S-enantiomers were the first compounds to elute chromatographically and the chromatographic elution order was in accordance with the results of computer simulating calculation. The biological activity test suggested that all the S-enantiomers were more active than R-enantiomers in killing barnyard grass.