Fujio Morishita

Separation of drugs by packed-column supercritical fluid chromatography.

Packed-column supercritical fluid chromatography (pSFC) has been expected to analyze various kinds of compounds. Many researchers have expected a new chromatographic technique that overcomes the limitations of other techniques, HPLC and GC. In pharmaceutical development, chromatography plays an important role in the evaluation of safety and efficacy of a new compound. This article provides an overview of the separation of drugs by pSFC. The effects of the chromatographic parameters were studied for the separation of steroids. In chiral separation, the successful results were shown and compared with HPLC.

Thermodynamic study and separation mechanism of diltiazem optical isomers in packed-column supercritical fluid chromatography

Abstract Cellulose tris(4-chlorophenylcarbamate) coated on silica was used as a chiral stationary phase for the separation of diltiazem (a Ca-channel blocker) optical isomers in packed-column supercritical fluid chromatography. The effect of temperature on the separation of the cis- and trans-enantiomers was studied in detail. The Van’t Hoff plots for the retention were found to be curves, while those for the selectivity were found to be linear. The chiral separation of cis-enantiomers was improved with a decrease in temperature, whereas that of trans-enantiomers was improved with an increase in temperature. To obtain a better understanding of the difference in the separations of cis- and trans-enantiomers, the temperature dependence of enantioselectivities was studied to determine the thermodynamic parameters ΔΔH°, ΔΔS°, and Tiso. The thermodynamic parameters revealed that the separation of trans-enantiomers was entropy-controlled in the range of temperature examined, whereas enthalpy-controlled separation was observed for cis-enantiomers. The separations of both cis- and trans-enantiomers, however, were enthalpy-controlled in normal-phase HPLC. The separations of the related compounds, 3-hydroxy isomers, were compared with those of diltiazem isomers. In addition, the differences in separation mechanisms between cis- and trans-enantiomers of diltiazem optical isomers are discussed by means of three-dimensional structures.

Chiral resolution of four optical isomers of diltiazem hydrochloride on Chiralcel columns by packed-column supercritical fluid chromatography

The optical isomers of diltiazem hydrochloride Ca-channel blocker were separated by packed-column sub- and/or supercritical fluid chromatography (p-SubFC and/or p-SFC) on a column of modified cellulose coated onto silica, using a mixture of carbon dioxide with a polar modifier and additive. The effect of parameters (Chiralcel columns, modifiers, additive, pressure and temperature) was investigated systematically, and the interactions between the diltiazem optical isomers and chiral stationary phase were discussed. Four optical isomers of diltiazem hydrochloride were achieved with baseline resolution on the Chiralcel OD column within 8 min. To determine three optical impurities in diltiazem hydrochloride, the precision, accuracy, linearity and detection limit were investigated, and the results were sufficiently acceptable. In addition, the resolutions in p-SFC were compared with those in high-performance liquid chromatography.

Measurement of Retention Indexes on n-Alkane Scale in Reversed-Phase Liquid Chromatography and their Prediction from Molecular Structures

Abstract A method was proposed in which the retention indexes (RI) defined on the n-alkane scale were measured by using 1-phenylalkane homologous series as reference compounds. Good agreement was observed between the RI values obtained with this method and those determined using n-alkanes as the reference. An attempt was made to predict the RIs based on the additivity for the constitutive atomic groups. The RIs were estimated with considerable accuracy by using increments of substituents themselves and positional increments between substituents. It was possible to distinguish methylnitroaniline isomers by comparison of the calculated RI values with the observed values.

Retention behavior of synthetic corticosteroids in packed-column supercritical fluid chromatography

The retention behavior of the synthetic corticosteroids used in a therapy was investigated using packed-column supercritical fluid chromatography (SFC) modified from a commercial liquid chromatographic system. The influence of the stationary phase, modifiers, column pressure and temperature was studied systematically. An aminopropyl-bound silica column and carbon dioxide modified with methanol were selected. The selectivity and separation efficiency in the packed-column SFC were superior to those in the existing normal- and reversed-phase liquid chromatographic conditions. Seven polar corticosteroids, possessing 1 to 4 hydroxyl groups, showed baseline separation within 6.5 min on a modifier gradient.

Prediction of molecular structures of thiols and sulphides by retention indices

Abstract A method is discussed, in which the presence of thiols and sulphides is confirmed by combination of a post-column reaction and flame photometric detection. The molecular structures are determined by comparing the calculated and the observed retention indices. The retention indices of these compounds can be given in terms of the increment due to a mercapto group or a thio group and the correction values for the shielding effect of these groups by neighbouring carbon atoms.

Identification of some polycyclic nitrogen-containing compounds in coal-derived oil

A systematic method for the identification of aza-arenes in coal-derived oil was developed. The basic nitrogen-containing substances were extracted with 6 M hydrochloric acid and fractionated sequentially by using gel chromatography and thin-layer chromatography (TLC) on an alumina plate. The aza-arenes in these fractions were separated by using glass capillary gas chromatography. Individual compounds in the column effluent were trapped in a system consisting of a valve for flow switching and a trapping tube made from a glass capillary. The fluorescence spectra of nanogram to subnanogram amounts of trapped compounds were measured. Some attempts were made to identify components based on their TLC RF values and their fluorescence spectra, in addition to their mass spectra.

Laser-Pyrolysis-Gas Chromatography of Semicarbazones of Carbonyl Compounds

Abstract Semicarbazones of carbonyl compounds were degraded by laser heating. The characteristic alkenes, which keep the structure and the carbon number of the original carbonyl compound and whose double bond indicates the position of the carbonyl group, are obtained in high yield. Lighter hydrocarbons also reflect the original structure.

Prediction of molecular structures of aza-arenes in synthetic oil derived from horonai coal.

The basic nitrogen-containing substances in synthetic oil derived from Horonai coal were extracted with 6M hydrochloric acid and fractionated sequentially by gel permeation chromatography using TSK G1000 HXL gel and by thin layer chromatography (TLC) on an alumina plate. After separation of each TLC fraction by using GC-MS, some peaks were assigned to tricyclic aza-arenes on the basis of their mass spectra and retention values. Each aza-arene eluted from a GC capillary column was collected and its fluorescence spectrum was measured. Molecular structures of aza-arenes were predicted on the basis of the combination of information from the mass and fluorescence spectra and the TLC fractionation. Mass spectra afford information on the number of carbon atoms in alkyl chains. Fluorescence spectra are capable of distinguishing between the ring structures of phenanthrene and an-thracene types. The Rf value in TLC is determined mainly by the interaction between the nitrogen atom of the solute and aluminum ion on the plate surface; the TLC fraction number af-fords information on interference from atomic groups on the ring, that is, information on the positional relationship between the nitrogen atom and substituents or the ring. By the combination of above information, exsistence of some aza-arenes was inferred, which were not available easily; e. g. benz [f] isoquinoline, benz [h] isoquinoline, 3-methylbenzo [f] quinoline and/or 6-methylbenzo [c] quinoline.

Laser-pyrolysis-gas chromatography of derivatives of carbonyl compounds

カルボニル化合物の誘導体を試料に選び,レーザー光で分解したときの試料化合物の構造と炭化水素生成物の分布の関連性を調べた.また,粉末炭素の添加の有無,レーザー出力,レーザー発振様式の違いなどの分解条件が分解パターンに及ぼす影響について検討した.粉末炭素を混合した試料をノーマルレーザーの非集束光で分解すると,ゆるやかな条件下で急速に分解が進み,有用なパイログラムが得られる.また,この条件下では炭素が反応に関与する証拠も認められない.この方法でセミカルバゾンを分解すると,もとの炭素骨格を完全に保持したアルケンが多量に生成する.もとのカルボニル基の位置もこのアルケンの二重結合の位置から推定できる.低級炭化水素の分布も試料化合物の構造と密接に関連している.