Isomers liquid chromatographic separation

Wise, S. A. and Sander, L. C. 1985. Factors affecting the reversed-phase liquid chromatographic separation of polycyclic aromatic hydrocarbon isomers. J. High Resolut. Chromatogr. Commun. 8 248-255. 

Normal-phase liquid chromatography is thus a steric-selective separation method. The molecular properties of steric isomers are not easily obtained and the molecular properties of optical isomers estimated by computational chemical calculation are the same. Therefore, the development of prediction methods for retention times in normal-phase liquid chromatography is difficult compared with reversed-phase liquid chromatography, where the hydrophobicity of the molecule is the predominant determinant of retention differences. When the molecular structure is known, the separation conditions in normal-phase LC can be estimated from Table 1.1, and from the solvent selectivity. A small-scale thin-layer liquid chromatographic separation is often a good tool to find a suitable eluent. When a silica gel column is used, the formation of a monolayer of water on the surface of the silica gel is an important technique. A water-saturated very non-polar solvent should be used as the base solvent, such as water-saturated w-hexane or isooctane. 

Armstrong, D.W. and DeMond, W., Cyclodextrin bonded phases for the liquid chromatographic separation of optical, geometrical, and structural isomers, J. Chromatogr. Sci., 22, 411, 1984. 

GAS Ansari. High-performance liquid chromatographic separation of the isomers of butylated hydroxyanisole. J Chromatogr 262 393-396, 1983. 

Armstrong, D.W., DeMond, W., Alak, A., Hinze, W.L., Riehl, T.E., and Bui, K.H., Liquid chromatographic separation of diastereomers and structural isomers on cyclodextrin-bonded phases, Anal. Chem., 57, 234, 1985. 

Chang, C.A., Wu, Q., and Tan, L., Normal-phase high-performance liquid chromatographic separations of positional isomers of substituted benzoic acids with amine and P-cyclodextrin bonded-phase columns, J. Chromatogr., 361, 199, 1986. 

Audebert,R. J. Liq. Chromatogr., Special Issues on Liquid Chromatographic Separation of Enantiomers, Diastereomers, and Configurational Isomers, Marcel Dekker, New York 1979 2, 1063. 

Brando, C., Hoffman, T. and Bonvini, E. (1 990) High-performance liquid chromatographic separation of inositol phosphate isomers employing a reversed-phase column and a micellar mobile phase. Journal of Chromatography B 529, 65-80. 

Jacob, K Sommer, W. Meyer, HD. Vogt, W. Ion-pair high-performance liquid chromatographic separation of porphyrin isomers. /. Chromatogr. 1985 349 283-293. 

Sehat, N., Yurawecz, M.P., Roach, J.A.G., Mossoba, MM., Kramer, JX.G., and Ku, Y. (1998) Silver-Ion High-Perfonnance Liquid Chromatographic Separation and Identification of Conjugated Linoleic Acid Isomers. Lipids 33,217-221. 

J. E. Drouin, Optimization of the mobile phase for the liquid chromatographic separation of Modalinil optical isomers on a CHIRAL-AGP column, J. Chromatogr., 605(1992)19. 

D.W. Armstrong and W. DeMond, Cyclodextrin Bonded Phases for the Liquid Chromatographic Separation of Optical, Geometrical, and Structural Isomers, J. Chromatog. Sci., 22(1984)411. 

D.W. Armstrong, W. DeMond, A. Alak, W.L. Hinze, T.E. Riehl and K.H. Bui, Liquid Chromatographic Separation of Diastereomers and Structural Isomers on Cyclodextrin- Bonded Phases,... 

C.A. Chang, Q. Wu and L. Tan, Normal Phase High Performance Liquid Chromatographic Separations of Positional Isomers of Substituted Benzoic Acids with Amine and P-Cyclodextrin Bonded Phase Columns, J. Chromatogr., 361(1986)199. 

C.A. Chang and Q. Wu, Facile Liquid Chromatographic Separation of Positional Isomers with a y-Cyclodextrin Bonded Phase Column, J. Liq. Chromatogr., 10(7)(1987)1359. 

C.A. Chang and Q. Wu, Comparison of Liquid Chromatographic Separations of Geometrical Isomers of Substituted Phenols with P- and y- Cyclodextrin Bonded Phases, Anal. Chim. Acta, 189 (1986)293. 

F.C. Marziani and W.R. Sisco, Liquid Chromatographic Separation of Positional Isomers of Suprofen on a Cyclodextrin Bonded Phase, /. Chromatogr., 465(1989)422. 

Sehat, N., M.R Yurawecz, J.A.G. Roach, M.M. Mossoba, J.K.G. Kramer, and Y. Ku. Silver-Ion High-Performance Liquid Chromatographic Separation and Identification of Conjugated LinoleicAcid Isomers. j j 33 217-221 (1998). 

Liquid Chromatographic Separation of Conjugated Linoleic Acid Isomers, and Other Fatty Acids, after Conversion to p-methoxyphenacyl Derivatives,... 

Cyclodextrins have previously been successfully employed in separation science. For instance, the partial separation and enrichment of optical and structural isomers as well as routine compounds based on selective precipitation with CDs have been reported [5,7-8]. Additionally, solutions of CDs have served as the mobile phase in a few thin-layer and high performance liquid chromatographic separations [5,9,10]. However, their most widespread application in chromatography has been as part of the stationary phase [5,6]. Various polymeric CD materials, CD gels or resins, as well as CD coated columns have been utilized as the stationary phases in the separation of many important classes of compounds [5,6,11-13]. Unfortunately, the use of these CD phases has been largely restricted to column or gas chromatography due to their low efficiency and/or poor mechanical strength [14-16]. 

Nikolova-Damyanova, B., Momchilova, S., and Christie, W.W. (2000) Silver Ion High-Performance Liquid Chromatographic Separation of Conjugated Linoleic Acid Isomers, and Other Fatty Acids, After Conversion to p-Methoxyphenacyl Derivatives, J. High Resolut. Chromatogr. 23, 348-352. 

Munteanu, D., Isfan, A., and Bratu, D., High-performance liquid chromatographic separation of BisGMA oligomers and isomers in dental restorative materials, Chro-matographia, 23, 412, 1987. 

The number of possible isomers increases with the higher C number, but more difficult separation problems associated with the volatile aromatics themselves do not arise until the range of naphthalene homologues is attained. More frequently, selective stationary phases have been proposed for the gas-liquid chromatographic separation of the isomeric dimethyl naphthalenes. Nematic crystal phases [in particular 4-(2,2-ethoxy-ethoxy-carbethoxyoxy)-cinnamic acid ester of the 4-hydroxy-4 -methoxy azobenzene] [55] or calcium chloride [56] are interesting suggestions. Calcium chloride is used with chromosorb as the support, and operations are carried out under conditions of gas-solid chromatography in packed columns. 

The most significant differences (i.e. independence) in the analytical methods are provided in the final chromatographic separation and detection step using GC/ MS and LC-FL. GC and reversed-phase LG provide significantly different separation mechanisms for PAHs and thus provide the independence required in the separation. The use of mass spectrometry (MS) for the GC detection and fluorescence spectroscopy for the LG detection provide further independence in the methods, e.g. MS can not differentiate among PAH isomers whereas fluorescence spectroscopy often can. For the GC/MS analyses the 5% phenyl methylpolysiloxane phase has been a commonly used phase for the separation of PAHs however, several important PAH isomers are not completely resolved on this phase, i.e. chrysene and triphenylene, benzo[b]fluoranthene and benzofjjfluoranthene, and diben-z[o,h]anthracene and dibenz[a,c]anthracene. To achieve separation of these isomers, GC/MS analyses were also performed using two other phases with different selectivity, a 50% phenyl methylpolysiloxane phase and a smectic liquid crystalline phase. 

---