Liquid chromatographic phases

Some general considerations governing the nature of selective enantiomeric interactions for both gas and liquid chromatographic phases (at least of the bonded monomeric ligand type) have been forthcoming [721,742,754,756,781,782,790). It is generally assumed that three points of simultaneous interaction at least one of which must be stereochemically controlled, are required to distinguish the chirality of a molecule. These... 

The basic principles of fast-atom bombardment (FAB) and liquid-phase secondary ion mass spectrometry (LSIMS) are discussed only briefly here because a fuller description appears in Chapter 4. This chapter focuses on the use of FAB/LSIMS as part of an interface between a liquid chromatograph (LC) and a mass spectrometer (MS), although some theory is presented. 

The reseai ch has been carried out by the liquid chromatograph Perkin-Elmer (Series 200), which has tandem detectors the diode array (X=210 nm) and the refractometer. The temperature of a column was 30 C, speed of a mobile phase is 1.5 ml/ min. As a mobile phase, mixtures of solvents methanol - water and acetonitrile - water with addition of sodium perchlorate. The columns with the modified silica gel C8 and Cl8 (4.6x220 mm, 5 pm) were used for sepai ation of the AIST and FAS components. In order to make the identification of AIST and FAS components more reliable the ratio of the values of the above-mentioned detectors signals of each substance analyzed. 

G. R. van der Hoff, A. C. van Beuzekom, U. A. Th Brinkman, R. A. Baumann and P. van Zoonen, Determination of organochlorine compounds in fatty matrices. Application of rapid off-line normal-phase liquid chromatographic clean-up , J. Chromatogr. 754 487-496 (1996). 

Klejdus, B. et al.. Solid-phase extraction of 4(5)-methylimidazole (4-MeI) and 2-acetyl-4(5)-(l,2,3,4-tetrahydroxybutyl)-imidazole (THI) from foods and beverages with subsequent liquid chromatographic-electrospray mass spectrometric quantification, J. Sep. ScL, 29, 378, 2006. 

Epler, K.S. et al.. Evaluation of reversed-phase liquid chromatographic columns for recovery and selectivity of selected carotenoids, J. Chromatogr, 595, 89, 1992. 

Gonzales, M., Gallego, M., and Valcarcel, M., Liquid chromatographic determination of natural and synthetic colorants in lyophilized foods using an automatic sohd-phase extraction system, J. Agric. Food Chem., 51, 2121, 2003. 

Tswett s initial column liquid chromatography method was developed, tested, and applied in two parallel modes, liquid-solid adsorption and liquid-liquid partition. Adsorption ehromatography, based on a purely physical principle of adsorption, eonsiderably outperformed its partition counterpart with mechanically coated stationary phases to become the most important liquid chromatographic method. This remains true today in thin-layer chromatography (TLC), for which silica gel is by far the major stationary phase. In column chromatography, however, reversed-phase liquid ehromatography using chemically bonded stationary phases is the most popular method. 

Impregnation prior to the chromatographic development by immersing the PLC plate in a solution of the liquid stationary phase in a suitable solvent, with subsequent evaporation of the solvent. This method results in a homogeneous distribution of the liquid stationary phase all over the PLC layer. 

Radke et al. [28] described an automated medium-pressure liquid chromatograph, now commonly called the Kohnen-Willsch instrument. At present, the method is widely used to isolate different fractions of soluble organic matter (for instance, as described in Reference 29 to Reference 31). A combination of normal phase and reversed-phase liquid chromatography has been used by Garrigues et al. [32] to discriminate between different aromatic ring systems and degrees of methylamine in order to characterize thermal maturity of organic matter. 

De Jong, G. J. Optimization and characterization of silica-based reversed-phase liquid chromatographic systems for the analysis of basic pharmaceuticals./. Chromatogr. A 2000, 897,1-22. 

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. 

Wise SA, Chesisr SN, Hertz HS, Hilpert LR, and May WE (1977) A chemically bonded amino-silane stationary phase for the high-performance liquid chromatographic separation of polynuclear aromatic compounds. Anal Chem 49 2306-2310. 

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