Liquid-phase chromatography

OXIDATIVE LUMINESCENCE OF UV ABSORBING CHEMICALS. APPLICATION TO THEIR DETERMINATION IN SUNSCREEN PRODUCTS BY REVERSED PHASE LIQUID CHROMATOGRAPHY WITH CHEMILUMINESCENCE... 

D. E. Martire, Unified Approach to the Theory of Chromatography Incompressible Binary Mobile Phase (Liquid Chromatography) in Theoretical Advancement in Chromatography and Related Separation Techniques (Ed. F. Dondi, G. Guiochon, IGuwer, Academic Publishers, Dordrecht, The Netherlands,(l993)261. 

J. E. MacNair, K. C. Lewis and J. W. Jorgenson, Ultraliigh-pressure reversed-phase liquid chromatography in packed capillaiy column . Anal. Chem. 69 983 (1997). 

THREE-DIMENSIONAL SIZE EXCLUSION CHROMATOGRAPHY-REVERSE PHASE LIQUID CHROMATOGRAPHY-CAPILLARY ZONE ELECTROPHORESIS... 

Figure 9.10 Three-dimensional representation of the data volume of a tryptic digest of ovalbumin. Series of planar slices through the data volume produce stacks of disks in order to show peaks. Reprinted from Analytical Chemistry, 67, A. W. Moore Jr and J. W. Jorgenson, Comprehensive three-dimensional separation of peptides using size exclusion chromatogra-phy/reversed phase liquid chromatography/optically gated capillary zone electrophoresis, pp. 3456-3463, copyright 1995, with permission from the American Chemical Society.

E. A. Hogendoom and P. van Zoonen, Coupled-column reversed-phase liquid chromatography in envhonmental analysis (review) , ]. Chromatogr. 703 149-166 (1995). 

R. J. Senorans, J. Villen, J. Tabera and M. Heiraiz, Simplex optimization of the direct analysis of free sterols in sunflower oil by on-line coupled reversed phase liquid chromatography-gas clnomatography , 7. Agric. Food Chem. 46 1022-1026 (1998). 

Figure 13.7 Selectivity effected by employing different step gradients in the coupled-column RPLC analysis of a surface water containing 0.40 p-g 1 bentazone, by using direct sample injection (2.00 ml). Clean-up volumes, (a), (c) and (d) 4.65 ml of M-1, and (b) 3.75 ml of M-1 transfer volumes, (a), (c) and (d), 0.50 ml of M-1, and (b), 0.40 ml of M-1. The displayed cliromatograms start after clean-up on the first column. Reprinted from Journal of Chromatography, A 644, E. A. Hogendoom et al, Coupled-column reversed-phase liquid chromatography-UV analyser for the determination of polar pesticides in water , pp. 307-314, copyright 1993, with permission from Elsevier Science.

On-line coupling of normal-phase liquid chromatography (NPLC) and gas chromatography is today a well developed and robust procedure and has been regularly applied to environmental analysis. When a fraction of the NPLC sample is introduced in to the GC unit, a large-volume interface (LVI) is needed but, due to the volatility of the organic solvent used in NPLC, this does not present such a great problem. 

However, for water analysis, reverse-phase liquid chromatography is more suitable but its coupling with GC has some drawbacks because of the partly aqueous effluent. Several systems have been developed (88, 89) and applied to determine pollutants in water. 

One example of normal-phase liquid chromatography coupled to gas chromatography is the determination of alkylated, oxygenated and nitrated polycyclic aromatic compounds (PACs) in urban air particulate extracts (97). Since such extracts are very complex, LC-GC is the best possible separation technique. A quartz microfibre filter retains the particulate material and supercritical fluid extraction (SPE) with CO2 and a toluene modifier extracts the organic components from the dust particles. The final extract is then dissolved in -hexane and analysed by NPLC. The transfer at 100 p.1 min of different fractions to the GC system by an on-column interface enabled many PACs to be detected by an ion-trap detector. A flame ionization detector (PID) and a 350 p.1 loop interface was used to quantify the identified compounds. The experimental conditions employed are shown in Table 13.2. 

One of the first examples of the application of reverse-phase liquid chromatography-gas chromatography for this type of analysis was applied to atrazine (98). This method used a loop-type interface. The mobile phase was the most important parameter because retention in the LC column must be sufficient (there must be a high percentage of water), although a low percentage of water is only possible when the loop-type interface is used to transfer the LC fraction. The authors solved this problem by using methanol/water (60 40) with 5% 1-propanol and a precolumn. The experimental conditions employed are shown in Table 13.2. 

Emenhiser C., Sander L.C., and Schwartz, S.J., Capability of a polymeric C30 stationary phase to resolve cis-trans carotenoid isomers in reversed-phase liquid chromatography, J. Chromatogr. A, 101, 105, 1995. 

Emenhiser, C. et al.. Separation of geometrical carotenoid isomers in biological extracts using a polymeric Cjq column in reversed-phase liquid chromatography, J. Agric. Food Chem., 44, 3887, 1996. 

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. 

P. W. High speed gradient elution reversed-phase liquid chromatography. 

The most common approaches to sulfonylurea determinations involve high-performance liquid chromatography (HPLC). The earliest reported methods utilized normal-phase liquid chromatography (LC) with photoconductivity detection this type of detector demonstrated undesirably long equilibration times and is no longer... 

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