Reversed-phase liquid levels

Figure 13,12 Illusti ation of the clean-up method, showing the analysis of an air sample (a) with and (b) without column switching. Details of the analytical conditions are given in the text. Reprinted from Journal of Chromatography, A 697, R R. Kootsti a and H. A. Herbold, Automated solid-phase exti action and coupled-column reversed-phase liquid cltromatogra-phy for the trace-level determination of low-molecular-mass carbonyl compounds in ak , pp. 203-211, copyright 1995, with permission from Elsevier Science.

Figure 13.13 On-line trace eniicliment-RPLC-diode-aiTay detection (DAD) cliromatogram (at 230 nm) obtained from 200 ml of tap water spiked with various pesticides at levels of 1 p.g L. Reprinted from Chromatographia, 43, C. Aguilar et al., Deteimination of pesticides by on-line ti ace emicliment-reversed-phase liquid clrromatography-diode-aiTay detection and confirmation by paiticle-beam mass specti ometi y , pp. 592-598, 1996, with permission from Vieweg Publisliing.

P. R. Kootstr-a and H. A. Herbold, Automated solid-phase extraction and coupled-column reversed-phase liquid cliromatogr aphy for the trace-level determination of low-molecular-mass carbonyl compounds in ak , 7. Chromatogr. 697 203-211 (1995). 

Reversed-phase liquid chromatography shape-recognition processes are distinctly limited to describe the enhanced separation of geometric isomers or structurally related compounds that result primarily from the differences between molecular shapes rather than from additional interactions within the stationary-phase and/or silica support. For example, residual silanol activity of the base silica on nonend-capped polymeric Cis phases was found to enhance the separation of the polar carotenoids lutein and zeaxanthin [29]. In contrast, the separations of both the nonpolar carotenoid probes (a- and P-carotene and lycopene) and the SRM 869 column test mixture on endcapped and nonendcapped polymeric Cig phases exhibited no appreciable difference in retention. The nonpolar probes are subject to shape-selective interactions with the alkyl component of the stationary-phase (irrespective of endcapping), whereas the polar carotenoids containing hydroxyl moieties are subject to an additional level of retentive interactions via H-bonding with the surface silanols. Therefore, a direct comparison between the retention behavior of nonpolar and polar carotenoid solutes of similar shape and size that vary by the addition of polar substituents (e.g., dl-trans P-carotene vs. dll-trans P-cryptoxanthin) may not always be appropriate in the context of shape selectivity. 

Palego L, Marazziti D, Biondi L, Giannaccini G, Sarno N. 2000. Simultaneous plasma level analysis of clomipramine, N-desmethylclomipramine, and fluvoxamine by reversed-phase liquid chromatography. Ther Drug Monit 22(2) 190-194. 

Temperature. The adjustment of column temperature to enhance the speed of chromatographic separations in reversed phase liquid chromatography has become more common in recent years and several specifically designed column heaters are now commercially available. Although separation speeds are usually modified by manipulation of mobile phase composition, an increase in column temperature above ambient levels can provide several additional advantages. 

Abstract The use of configurational-bias Monte Carlo simulations in tbe Gibbs ensemble allows for the sampling of phenomena that occur on vastly different time and length scales. In this review, applications of this simulation approach to probe retention in gas and reversed-phase liquid chromatographic systems are discussed. These simulations provide an unprecedented view of the retention processes at the molecular-level and show excellent agreement with experimental retention data. 

H. hth, R. Tocklu, K. Welten, G. J. de Jong, U. A. Th Brinkman and R. W. Frei (1989), Trace-level determination of 3 -azido-3 -deoxythymidine in human plasma by precon-centi ation on a silver (I)-tliiol stationary phase with on-line reversed-phase liigh-perfor-mance liquid chromatography , J. Chromatogr. 491 321-330 (1989). 

Advances in understanding solute interachons in liquid-liquid systems in a nonequilibrium environment brought reversed-phase (RP)-HPLC into the forefront of lipophilicity determinahon. The development and manufacturing of rigid, reproducible and well-characterized stationary phases and columns, as well as the accessibility and high level of automation of modern HPLC systems, have made RP-HPLC the method of choice for many laboratories. 

Gennaro, M. C., Bertolo, P. L., and Marengo, E., Determination of aromatic amines at trace levels by ion interaction reagent reversed-phase high-performance liquid chromatography. Analysis of hair dyes and other water-soluble... 

Despite its potential importance, formic acid has proven difficult to quantify at submicromolar levels in non-saline water samples. Formidable analytical difficulties are associated with its detection in highly saline samples. Ion exclusion, anion exchange, and reversed-phase high performance liquid chromatography techniques based on the direct detection of formic acid in aqueous samples are prone to interferences (especially from inorganic salts) that ultimately limit the sensitivity of these methods. 

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