Reversed-phase chromatography for

Immaculada Rapado-Martinez, M., Garcia-Alvarez-Coque, C., and Villanue-va-Camanas, R.M., Performance of micellar mobile phase in reversed-phase chromatography for the analysis of pharmaceuticals containing [i-blockers and other antihypertensive drugs, Analyst, 121,1677, 1996. 

The example shown in Fig. 3.4g uses off-line column switching to combine exclusion and reverse phase chromatography for the separation of pesticides from a complex sample matrix. 

Davis, M.T., Beierle, J., Bures, E.T., McGinley, M.D., Mort, J., Robinson, J.H., Spahr, C.S., Yu, W., Luethy, R., Patterson, S.D. (2001). Automated LC-LC-MS-MS platform using binary ion-exchange and gradient reversed-phase chromatography for improved proteomic analyses. J. Chromatogr. B Biomed Sci. Appl. 752, 281-291. 

Honigberg et al (78) tested reversed-phase chromatography for separation of a number of drugs, including hydralazine. The columns contained either octadecyltrichlorosilane or diphenyldichlorosilane, bonded to 37 to 50 Jjn pellicular silica packing. Of the numerous mobile phases tested, the best for separating hydralazine, hydrochlorothiazide, and reserpine was acetonitrile/0.1% ammonium acetate (20 80), pH 7 35. The columns were 1.22 m x 2 3 mm (ID) and the flow rate was 1.4 ml per minute. Detection was by ultraviolet absorption at 25 nm. 

Figure 4.2 Protein transformations in reversed-phase chromatography for a two-state model. The native folded state can exist in either the mobile phase (Fm) or the stationary phase (Fs), as can the unfolded state (Um, Us). The equilibrium constants (k) for interconversions of the four species are indicated. (Reproduced from X.M. Lu, K. Benedek, and B.L. Karger, J. Chromatogr., 359 19 [1986]. With permission from Elsevier Science.)...

Samples of the degradant were isolated by preparative reversed-phase chromatography for structural characterization. There was sufficient sample available for the NMR measurements to be performed in a conventional 3-mm micro-NMR probe. 

Horvdth and Lipsky (29) used first this kind of reversed phase chromatography for the separation of biological compounds by HPLC and the... 

Recent advances in chromatography have made it possible to employ microbore HPLC for the determination of NOC. Its main advantage is that it uses a very low mobile-phase flow (20-100 /rl/min). This might make the TEA compatible with a reversed-phase system. Massey et al. (73), in fact, have successfully used reversed-phase chromatography for the HPLC-TEA determination of V-nitroso-V, 7V -di methylpiperazinium iodide. A 500-mm X 1-mm microbore ODS column and a mobile phase consisting of 0.1 M ammonium heptane-sulfonate in methanol water (70 30) (flow rate 20 /zl/min) was used for the HPLC separation. In another study, Riihl and Reusch (74) used a microbore Spherisorb 3 SW column for HPLC-TEA determination of volatile V-nitrosamines. The mobile phase was a mixture of 2-propanol and n-hexane (2.5 97.5). Further application of such techniques for the determination of various polar NOC, especially A-nitrosamides, in foods is desirable. 

Dieterle et al (40) used a preparative reverse-phase chromatography for separation of polar and nonpolar metabolites, including those of phenyl-... 

Isocratic elution is the most popular method for removing solutes from a column, but gradient elution is useful, especially in reversed-phase chromatography, for the removal of solutes with widely varying k values. 

Does the order of retention of the main components of the essential oils correlate with the structural differences in the main components For instance, anethole (main component in anise oil) is retained longer than is eugenol (main component in clove oil) explain this in terms of reverse-phase chromatography. If you cannot explain why the retention is as it occurs, refer to Chapter 4 and 5 or to the results of Chapter 12 (Experiment 5 Reverse-Phase Chromatography) for suggestions. 

Rs is determined by reversed-phase chromatography for each compound, and thus relative lipophilicities can be established by a very simple and convenient method [277]. 

In liquid chromatography, adjusting capacity factors is most often accomplished by changing the composition of the mobile phase. In reversed-phase chromatography, for example, decreasing the amount of organic component in the mobile phase (e.g., from 80% methanol, 20% water to 50% methanol, 50% water)... 

Selectivity The presence of organic solvent modifies mobile phase pH and equilibrium constants that affect selectivity. Changing the type of organic solvent can adjust selectivity as practiced in reversed-phase chromatography for a mixed retention mechanism. 

In summary, argentation HPLC provides a useful alternative to conventional reversed phase chromatography for the isolation and quantitation of prostaglandins. The major advantages of this technique are that it provides a better resolution of compounds which... 

A recent report recommends the use of acetone extraction followed by reversed phase chromatography for the analysis of tissue and plasma a-tocopherol levels (Zaspel and Saari-Csallany, 1983). The stationary phase was Lichrosorb RP-18 with a mobile phase of 2% water in methanol. An alternative system using a normal phase Micropak Si-5 support has also been reported to give reproducible estimations of tissue extracts of the tocopherols with a sensitivity of detection as low as 0.5-1.0 ng (Buthriss and Diplock, 1984). 

This is shown in Table VI. In the experiment with Gis-trienoic acid, on reductive ozonolysis of the C2o-polyenoic acid mixture (Fig. 6) practically the total radioactivity is locat in butanal, which represents, however, only a very minute amount of the aldehyde mixture whose main components are nonanal and hexanal. There are essentially present only polyenoic acids of the oleic and linoleic acid types. Only very small amounts of Cao-polyenoic acids of the type of the fed Cis-trienoic acid were detectable, as was mentioned. The Cao-polyenoic acid mixture has been separated into its components by reversed phase chromatography for better characterization. The radioactivity of each fraction has been... 

Pepaj, M. Wilson, S.R. Novotna, K. Lundanes, E. Greibrokk, T. Two-dimensional capillary bquid chromatography pH gradient ion-exchange and reversed-phase chromatography for rapid separation of proteins. J. Chromatogr. A, 2006,1120, 132-141. 

Currently, three modes of separation (ion, ion-pair, and reversed-phase chromatography) for the detection of sulfur(II) compounds using the iodine-azide detection system are available. 

Investigations by Mockel et al. [6] revealed that the latter may be approximately estimated in reversed-phase chromatography. For that, the capacity fectors of individual members of a homologous series are determined using two different eluent compositions, and are then plotted versus n. Since the free sorption energy becomes zero for solutes with K = 1, the phase volume ratio may be direcdy taken via Eq. (3.23) from the intersection of the two straight lines ... 

A variant of the above technique is to use a mobile phase that Itself Is chiral. This leads to the formation of a transient diastereolsomeric complex between the enantiomers md the chiral mobile phase agent. Chiral mobile phase agents that hve given good results are 10-camphorsulphonic acid, albumin, and N-benzojqrcarbonyglycyl-L-proline. It is usueil to prefer reversed phase chromatography for chiral chromatographic separations. 

Investigations by Mockel et al. [6] revealed that the latter may be approximately estimated in reversed-phase chromatography. For that, the capacity factors of individual members of a homologous series are determined using two different... 

Many small molecules of clinical interest can be detected by fluorescence. For example, porphyrins, which are intermediates in the metabolism of iron-containing heme prosthetic groups, can be detected and quantitated in urine by reversed-phase chromatography followed by fluorometric detection, exploiting the natural fluorescence of porphyrin compounds [18]. An example of reversed-phase chromatography for a mixture of carboxylated porphyrin precursors is demonstrated in Figure 21.2. The relative abundances of different porphyrin compounds can aid in diagnosing porphyria, which is a term that describes the collection of disorders caused by defects in the enzymes responsible for porphyrin metabolism. 

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