Other Partition Chromatography

Paper chromatography is only applicable on a micro scale and several attempts have been made to extend it to a larger scale. Mitchell and Haskins (1949) have described a chromatopile for such fractionations. This consists of a pile of filterpapers which are used as the column. Jones (1949) suggests the use of thick paper which may best be run by ascending chromatography. Recently there has become available preparations of powdered cellulose which are suitable for use in columns. 

Diatomaceous earth (Kieselguhr) may be used as an inert support for the aqueous phase of a partition chromatogram (Martin, 1949a Bell et al., 1949). Being only a very weak adsorbent, it is likely to be useful for larger peptides which may tail badly on other chromatograms due to excessive adsorption. 

Certain hydrophobic peptides are difficult to fractionate as they all tend to run fast on the usual chromatograms in which water is the stationary phase (Synge, 1949). Recently systems have been described using adsorbents such as rubber, in which an organic solvent is held as the stationary phase and the column is developed with water or a buffer solution (Boldingh, 1948 Howard and Martin, 1950). 

---

Other modes of LC operation include liquid-liquid partition chromatography (LLC) and bonded phase chromatography. In the former, a stationary liquid phase which is immiscible with the mobile phase is coated on a porous support, with separation based on partition equilibrium differences of components between the two liquid phases. This mode offers an alternative to ion exchange in the fractionation of polar, water soluble substances. While quite useful, the danger exists in LLC that the stationary phase can be stripped from the column, if proper precautions are not taken. Hence, it is typical to pre-equil-ibrate carefully the mobile and stationary phases and to use a forecolimn, heavily loaded with stationary phase 9). 

A procedure for the determination of 7-benzene hexa-chloride and DDT in benzene hexachloride-DDT-sul-fur formulations, employing partition chromatography, is described. The procedure has also been applied to the assay of 1,1,1 -trichloro-2,2-bis(p-methoxyphenyl)-ethane in technical methoxychlor. Results of separation of other insecticidal ingredients are discussed. 

On the basis of results reported in this paper, it would appear that partition chromatography will find other applications in analysis of insecticide formulations. The method possesses a certain degree of specificity in that the partition behavior of the compounds being studied is a characteristic property. 

The most popular and versatile bonded phase is octadecylsilane (ODS), n-C18H37, a grouping that is non-polar and used for reverse phase separations. Octylsilane, with its shorter chain length, permits faster diffusion of solutes and this results in improved peak symmetry. Other groups are attached to provide polar phases and hence perform normal phase separations. These include cyano, ether, amine and diol groups, which offer a wide range of polarities. When bonded stationary phases are used, the clear distinction between adsorption and partition chromatography is lost and the principles of separation are far more complex. 

The liquid liquid partition chromatography (LLPQ method involves a stationary liquid phase that is more or less immobilized on a solid support, and a mobile liquid phase. The analyte is therefore distributed between the two liquid phases. In conventional LLPC systems, the stationary liquid phase is usually a polar solvent and the mobile liquid phase is an essentially water-immiscible organic solvent. On the other hand, in reversed-phase chromatography (RPQ, the stationary liquid is usually a hydrophobic... 

The term plate height comes from distillation theory. Some high-performance distillation columns contain discrete units called plates, in which liquid and vapor equilibrate with each other. As a teenager, A. J. R Martin, coinventor of partition chromatography, built distillation columns in discrete sections from coffee cans. (We don t know what he was distilling ) When he formulated the theory of partition chromatography, he adopted terms from distillation theory. 

The concept of plate theory was originally proposed for the performance of distillation columns (12). However, Martin and Synge (13) first applied the plate theory to partition chromatography. The theory assumes that the column is divided into a number of zones called theoretical plates. One determines the zone thickness or height equivalent to a theoretical plate (HETP) by assuming that there is perfect equilibrium between the gas and liquid phases within each plate. The resulting behavior of the plate column is calculated on the assumption that the distribution coefficient remains unaffected by the presence of other... 

Other applications besides purification of biomolecules are affinity partitioning (Labrou, 1994), extractive bioconversions (Andersson, 1990 Kaul, 1991 Zijlstra, 1998), liquid-liquid partition chromatography, and analytical assays. Although industrial applications of aqueous two-phase systems have not gained widespread use to date, practical and economic feasibility has been proved (Tjemeld, 1990 Cunha, 2002). 

An extraction, ion-pair partition chromatography separation method was developed by Borg and Mikaelsson for pentazocine using fluorescence detection (25) and has been used by others (57.58). 

The compatibility of electrochemical detection with the various modes of liquid chromatography is limited. For all practical purposes, electrochemical detection is not suitable for use with normal phase adsorption or partition chromatography due to the solvents of low dielectric constant used as the mobile phase. On the other hand, reverse-phase adsorption and partition (including ion-exchange or ion-pairing systems) are highly com-... 

A direct application of paper partition chromatography to a problem of ribose chemistry was made by Barker and Lock71 who hydrolyzed tetraacetyl-di-D-ribose anhydride (p. 173) and showed by chromatography that only ribose was formed. Other applications of partition chromatography to the sugars have recently been reviewed.72 73... 

If retardation is caused by adsorption on granular solids or other fixed surfaces, the technique is called adsorption chromatography, as noted above. If the solid surfaces merely act as a scaffold to hold an absorbing liquid (which may be of a chosen polarity) in place—perhaps within the pores of solid particles—we have partition chromatography. Many cases lie between these extremes this occurs whenever the solid acts as a support for liquid but retains some adsorptive activity [7]. A special case exists with chemically-bonded phases (CBPs), which usually consist of a one-molecule thick layer of hydrocarbon (often C18) chemically bonded to the solid surface. (These nonpolar phases are frequently used for nonpolar solutes in RPLC.) Partitioning into such a thin layer is affected by the nearby surface, especially since the configuration and motion of each attached molecule is restricted by its fixed anchor to the surface [8]. 

Chromatography, as compared to other separation methods based on phase equilibrium, stems from a notoriously heterogeneous physical system. Even in partition chromatography, where supposedly partition between bulk phases is predominant, the different kinds of high-area interfaces often lead to surface effects. In the most general case, we assume that there are several mechanisms of retention, both bulk and interfacial. In this case the numerator of the last equation must be enlarged to incorporate the other mechanisms... 

---