Medium-phase liquid chromatography

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. 

The synthesis of 6-hydroxy fluvastatin with M. rammaniana DSM 62752 gave high conversion (>95 %) in shake flask culture on 400 mL scale with 0.1 g L of fluvastatin as well as on 22 L scale in a Wave bioreactor-fed batch process at a final substrate concentration of 0.4 g L Instead of the partial purification by a second solid-phase extraction described above, 6-hydroxy fluvastatin can be obtained in high purity ( 95 %) by, for example, preparative medium-pressure liquid chromatography (MPLC) on RP18 silica gel. ... 

Zogg, G.C., N dredy, Sz., and Sticher, O., Operating conditions in preparative medium pressure liquid chromatography (MPLC). II. Influence of solvent strength and flow rate of the mobile phase, capacity and dimensions of the column, J. Liq. Chromatogr., 12, 2049, 1989. 

The extreme sensitivity of the visible absorption spectrum to small changes in the surrounding medium has made this betaine dye a useful molecular probe in the study of micellar systems [298, 299, 443-445], mieroemulsions and phospholipid bilayers [299], model liquid membranes [300], polymers [301, 446], organic-inorganie polymer hybrids [447], sol-gel matrices [448], surfaee polarities [449-451], and the retention behaviour in reversed-phase liquid chromatography [302]. Using polymer membranes with embedded betaine dyes, even an optical alcohol sensor has been developed [452]. 

Part of this material (340 mg) was purified even more by reversed-phase medium-pressure liquid chromatography procedure using a column (2.5 x 45 cm) of Whatman LRP-I (C-18-bonded silica gel, 13-24 xm) eluted with a gradient from 15-60% acetonitrile in 0.1% TFA. Aliquots from the main peak were pooled and lyophilized to give 75 mg of almost pure peptide, which counted a 18.5% yield based on resin incorporation. The final purification was achieved by a preparative RP-HPLC... 

In reversed phase liquid chromatography (RPLC) silylated silicas are preferred. The surface of these silicas is covered with chemically bonded non-polar groups such as alkyl chains or polymeric layers (Chapter 3.2.3). Silica modified with medium polar groups such as cyano, diol or amino might be used in NP as well as RP mode. Alternatively, cross-linked polymers such as hydrophobic styrene divinyl benzene-copolymers can be used (Chapter 3.2.4). Polymer packings show stability in a pH range 2-14 while silica based packings show limited stability for pH > 7. 

Reversed phase liquid chromatography is used in separating polar to medium polar components. Their separation is based on the interaction of the lipophilic part of the solutes with the non-polar surface groups. Retention depends on the nature of the active groups bonded on the silica surface as well as the functional groups of the solute. The hydrophobicity of reversed phase packings differs in the relative sequence ... 

CSP = chiral stationary phase SMBC = simulated moving bed chromatography HPLC = high-performance liquid chromatography MPLC = medium pressure liquid chromatography SFC = super-critical fluid chromatography. 

Hogendoom, E. A., Huls, R., Dijkman, E., and Hoogerbmgge, R., Microwave assisted solvent extraction and coupled-column reversed-phase liquid chromatography with UV detection. Use of an anal)4ical restricted-access-medium column for the efficient multi-residue analysis of acidic pesticides in soils, J. Chromatogr. A, 938, 23-33, 2001. 

Other techniques that can be useful for the purification of protected peptide segments include normal-phase column chromatography on silica gel and medium-pressure liquid chromatography (MPLC) in both normal and reversed-phase modes [2,3]. 

Sweeteners such as saccharine, sodium cyclamate, and acesulfam-K are more and more frequently used in food industry instead of sugar or glucose syrup. These compounds in alkaline medium exist as anions, thus anion-exchange chromatography with conductivity detection provides an alternative to reversed-phase liquid chromatography (RPLC) with UV/Vis detection. ... 

Particulate sorbents are available almost exclusively in the shape of micrometersized beads. These beads are packed in columns and represent currently the most common stationary phases for high-performance liquid chromatography (HPLC). Despite their immense popularity, slow diffusional mass transfer of macromolecular solutes into the stagnant pool of the mobile phase present in the pores of the separation medium and the large void volume between the packed particles are considered to be major problems in the HPLC of macromolecules, frequently impairing their rapid and efficient separation [1]. 

Liquid-liquid chromatography in its simplest form involves two solvents that are immiscible. However, many recently developed media consist of a liquid (the stationary phase) that is firmly bound to a solid supporting medium. As a result, it is possible to use a second solvent (the mobile phase) which under normal conditions would be miscible with the first solvent. The second solvent is permitted to move in one direction across the stationary phase to facilitate the separation process. The presence of a supporting medium introduces some problems in the system and, in theory, it should be completely inert and stable, showing no interaction with the solutes in the sample. However, this is not always the case and sometimes it affects the partitioning process, resulting in impaired separation. 

Mobile phase in chromatography, the phase (gaseous or liquid) responsible for moving an introduced sample through a porous medium to separate components of interest. 

Postigo C, de Alda MIL, Barcelo D et al (2010) Analysis and occurrence of selected medium to highly polar pesticides in groundwater of Catalonia (NE Spain) an approach based on on-line solid phase extraction-liquid chromatography-electrospray-tandem mass spectrometry detection. J Hydrol 383 83-92... 

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