And resolution in chromatography

Riley, C. M., Efficiency, retention, selectivity and resolution in chromatography, in High Performance Liquid Chromatography, Fundamental Principles and Practice (W. J. Laugh and I. W. Wainer, eds.), Blackie Academic and Professional, Glasgow, 1996, pp. 29-35. 

The effects of pH on electrokinetic velocities in micellar electrokinetic chromatography was studied by using sodium dodecyl sulfate solutions [179]. Micellar electrokinetic capillary chromatography with a sodium dodecyl sulfate pseudostationary phase has been used to determine the partition constants for nitrophenols, thiazolylazo dyes, and metal chelate compounds [180]. A similar technique was used to separate hydroquinone and some of its ether derivatives. This analysis is suitable for the determination of hydroquinone in skin-toning creams [181]. The ingredients of antipyretic analgesic preparations have also been determined by this technique [182], The addition of sodium dodecyl sulfate improves the peak shapes and resolution in chiral separations by micellar electrokinetic chromatography [183]. 

Jandera, P. and Churacek, J., Gradient elution in liquid chromatography. I. The influence of the composition of the mobile phase on the capacity ratio (retention volume, band width, and resolution) in isocratic elution — theoretical considerations, /. Chromatogr., 91, 207, 1974. 

Enantioselective separation by supercritical fluid chromatography (SFC) has been a field of great progress since the first demonstration of a chiral separation by SFC in the 1980s. The unique properties of supercritical fluids make packed column SFC the most favorable choice for fast enantiomeric separation among all of the separation techniques. In this chapter, the effect of chiral stationary phases, modifiers, and additives on enantioseparation are discussed in terms of speed and resolution in SFC. Fundamental considerations and thermodynamic aspects are also presented. 

Comprehensive 2D liquid chromatography is emerging as a new powerfnl technique for the separation of complex samples because of increased peak capacity, selectivity, and resolution in comparison to single-dimensional HPLC. 2D LC x LC systems essentially represent programming of stationary phases. Comprehensive LC x LC techniqne represents specific 2D mode, where all sample componnds eluting from the first dimension are snbjected to separation in the second dimension [167]. The whole effluent from the first dimension is transferred into the second-dimension... 

The performance of a conventional method of protein purification may generally be characterized by its capacity and resolution, in the case of a primary recovery operation the additional criteria of clarification efficiency and reduction of process volume become important parameters describing a successful procedure. In packed bed chromatography of proteins on porous adsorbents there are four main system parameters influencing the overall performance ... 

Dorsey JG. Column Theory and Resolution in Liquid Chromatography. In Meyers, RA (ed). Encyclopedia of analytical chemistry. Chichester John Wiley 8c Sons, 2000 11334-42. 

Super-resolution in chromatography is defined as the ability to detect the presence of two or more components when their mean elution tines fall within two standeurd peak widths of each other. Numerical deconvolution techniques for achieving superresolution eu e considered for the case of a single channel detector (7ZD), a multichannel detector (HS) and a two dimensional detector (video fluorometer). It is shown that the degree of ambiguity of the deconvolution decreases in going from a monochannel detector to a multicdiannel detector to a multidimensional detector. Three types of analytical situations are considered for each type of detector ... 

Figure l. A computer simulated example of the need for super-resolution in chromatography. The coa site curve, shown as a solid line, is the sum of three gaussian components occurring at time channels 45, 50 and 58,... 

Temperature has only a small effect on retention and resolution in liquid chromatography, since the enthalpy of solution from the mobile phase to the stationary phase is quite small unlike it is the case for gas chromatography. Thus analysis by liquid chromatography is most often carried out at room or relatively low temperature. 

The most obvious sources of error in analyses are related to insufficient extraction, low and irreproducible recoveries, insufficient peak resolution in chromatography, and the transformation of mercury species that may lead to artifacts. In the case of solubilized samples such as fish and mussels, speciation analysis was generally successful. However, with solids, techniques to remove or solubilize MeHg are complicated to validate by using spiking or tracer approaches, as it is difficult to prove that complete extrac-tion/separation has been achieved. A classical example of this difficulty is speciation of MeHg in sediments and soils. The only feasible approach adopted in certification of MeHg is to use different analytical approaches - that is, various extraction/sep-aration schemes and detection methods... 

Traditional procedures of detecting oligomers contained in polymer samples are based on gas, liquid, and size exclusion chromatography (SEC), combined with several structure identification methods. These techniques are indeed powerful, but sometimes low volatility of samples, low solubility in suitable organic solvent, or low resolution in chromatography make alternative and rapid methods of detection and direct identification of mixtures highly desirable. 

Source From Sample volume and resolution in analyftical countercurrent chromatography, in Proceedings of the Pittsburgh Conference. ... 

Wilsch, A. and Schneider, G.M. (1986) Retention and resolution in density-programmed supercritical fluid chromatography (Part I), J. Chromatogr. 357, 239-252. 

Thus resolution in chromatography is a function of three factors selectivity (S), efficiency ( ), and capacity (C) ... 

It is well known that a chiral environment is essential for enantiomeric resolution in chromatography, and this is also true in the case of chiral CE. In CE, this chiral situation is provided by the chiral compound used in the BGE, which is called a chiral selector or a chiral BGE additive. Basically, the chiral recognition mechanisms in CE are similar to those in chromatography using a chiral mobile phase additive mode, except that in the case of CE the resolution occurs through the different migration velocities of the diastereoisomeric complexes. Chiral resolution takes place due to the formation of diastereomeric complexes between the enantiomers of the pollutants and the chiral selector, and this depends on the type and nature of the chiral selectors used and the pollutants. 

S. P. Radko and A. Chrambach. Capillary zone electrophoresis of rigid submicron size particles in polyacrylamide solution. Selectivity, peak spreading and resolution. J. Chromatography A, 848 (1999), 443-455. 

Three general methods exist for the resolution of enantiomers by Hquid chromatography (qv) (47,48). Conversion of the enantiomers to diastereomers and subsequent column chromatography on an achiral stationary phase with an achiral eluant represents a classical method of resolution (49). Diastereomeric derivatization is problematic in that conversion back to the desired enantiomers can result in partial racemization. For example, (lR,23, 5R)-menthol (R)-mandelate (31) is readily separated from its diastereomer but ester hydrolysis under numerous reaction conditions produces (R)-(-)-mandehc acid (32) which is contaminated with (3)-(+)-mandehc acid (33). 

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