Other Chromatographic Techniques

A single report on the resolution of racemic amino acids by TLC has been recently published. The use of silica gel TLC plates impregnated with QN (0.1%), in combination with appropriate mobile phase system, gave a successful enantior-esolution of methionine, alanine, threonine, valine, leucine, and isoleucine. This method combines the simplicity ofTLC technique with a good sensitivity (0.9-3.7 pg) and enantioselectivity (e.g., for methionine, the corresponding Ry values for d- and L-enantiomers were 25 and 50, respectively) [124], 

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Application of rotating coiled columns has become attractive for preparative-scale separations of various substances from different samples (natural products, food and environmental samples) due to advantages over traditional liquid-liquid extraction methods and other chromatographic techniques. The studies mainly made during the last fifteen years have shown that using rotating coiled columns is also promising for analytical chemistry, particularly for the extraction, separation and pre-concentration of substances to be determined (analytes) before their on-line or off-line analysis by different determination techniques. 

Transfer of the optimized TLC mobile phase to other chromatographic techniques (PLC in our case)... 

One of the most crucial influencing factors in planar chromatography is the vapor space and the interactions involved. The fact that the gas phase is present, in addition to stationary and mobile phases, makes planar chromatography different from other chromatographic techniques. Owing to the characteristic of an open system the stationary, mobile, and vapor phases interact with each other until they all are in equihbrium. This equilibrium is much faster obtained if chamber saturation is employed. This is the reason for differences in separation quality when saturated and unsaturated chambers are used. However, the humidity of the ambient air can also influence the activity of the layer and, thus, separation. Especially during sample application, the equihbrium between layer activity and relative humidity of the... 

A powerful advantage of SFC is that more detectors can be interfaced with SFC than with any other chromatographic technique (Table 4.30). There are only a few detectors which operate under supercritical conditions. Consequently, as the sample is transferred from the chromatograph to the detector, it must undergo a phase change from a supercritical fluid to a liquid or gas before detection. Most detectors can be made compatible with both cSFC and pSFC if flow and pressure limits are taken into account appropriately. GC-based detectors such as FID and LC-based detectors such as UVD are the most commonly used, but the detection limits of both still need to be improved to reach sensitivity for SFC compatible with that in LC and GC. Commercial cSFC-FID became available in... 

There is a strong limitation in the concentration range due to the logarithmic relationship between transmission and concentration (optical densities reasonably to measure range from 0.1 to 1.5). Nevertheless, protein quantification by direct UV-measurement or after staining with dyes in the visible range is a very robust method and can be found, e.g., as a common detection mode in HPLC or other chromatographic techniques. 

Other chromatographic techniques that have been applied to the tetracyclines, including CTC, involve low pressure column chromatography. Ascione et al. (64) developed a semiautomated system whereby sample solutions are automatically injected onto a column of diatomaceous earth mixed with... 

The separation mechanism is quite different from other chromatographic techniques and a broader spectrum of possible impurities can be detected at the same system (e.g., inorganic small cations, anions by indirect detection, chiral separations by adding a chiral selector, proteins and peptides by adding a polymer to the separation buffer, etc.)... 

Determination of various analgesic and antipyretic pharmaceuticals on reversed phase has included not only the analysis of serum levels of aspirin, salicylic acid and salicyluric acid using acidified acetonitrile (557), or methanol (338), but also suUinpyrazone under isocratic conditions (339), and 6-chloro-a-methylcarbazole-2-acetic acid (340). The polar thiol metabolites of acetaminophen were analyzed by RPC and the method was found to be superior to other chromatographic techniques used in this analysis (341). 

Figure 1. The relationship between SEC and other chromatographic techniques. V(, is the elution volume of an excluded peak (interstitial volume), Vj is the total permeated peak volume (Vo + Vj), and Vj. is the retention volume of an adsorbed component. Reproduced with permission from reference 8. Copyright 1984, Astor Publishing Corp.

Size exclusion chromatography (SEC) separates molecules based on size in a short analysis time. Unlike other chromatographic techniques, SEC does not retain sample species in the column, the analysis time is fixed, and everything loaded onto the column elutes within a fixed time frame. The application of SEC is limited only to the solubility of the sample in a solvent. Since tetrahydrofuran (THE) is a good solvent for coal liquids, the separation of coal liquids by SEC can be easily achieved. 

CS048 Wheals, B. B. and R. N. Smith. Comparative cannabis analysis. A comparison of high-pressure liquid chromatography with other chromatographic techniques. J Chromatogr 1975 105 396-400. 

Various countercurrent chromatographic techniques have been successfully employed for the separation of flavonoids. Countercurrent chromatography is a separation technique that relies on the partition of a sample between two immiscible solvents, the relative proportions of solute passing into each of the two phases determined by the partition coefficients of the components of the solute. It is an all-liquid method that is characterized by the absence of a solid support, and thus has the following advantages over other chromatographic techniques ... 

Both small and large analytes can be determined using direct detection in lAC. Additionally it is possible to use this technique either separately or in combination with other chromatographic techniques [1]. If this technique is performed as part of HPLC system the method can be referred as high performance immunoaffinity chromatography. 

The retention equation allows us to understand the first major difference between the CCC solute retention and the retention obtained with any other chromatographic technique. Usually, in chromatography, the same solute mixture separated on the same column and using the same mobile phase produces the same chromatogram. If it is not the case, it is a sign of column wearing or problems in the hardware (pump, detector, or injector). 

HPLC has a number of advantages over other chromatographic techniques for lipids namely, (a) it can be quantitated more easily than TLC, (b) lipids that cannot be separated by GC because they would be decomposed by the high temperatures required or by the catalytic activity of the column may be analyzed using HPLC, and (c) the separated components can be collected and subjected to further analysis, e.g., by spectroscopic techniques. Examination of the literature reveals a number of points of agreement on the difficulties and present limitations of the method. 

The reader is directed to Ref. 5, which makes an interesting comparison between HPLC and other analytical methodologies for the determination of carbohydrates in foods. Additionally, notable progress has been made in the application of high-performance capillary electrophoresis (HPCE) in this field (8-11). However, given the scope of this chapter, we will focus on the advantages and drawbacks of other chromatographic techniques versus HPLC. 

Affinity chromatography is an adsorption method based on the recognition between a ligand immobilized on a solid matrix and a biomolecule to be separated. The main difference between this method and other chromatographic techniques is the high interaction specificity between molecules and stationary phase. 

Korhammer SA, Bernruether A, Hyphenation of high-performance liquid chromatography (HPLC) and other chromatographic techniques (SFC, GPC, GC, CE) with nuclear magnetic resonance (NMR) A review, J. Anal. Chem., 354 131-135, 1996. 

In the usual instance it is necessary to use more than one analytical tool for identification (and separation) of the phospholipids in a biological extract. Other chromatographic techniques of value will be discussed later. However, now it is worthwhile to describe a methodology by which a nearly quantitative... 

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