Eluent systems

There is increasing interest in copolymer systems, which, due to their chemical heterogeneity, may require very complex eluent systems in order to dissolve the sample and ensure that the separation ensues hy a pure size exclusion mechanism. In these examples, the PLgel is also compatible with eluent systems containing mixed solvents of different polarity (including water as a cosolvent up to 10% hy volume) and in organic solvents modified with acids or bases (e.g., acetic or formic acid, triethanolamine) as it is stable in the pH range of 1-14. 

TABLE 12.8 Typical Eluent Systems for Generic Types of Water-Soluble Polymers... 

Another important parameter is the eluent composition. Binary mixtures (and obviously pure solvents) should be preferred to complex mixtures, since new systems perform an on-line analysis of the composition of binary eluents. These eluent systems allow the automatic eluent recycling, with a reduced number of controls. 

FIGURE 11.4 Video scans of Fumaria officinalis chromatogram developed on alumina layer in eluent systems (a) 10% PrOH + CHjClj (b) first development with 10% PrOH + CH2CI2 on a distance of 18 cm and second development with MeOH on a distance of 10 cm. Plates scaimed after derivatization with Dragendorff s reagent. 

Preparative planar chromatography is a very important step in the complicated procedures of isolation of group of compounds or pure substances from complex matrices. The method gives additional possibilities of using various adsorbents and eluent systems to achieve complete separation of stracmral analogs. The method also enables combining the various methods of sample application, plate development, and derivatization to achieve satisfactory separation of isolated plant extracts components. 

In addition to water, virtually any organic polar modifier may be used to control solute retention in liquid-solid chromatography. Alcohols, alkyl2aiines, acetonitrile, tetrahydrofuran and ethyl acetate in volumes of less than one percent can be incorporated into nonpolar mobile phases to control adsorbent activity. In general, column efficiency declines for alcohol-moderated eluents cogqpared to water-moderated eluent systems. Many of the problems discussed above for water-moderated eluents are true for organic-moderated eluents as well. 

Musumarra et al. [43] identified miconazole and other drugs by principal components analysis of standardized thin-layer chromatographic data in four eluent systems. The eluents, ethylacetate methanol 30% ammonium hydroxide (85 10 15), cyclohexane-toluene-diethylamine (65 25 10), ethylacetate chloroform (50 50), and acetone with the plates dipped in potassium hydroxide solution, provided a two-component model that accounts for 73% of the total variance. The scores plot allowed the restriction of the range of inquiry to a few candidates. This result is of great practical significance in analytical toxicology, especially when account is taken of the cost, the time, the analytical instrumentation and the simplicity of the calculations required by the method. 

A universal eluent system was proposed for analysis of amino acids in biological fluids by IEC on the cation exchange resin Ostion LG ANB134. A study was carried out on the effect of the carrier pH on RP-HPLC of amines, using a Cs column and octyl sulfate as ion pairing reagent. Optimal results were obtained for the analysis of catecholamines... 

In the case of a binary eluent system the dependence of the capacity factor on the volume fraction of the component with the higher elution strength (C) can be calculated by... 

Enantioseparation of nine amphetamine derivatives, methorphan, and propoxyphene was studied by comparing two different CSP typologies, a macrocyclic antibiotic CSP (vancomycin) and a native P-cyclodextrin CSP [123]. The suitability of the eluent systems to ESI interfacing was discussed, and a tandem mass spectrometric (MS/MS) detection method was developed. 

This chapter reviews the underlying principles of ion chromatography and its application in pharmaceutical analysis. It provides an overview of eluent systems, applications of gradients, electrolytic eluent generation, suppressors, and stationary phases. Applications of ion chromatography to the confirmation of counter ions, active ingredient analysis, competitive analysis and development work are discussed. 

Other eluent systems in suppressed ion chromatography are typically chosen based on specific separation requirements. For routine analysis of monovalent and divalent anions, carbonate-based eluents represent a reasonable alternative to hydroxide-based eluent systems. Carbonate eluents are simple to prepare and can be useful in cases where anion analysis is only occasionally performed. It must be kept in mind, however, that carbonate lowers the detection sensitivity for anionic species and introduces significant nonlinearity into the analysis. ... 

For ions that are UV transparent, detection is possible through the use of indirect detection. A wide variety of different eluent systems have been described in the literature. Eluents commonly used for indirect UV detection are similar to those used in non-suppressed conductivity detection phthalate and p-hydroxybenzoic acid along with other... 

Colleagues at the Forensic Explosives Laboratory have found the following procedure suitable pre-activated sfrica gel coated plates containing an ultraviolet fluorescent indicator are used. A mixed standard solution is run in one of the channels on the plate, alongside solutions of the samples and blanks. Table 1 shows the recommended eluent systems. 

Table 1 Eluent systems for thin-layer chromatography of explosives...

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