Eluents potassium hydroxide

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. 

FIGURE 13 Potassium hydroxide eluent generator schematic. 

The adoption of an eluent having a very low conductivity, which can be passed directly through the conductometric detector. Typical eluents used are benzoate, phthalate, or other aromatic acid salts, with low limiting equivalent conductances (leading to direct detection) or potassium hydroxide eluent, with high conduc-... 

Potassium hydroxide is a suitable eluent for the determination of inorganic anions with pK values above 7. Due to the high pH value in the mobile phase, even weak acids are completely dissociated and, thus, may be detected via their conductivity. However, the conductivity of the species is lower than that of the mobile phase, so that negative signals are observed for these species. This method is called indirect conductivity detection. 

Alternatively, a strongly conducting eluent may be used. In this case, elution of the solute ions is associated with a negative conductivity change. This indirect detection method is applied to the separation of anions with potassium hydroxide as the eluent [7], A corresponding chromatogram is displayed in Fig. 6-2. This indirect detection method is also utilized in the analysis of mono- and divalent cations, which are eluted by dilute nitric acid or nitric acid/ethylenediamine-mixtures. 

Figure 1.9. Schematic representation of EG40 electrolytic production of potassium hydroxide (KOH) eluent (courtesy of Dionex Corp).

With the advent of anion exchangers with an increased affinity for hydroxide and suppressors that tolerate a higher eluent concentration, the use of sodium or potassium hydroxide has become more popular. However, it is difficult to remove all of the carbonate from chemical solutions of sodium hydroxide. Electrolytic generation is now the preferred way to produce hydroxide eluents for IC. The product is almost entirely free of carbonate and the electrolytic generation provides excellent control of the concentration. Electrolytic generators are described in Chapter 1. 

Sodium or potassium hydroxide is occasionally used as eluent in nonsuppressed IC. The hydroxide ion has a high conductivity, so the conductivity falls when other anions are eluted. The reason that this eluent is not much used is that the affinity of the hydroxide ion for the exchanger is low. High concentrations of hydroxide must be used, or long elution times must be accepted. Hydroxide eluents are used for the chromatography of anions of very weak acids borate, carbonate, cyanide, silicate, sulfide. These anions cannot be detected by suppressed chromatography. 

Sometimes a dilute eluent of fixed concentration is run for a few minutes before starting the gradient. This is illustrated in Figure 6.8. A potassium hydroxide eluent was used for the first 6 min, then a gradient of increasing KOH concentration was applied... 

To a solution of the enol lactone 25 (1 mmol) in anhydrous tetrahydrofiiran (3 mL) was added the appropriate Grignard reagent (1.5 mmol) in ethereal solution at -60 °C over 30 min. After stirring at -60 °C for 1 h, the reaction mixture was poured onto saturated ammonium chloride solution, and the reaction product extracted with diethyl ether. The organic extract was washed and dried (sodium sulfate). After removal of the solvent, the residue was dissolved in 2 N methanolic potassium hydroxide solution (4 mL), and the resultant mixture heated under reflux for 1 h. The cooled mixture was neutralised with AcOH and evaporated under reduced pressure. The residue was then diluted with water and extracted with diethyl ether or dichloromethane. Chromatography of the crude product on silica gel (eluent 3 7 ethyl acetate/hexanes) afforded pure enones 26 in 20-50% yields. 

A much more elegant way to prepare hydroxide eluents has been introduced by Liu et al. [196]. The respective device was commercialized under the trade name Eluent Generator . The most important part of this module is a cartridge, in which potassium hydroxide is generated by means of electrolysis. As schematically depicted in Figure 3.200, such a cartridge consists of an electrolyte reservoir, which is filled with a concentrated KOH solution and connected to an electrolysis chamber via a stack of cation-exchange membranes. While the... 

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