Eluent aromatic bases

Indirect photometric detection was also utilized for cation determination. Fig. 6-19 illustrates the separation of sodium, ammonium, and potassium with copper sulfate as the eluent obtained by Small et al. [29]. Aromatic bases as cationic analogues to aromatic acids used in anion analysis are inappropriate as eluents for this detection method. As monovalent cations, they are already eluted by the oxonium ions. Thus, a significant absorption change is only observed when the protonated base cation contributes to the ion-exchange process. 

Table 7.2. Properties of aromatic bases as prospective eluent components.

The equivalent conductances of the aromatic bases listed in Table 7.2 are low enough for non-suppressed conductivity detection. However, the detection limits are generally lower with indirect UV detection and the resolution is often better also. In Fig. 7.8 chromatograms of the alkali metal cations are compared with direct conductivity and indirect UV absorption detection. With the aromatic base eluents Li elutes... 

P. R. Haddad and R. C. Foley, Aromatic bases as eluent components for conductivity and indirect ultraviolet detection of inorganic cations in non-suppressed ion chromatography. Anal. Chem., 61, 1435,1989. 

The separations in Figure 7.11 were performed with 15 mL of a sample containing 2 X 10 M of each sample ion. This corresponds to an absolute amount of only 0.30 nmol of each ion. The detection Umits of several inorganic ions have been calculated for aromatic bases as eluent components using a 100 mL sample. The results given in Table 7.5 show detection limits in the low ppb concentration range. Most of the detection limits were lower for indirect UV detection than for direct conductivity detection. 

Figure 13.1 A shows a conventional high performance reversed-phase separation of a three-component mixture of aromatic acid esters obtained with a standard 4.6 mm x 250 mm octadecyl column and methanol water as the eluent. From the view of chromatographic resolution and ruggedness, this is an excellent separation. However, from a practical standpoint, an assay based on this particular separation would not be satisfactory since it wastes large amounts of time between elutions of the individual components.

The primary area of application of adsorption chromatography on polar stationary phases is in the separation of nonpolar to moderately polar organic compounds. A preliminary decision on whether or not this system is adequate can be based on sample solubility in such "nonpolar" solvents as aliphatic or aromatic hydrocarbons, haloalkanes, perhaps with the addition of a few percent of esters, acetonitrile, or even alcohols. When the sample is soluble or miscible with these eluents, the use of a polar stationary phase may be the best approach to chromatographic separation. 

Polysaccharide-based CSPs are effective for chiral aromatic hydrocarbons without polar substituents (Figure 14). For example, racemates 31 were resolved on OD using hexane-2-propanol as the eluent.79 Compound 32 was not resolved with the mixture of hexane-alcohol and pure hexane, but it was completely separated on OD using... 

Chiral separation by HPLC is a practically useful method not only for determining optical purity but also for obtaining optical isomers, and numerous CSPs are presently on the market. In order to achieve the efficient resolution of chiral compounds, we have to choose a suitable chiral column and eluent. The polysaccharide-based CSPs have a high chiral recognition ability and offer a high possibility for the successful resolution of racemates including aliphatic and aromatic compounds with or without functional groups under normal and reversed-phase conditions. 

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