Eluant carbonate hydroxide

We compared in sect. 3.1 the holdback factors for several carboxylic and aminopolycar-boxylic acids that have been (or could be) used for lanthanide separations. It is clear that among the carboxylic acid eluants, a hydroxide group on the a-carbon atom is necessary for consistent performance across the series. One might expect that the proximity of the OH group creates the possibility of simultaneous coordination of both a carboxylate oxygen and the hydroxide, thus creating a chelate complex of enhanced stability. However... 

The sensitivity increase for some selective carbohydrates that is caused by the addition of Ba(II) is shovyn in Fig. 3-171. While retention of the first three components remains practically the same vyhen adding barium acetate, a slight retention decrease is observed for fructose and sucrose. At first vievy, this seems surprising one might suppose that the complete removal of carbonate would lead to a retention increase. However, since in this case Ba(II) has been added as acetate salt, and acetate is a stronger eluant than hydroxide, even traces of acetate in the mobile phase will result in a retention decrease. The sensitivity increase is attributed by Cataldi et al. [166] to the inhibition of the gold oxide formation by alkaline-earth metals in the order Ca(II) > Sr(II) > Ba(II) which, in turn, results in an increase of the electrocatalytic activity of the electrode. 

Eluants other than carbonate/bicarbonate have also found wide application in many environmental and nonenvironmental analyses. Some common eluants are listed in Table 1.11.2. Sodium hydroxide solution has now become an eluant of choice for many ion chromatography analyses using suppressed conductivity detection. The schematic representation of the method is outlined in Figure 1.11.2. 

Anion Analysis (Figure 9.6b). For anion analysis the analogous principles apply, only now the eluant is, for example, the hydroxide or mixed carbonate/bicarbonate ion and the suppressor column a cation exchange resin in the hydrogen form, thereby suppressing conductivity by the formation of water and dissolved carbon dioxide respectively. 

There are two solutions for the problem of changes in selectivity and retention times caused by carbonate impurities when working with hydroxide eluants, especially in the lowest mmol/L concentration range. A very simple and inexpensive solution is provided by adding divalent, electroinactive cations such as Ca(II), Sr(II), or Ba(II) to the mobile phase, which improves peak symmetry for... 

As expected, the addition of barium hydroxide results in a somewhat higher retention of all components this effect is more pronounced with lactose and cellobiose. The retention increase is attributed to the complete removal of carbonate, which precipitates in the eluant reservoir as low soluble barium carbonate. The improved peak shape for ribose that Angyal [172] attributes to the complexation of sugar molecules by alkaline-earth metals, especially by Sr(II) and Ba(II), is remarkable. Sugar molecules with a six-membered ring and a sequence of an axial (ax), an equatorial (eq) and an axial (ax) hydroxide group bind alkahne-earth metals very strongly. Ribose has such a structure ... 

The enormous influence of carbonate impurities in conventionally prepared NaOH eluants on the selectivity of monosaccharide separations is demonstrated in Fig. 3-173. Without rinsing the separator column with a concentrated sodium hydroxide solution after every chromatographic run, the retention time of mannose at the 14th injection becomes identical to that of glucose in the 5th run. So far, acceptable retention time stability could only be achieved by post-chromatographic rinsing of the separator column with a more concentrated NaOH solution. This increases the analysis time per sample to about 50 minutes. 

Eluants and regenerants suitable for the analysis of organic adds when applying an AFS-2 hollow fiber membrane suppressor are listed in Table 5-2. For the analysis of borate and carbonate with an octanesulfonic acid eluant, an ammonium hydroxide solution with a concentration c = 10 mmol/L can also be used as the regenerant. 

The addition of even minute amounts of sodium carbonate has a particularly strong effect on the retenhon behavior of mulhvalent anions. The two iron cyanide complexes, Fe(CN)6 and Fe(CN)e, are a good example their separation is obtained with an eluant containing only 3 10 mol/L sodium carbonate (see Fig. 6-9), in addihon to tetrabutylammonium hydroxide and acetonitrile. Lowering the acetonitrile content in favor of sodium carbonate, the resoluhon between both signals will decrease drashcally, although the peak shape of the iron(II) complex will be significantly improved. 

In their recent publication. Tucker et al. [73] describe the analysis of iodide in ground water and soil extracts on lonPac ASH using suppressed conductivity detection and a sodium hydroxide/methanol eluant. The soil samples to be analyzed were extracted with a carbonate/bicarbonate mixture and the resulting extracts diluted with de-ionized water after membrane filtration. As expected, the minimum detection limit for iodide with suppressed conductivity detection is in the mid-pg/L range. 

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