Eluant sodium hydroxide

If necessary, adjust the pH to 8.4-8.5 using boric acid crystals or 0.1 M sodium hydroxide the pH of the eluant is critical. 

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. 

For naphthalene black there is a perfect eluant, composed of equal parts ethanol and 0.5 N sodium hydroxide. The alkaline pH and the ethanol are required to overcome adsorption of protein to paper, but as alkaline solutions of the dye are very unstable, probably due to the presence of traces of heavy metal ions, the addition of 500 mg of Com-plexon (EDTA) per liter is required (D3 Fig. 26). In this condition an alkaline solution of amido black is stable for indefinite periods of time. 

Although many columns and eluants can be used for gradient elution, the conditions used in Figs. 2.16 and 2.17 are recommended as a good starting point. The HPIC-ASSA (5 i) separator with sodium hydroxide eluant provides the optimum combination of efficiency, selectivity, and speed without an unacceptable baseline slope. If fewer ions than the 36 shown in Fig. 2.16 need to be separated, the gradient steepness can be increased to reduce the run time. 

Fig. 8.1.1. Elution of lignosulfonates on Sephadex G-75 with 0.25 M calcium chloride as eluant (upper curve). Elution of kraft lignins on Sephadex G-50 with 0.5 M sodium hydroxide as eluant (lower curve). (Forss et al. 1976)...

Nebramycins, closely related aminoglycosides produced by Streptomyces tenebrarius, have been separated on a neutral polystyrene-based column, with aqueous sodium hydroxide as eluant and... 

Dicarboxylic acids can be separated on an adsorbent consisting of a 10 3 mixture of Kieselguhr G and polyethylene glycol (mol. wt 4000) using as eluant a 90 7 3 mixture of diisopropylether, formic acid and water. Detection can be effected by the use of a 0-04% solution of bromocresol purple in 50% methanol at pH 10 (sodium hydroxide solution). The R, values obtained are given in Table 11.10. 

Because a micromembrane suppressor allows the use of a sodium hydroxide eluant at a maximiun concentration of 0.1 mol/L (100 pequiv/mL) and with a flow rate of 2 mL/min, the suppression capacity is about 200 pequiv/min. 

Reactions of this type are common on metal surfaces with a small overpotential such as platinum [81]. Hydronium or hydroxide ions formed in those reactions in combination with suitable ion-exchange membranes can be utilized for suppression [82], The first suppressor based on this principle was developed by Strong and Dasgupta [80], It housed a spiral-type double membrane having a suppression capacity high enough for sodium hydroxide eluants with a maximum concentration of 0.2 mol/L The water required for electrolysis was delivered with a peristaltic pump. 

An ion chromatographic separation of the three orthophosphate species is impossible because of these pfC equihbria. When using the relatively weak sodium hydroxide eluant, the pH value increases as the concentration increases. With a 1 mmol/L NaOH (pH 11) eluant, orthophosphate and sulfate do not elute at all, primarily because the concentration of the monovalent eluant ions is too low for divalent analyte ions to elute. Moreover, at pH 11 about 10% of the orthophosphate exist as P04 ions, which have a much longer retention time than HP04 ions. When the sodium hydroxide concentration is increased, the monovalent and divalent ions are shifted forward in retention however, orthophosphate elutes later, because the pH value and, thus, the percentage of trivalent orthophosphate ions increases with increasing sodium hydroxide concentration. 

In theory, it is possible to derive the optimal conditions for a gradient elution with a sodium hydroxide eluant from the functional dependence of log (Vms-Vd)/Vd from log R. However, as mentioned before, this applies only to simple linear gradients with the initial eluant ion concentration of zero, which is rarely used for practical purposes. Much shorter analysis times are obtained when the gradient run starts at a higher eluant ion concentration than zero. Furthermore, gradient programs with different ramps, sometimes combined with isocratic periods, have to be developed to obtain optimal selectivity and speed of analysis. A mathematical description of the retention is impossible in all these cases, because the resulting equation for the calculation of the retention volume would be far too complex. 

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. 

Reducing and non-reducing disaccharides exhibit different retention behaviors, but can be analyzed in a single run with a gradient elution technique. To reduce the analysis time, small amounts of acetic acid are added to the sodium hydroxide eluant. Figure 3-176 shows a separation of different disaccharides on a CarboPac PAl anion exchanger. 

Using anion exchange chromatography with pulsed amperometric detection, polymers up to DP70 may be analyzed. The necessary gradient elution technique is based on the combination of sodium hydroxide and sodium acetate eluants as described above. 

---