Anions retention factors

The approach is to measure retention times of metal cations on columns containing low-capacity resins with eluents containing perchloric acid or various perchlorate salt.s. The perchlorate anion is used to eliminate any possible complexing of a metal ion by the eluent anion. Retention factors (k) are calculated from the retention data. 

The dependence of the retention factor on weak anions from the concentration of the monoanionic mobile phase can be described by ... 

The maximum retention factor (kQ) is related to the log P value and k and k are the retention factors of the cationic and anionic forms, respectively. The pKa values are known, and the retention factor in a given eluent can therefore be predicted in reversed-phase liquid chromatography using an alkyl-bonded silica gel or polystyrene gel column. The separation conditions can be adjusted according to their logP and pKa values by the selection of a suitable organic modifier concentration and the pH of the eluent.3,4... 

Several workers have concluded that under conditions used in their study ion-pairing in the mobile phase between amphiphilic hetaeron ions and oppositely charged sample components governed retention. Horvath et al. (34) examined the effect of alkyl sulfates and other alkyl anions on the retention of catecholamines in which both the concentration and the length of the alkyl chains of the hetaerons were varied. The hyperbolic concentration dependence of the retention factor shown in Fig. 48, was found to be similar to that reported by others. 

If NaCl is replaced by the butyl-3-methyl imidazolium (BMIM) chloride IL, a 30% decrease in retention factor associated with a remarkable peak shape improvement is observed. In this case, the IL cation adsorbs on the C18 stationary phase more than Cl", thereby preventing detrimental attractive silanophilic interaction of the cationic additive. Charge-charge repulsion occurs, the retention factor is lower, and the peak shape is better. The analyte cation is largely retained by hydrophobic fast interactions. When BMIM BF4 IL replaces NaCl, both the cation and anion of the IL adsorb on the C18 surface and all the interactions cited above take place simultaneously and contradict each other. Global retention depends on the extent to which one interaction is stronger than the other [124],... 

Fig. 1.17. Dependence of retention factors, k. of guano.sine monophosphate (/). guanosine diphosphate (2) and guanosine triphosphate (.0 on the concentration.

Apart from radioactive compounds the radioactive wastes may contain non-active but chemically toxic substances. The national standards and regulations describe the discharge limits for these substances, too. Heavy metals are toxic compounds, most often present in liquid radioactive wastes. The experiments showed that most of these metals are removed by UF/complexation method. The method is inefficient for removal of monovalent ions, bivalent cations and anions are retained in 25%-50%, but high retention of the metals like Mn, Fe, Co, Cu, Pb, Cr was observed. The retention factors for those metals in two-stage experiment described above, were as follows ... 

The retention times of sample anions become longer as the operating pH becomes more acidic and the net positive charge on the ion exchanger increases. Figure 3.4 plots the retention factor as a function of eluent pH for several sample anions. Thiocyanate and molybdate are very strongly retained, even at moderately acidic pH values. 

With a 50 X 4.6 mm column packed with a polymethacrylate anion exchanger of 30 3 p/mL capacity, the chromatographic behavior of several anions was studied by direct photometric detection at 210 nm. Linear plots were obtained for log k (log retention factor) vs. log NaCl concentration in the eluent (Fig. 6.15). 

Figure 4.8 Chromatograms displaying injection peak. The injection peak is the unretained peak that allows access to retention factors. This is normally the first peak on the chromatogram. It can interfere with other early-eluting anions such as fluoride (Chromatograms from AUtech).

The following is a graph showing the retention factors as a function of concentration of perchlorate anion obtained in Figs. 5-17 to 5-19 under the three different experimental conditions. It can be seen that, regardless of pH, the counteranion concentration is the determining factor that affects the solvation and ultimately the retention of the analyte. 

Figure 5-20. Retention factor as a function of concentration of perchlorate anion on basic analyte. A pH of mobile phase adjusted with perchloric acid,...

When the retention factor is plotted against the pH (Fig. 5-22a), the increase in retention caused by the perchlorate modifier seems to be more significant. However, the graphical representation of retention factor vs concentration (Fig. 5-22b) actually defines the strength of the chaotropie anion. This observed increase in retention shows that, for similar concentrations of the counteranion of the acid, perchlorate is more... 

As can be seen from Fig. 5-30, the retention factor decreases together with the pH of the mobile phase, until pH 2.6 is reached. Then the retention factor starts to increase with the increase of the concentration of the perchlorate anion (decrease in pH). This is due to the chaotropic effect. At pHs close to the p/f of aniline (4.6), the peak shape is broad and severe fronting is observed. The increase of the perchlorate concentration at low pHs gave retention factors comparable to those at higher pH values. 

From this equation, we can see that at low pH, the retention factor of the analyte is that of the acid form and at high pH, of the anionic form. There will be a rapid transition from one retention factor to the other one when the pH is around the pK, of the acid. If the retention factor of the acid form is 0, Equation (12.23) simplifies to... 

Figure 12-3 shows the dependence of the retention factor on pH according to Equation (1Z23), assuming that the retention factor of the anionic form itself... 

Retention Factors for Anions on Ion Exchangers of Different Hydropho-... 

The effect of pH on the retention factors of solutes, eluted with an anionic surfactant, is very similar on Cl8 columns to that obtained using cyano columns, when hydrophobic interactions dominate. However, less hydro-phobic and negatively charged solutes will elute very quickly on C18 columns, because of repulsion from both micelles and negatively charged modified stationary phase. Fig. 5.11 shows plots of k vs. pH with the typical... 

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