Retention factor acetonitrile phosphate buffers

This has been repeatedly confirmed in several studies see, for example. Figure 4.4. Here, the retention (bars) and separation factors (lines) of tricyclic antidepressants in acidic acetonitrile/phosphate buffer are shown. In the case of quite different retention factors depending on the hydrophobic character of the phases (differently strong interactions), apart from a few exceptions very similar separation factors result. Although the analytes are retained for different lengths of time on the stationary phases, they show a similar selectivity behavior. This is observed especially with neutral or - by means of the pH-neutralized molecules. In this case, mainly hydrophobic interactions between the analytes and the surface of the material dominate. These are not especially specific the individual differences of the phases with respect to selectivity do not come into effect. 

Chem. 1 Comparison according to all retention factors in acidic/alkaline methanol/acetonitrile phosphate buffers, S2. 

Fio. 47. Retention factors of pteroyl-oliso-yL-glutamates as a ftinction of the eluent pH. The solid lines were calculated as diKussed in Bush et at. (204). Data were obtained for folic acid (FA) and oligo yglutainates containing one (Ft Glu,), three (Ft GIU ). hve (Ft GtU ), and seven (Ft Glur) utamyl residues. The data were obtained on 5 Partisil ODS-2 with 0.1 M phosphate buffers containing 696 (v/v) acetonitrile as eluent, 4S C, with detection at 254 nra. Reprinted with permission from Bush rf a/. (204). 

Inject 20 /d of solution (5). When the chromatograms are recorded under the prescribed conditions, the retention times are 5-vinyl-2-pyrro-lidone, about 18 min and vigabatrin, about 21 min. The test is not valid unless the resolution factor between the peaks corresponding to 5-vinyl-2-pyrrolidone and vigabatrin is at least 1.5 if necessary, adjust the concentration of the mobile phase (reduce the concentration of the phosphate buffer solution to increase the retention time of vigabatrin and increase the concentration of acetonitrile to decrease the retention time of 5-vinyl-2-pyrrolidone). 

Figure S-IS. Comparison of retention factors for 4-ethylpyridine as a function of pH using three different acidic modifiers. Column 150 x 4.6 mm Zorbax XDB-C18. Mobile phase acetonitrile - 10 mM. sodium phosphate buffer adjusted with trifluoroacetic acid, (10 90) flow rate 1.0 ml/min 25 C, UV 2.54 nm, sample 1 pi injection.

Fig. 8. On the bandwith of retention and separation factors by the separation of metabolites of tricyclic anti-depressants in acetonitrile/acidic phosphate buffer.

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