Effect of Organic Modifier on Basic Analyte pA Shift

1 Effect of Organic Modifier on Basic Analyte pA Shift 

In order for proper description of the basic analyte retention versus the mobile-phase IpH, the pH shift of the aqueous portion of the mobile phase must be 

TABLE 4-11. Retention Volnme of Aniline as a Fnnction of IpH (10-50 v/v% Acetonitrile) 

TABLE 4-12. IpK, Values of Basic Conipouuds as a Fuuctiou of Acetouitrile Compositiou 

50 v/v% acetonitrile were obtained (R 0.98) (Table 4-12). The downward change in pKa as a function of the v/v% MeCN between 0 and 50 v/v% MeCN agreed well with the IpK values determined by Espinosa et al. [93] for aniline, 0.14 pKa unit decrease per 10 v/v% acetonitrile, and 4-chloro aniline 0.18 pK unit decrease per 10 v/v% acetonitrile. 

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