Measurement of acid dissociation constants and ionic mobilities of 3-nitro-tyrosine and 3-chloro-tyrosine by capillary zone electrophoresis.

The ionization constant (pKa) and limiting ionic mobility of 3-chlorotyrosine (CT) and 3-nitrotyrosine (NT) were determined in capillary zone electrophoresis (CZE) in a wide pH range. Measurements were carried out in a poly(ionic liquid) (PIL) modified capillary at a low pH (1.80-4.00) and a bare fused capillary at an upper pH (3.00-11.00). Electrostatic interaction between analytes and inner wall was suppressed dramatically. Furthermore, parameters usually empirically assumed were calculated from a simple theoretical model. Besides pKa and limiting ionic mobility, diameter of the hydrated ion was calculated as well. The former were inserted into the database of Peakmaster software, whose predictions led to satisfactory agreement with experimental runs.