Separation of common nucleotides, mono-, di- and triphosphates, by capillary electrophoresis

A capillary electrophoretic procedure for the separation of eleven nucleotides, 5'-mono-, di- and triphosphates of adenosine, guanosine, cytidine and uridine, has been developed. All eleven analytes can be separated in a fused-silica capillary (63 cm to the detector, I.D. 75 microns) at 20 kV in a 0.02 mol 1(-1) phosphate-borate buffer (pH 8.0-9.0) with a separation factor > or = 1. The values of the Offord parameter calculated for individual nucleotides predict that monophosphates will migrate faster than triphosphates, and in turn triphosphates will precede diphosphates. By analogy, faster electroosmotic mobility (lower electromigration) of purine nucleotides (AP, GP) can be explained by a more voluminous structure of purine derivatives (two aromatic rings as compared to pyrimidines). Generally speaking, all compounds separated follow the Offord equation assuming that the triphosphate derivatives are ionized to the third degree forming HL(3-) anions. This assumption is in agreement with the current knowledge about protolytic equilibria of polyphosphates. The only exception to this rule is faster migration of guanosine-5'-triphosphate (GTP) preceding uridine-5'-monophosphate (UMP) which is ascribed in part to the larger molecule of GTP and the two additional OH-groups bound to the pyrimidine ring of UMP.