Mobility surfaces for field‐inversion gel electrophoresis of linear DNA

The mobility of linear DNA during field‐inversion gel electrophoresis was measured as a function of molecular weight M r , pulse time t , and field strength E. Values of M r between 48.5 and 194 kilobase pairs (kb), E from 5 to 14 V/cm and pulse times of 0.3 to 12 s were used. The data are presented as three‐dimensional surfaces of mobility: E:t for fixed M r or graphs of mobility: M r : t for fixed E. The surfaces are not smoothly increasing functions of E , M r , or t but instead show a valley with minimum mobility and a steep rise in mobility as t increases. For a field of 10 V/cm, 1 % agarose gels, and 3:1 ratio of forward: back pulse time, the forward switching time t * at which the mobility changes most rapidly is given by t * =(0.034 ± 0.003) M r for M r in kb and t * in seconds. The data and equations delineate the best conditions to achieve a particular separation.