The agarose may melt if Helling's buffer is used at high voltage. Resolution is higher for DNA fragments greater than 4 kb when using Helling's buffer , and in the lower molecular weight DNA range when using TBE . Elution of DNA from agarose with glass beads does not work with TBE . For overnight runs, use 40 constant volts for the large 12-20 square cm gels. For critical measurements, run the gel overnight at the lower voltage.
High voltages lead to decreased resolution.
Measure agarose and dilute buffer to appropriate concentration. Boil in an Ehrlenmeyer ml flask. Insert the comb parallel to the plate's edge, with the bottom of the teeth about 2mm above the plate. Multiple combs can be used on a gel to accommodate additional samples needing only short separation distances. The thinner the comb, the higher the resolution.