Systems and methods for identifying DNA strand size and purifying the DNA based on strand size using electrophoresis. The methods include moving, via voltage, a plurality of DNA strands through a separation gel from an inlet of a capillary or passage to either a first outlet or a second outlet dependent on the DNA strand length. In some implementations, the system is a capillary electrophoresis system. In other implementations, the system is a microfluidic lab-on-a-chip.