I am starting with 1.15 ug of both vector and insert for double digestion. But after gel elution I am only able to get around 3.7 ng/ul; and 10 ng/ul for vector and insert respectively in 15ul of elution buffer. I am using HiPura Himedia quick gel purification kit. The kit is around 2-3 years old. Is the inefficiency of the kit reason for very low recovery of my plasmid and insert?