How can I improve ligation efficiency of DNA from a QIAEX II Gel Extraction Kit?
FAQ ID -141

Assuming that the ligation conditions are correct, QIAEX II particle carryover may affect ligation efficiency. Under low salt conditions, enzymes may bind to QIAEX II particles, thus reducing enzymatic activity in the ligation reaction. To remove the particles, centrifuge the tube containing the DNA for 30 seconds before pipetting the DNA.