Ethanol must be removed quantitatively before eluting with low salt buffer.
Check the pH of the elution buffer. It must be slightly alkaline ( pH 8.5).
Large DNA or high GC content fragments are adsorbed strongly to the matrix.
Elute large DNA or high GC content fragments at 55C, by warming the pH 8.5 elution buffer and the tube/cartridge assembly in a 55C water bath for 10 minutes, swirling occasionally to distribute the warm elution buffer across the matrix. Then quickly spin the warmed assembly to elute.