We recommend using a 500 µg column (NEB #T2050/#T2057) for the purification of 150 µg of RNA rather than 3-4 of the 50 µg columns. We would expect at least 80-90% recovery of 150 µg on the 500 µg column and it would be more cost effective than using several of the lower capacity columns. It is worth noting, however, that the 500 µg column requires a 5 minute incubation with nuclease-free water during elution, so the workflow is slightly longer.