I spoke with @Sidco_Cat about this at CannaCon in Seattle around 2016, completely changed the way I purge. After introducing backfill procedures I was easily able to obtain 0ppm readings for all hydrocarbons between 36-48 hours oven time. Nitrogen also dramatically reduces the amount of nucleation we saw in shatter because all of that ambient relative moisture and oxidation no longer happen every-time you break vacuum to do flips or maintenance.