We fractionate samples using assymetric flow field flow (AFFFF), then test them on cells, and observed contamination of these cells on a few occasions. Deep cleaning of the AFFFF system with ethanol, detergents, acid, base, azide and antibiotics did not have a long lasting effect. Any ideas of what may be a source of persistent contamination e.g. something inside the instrument?
The fraction collector is sitting in the laminar flow, the solutions are all autoclaved and 0.1um-filtered, every measure is taken to observe sterility, however, the contamination (seen as cloudiness in cell culture media after 20-24h of incubation with cells at 37C) was also seen in a clean buffer fractionated in the system in the same manner as our samples of interest.