Sampling of Culture Supernatant Without Cells

Whenever the analyte of interest is soluble in the liquid phase or part of the gas phase, sample removal via a filtering device is the most reasonable solution. Filters mounted in situ are ideal provided they do not foul within an unreasonably short period. If this is the case, a filter operating in bypass must be used because this can be repeatedly exchanged with a freshly prepared one. In our experience, bypass filters should be operated with a high tangential flow, say 2 m s 1 of superficial liquid velocity. Then, a useful lifetime of a few weeks can be achieved even in cultures of filamentous organisms. 

Separation of phases by using flotation or gravitational (at 1 g) sedimentation takes too much time to be useful and, furthermore, does not permit complete phase separation. 

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