For sampling saturated gas streams, such as those found downstream of wet scrubbers,
probes made from polypropylene, polytetrafluoroethylene (PTFE), PFA or other non-reactive
polymers may be used. Probes of this type usually incorporate a quartz-wool plug or PTFE
membrane to remove water droplets from the gas stream. Polymer probes are usable with
gas temperatures up to 90°C. If the stream is saturated and its acid dew point is greater
than 90°C, a heated metal probe at a temperature above the dew point may be used. The
temperature of the extracted gas must be maintained above the acid dew point throughout
the apparatus or at least until condensate removal stage.