A hollow pipette member open at its opposite ends contains a plug of porous, hydrophobic material force fitted between its ends to define a liquid sample chamber between the plug and one end of the tube. At least a major portion of the pores of the plug material are impregnated with particles of a liquid scavenging material which are of smaller size than the pores so as to allow gas to be drawn through the plug. The liquid sample chamber is of predetermined volume greater than the volume of liquid drawn by a suitable suction device attached to the opposite end of the tube, so that an air gap will remain between the drawn sample and the plug. Any liquid droplets vaporized and drawn into the plug member will contact the hydrophilic particles, which will expand to block passage through those pores while still permitting gas flow through other pores. If the liquid sample itself contacts the plug, enough particles will expand to completely block gas or liquid flow through the plug.