A filter device for a minute volume of liquid, usable under a centrifugal force or under pressure, comprising a cylindrical member and a hollow thread filter having an open lower end and housed in said cylindrical member to form an annular space for containing a sample liquid around the filter, with...http://www.google.ca/patents/US4690754?utm_source=gb-gplus-sharePatent US4690754 - Filter device for a minute volume of liquid
