Method and apparatus for directly sampling a fluid for microfiltration
Filtration cells capable of direct sampling of a fluid from a container and which may be used for microfiltration of both small and large microvolumes of a fluid to be filtered are provided. Also a process for directly transferring a fluid to be filtered from a container to a filtration cell is described. The filtration cells have one or more reservoirs and are in communication with fluid in a container to be filtered through a piercing instrument connected to a base and support for a reservoir that receives the fluid to be filtered after it passed across a filter membrane. The filtration cell may then be pressurized and vented to allow fluid to be filtered to reciprocally and tangentially pass across a filter membrane between either a container having a fluid to be filtered and a single reservoir for small volume filtrations or between two reservoirs after pressurizing a fluid to be filtered into the reservoirs from a container using a piercing instrument. Side wells for collecting samples from the bottom up from the filtration cell outlet are also provided as are a process incorporating automated equipment for transferring the container having fluid to be filtered to the piercing point for entry into the filtration cell.
1. A filtration cell capable of direct sampling of a fluid from a container, the filtration cell comprising:
(a) a reservoir to receive the fluid to be filtered,
(b) a filter membrane capable of filtering the fluid to provide a filtrate, the membrane being operatively associated with an opening in the reservoir such that fluid is able to flow over the filter membrane,
(c) a base to receive the filtrate after it passes through the membrane, the base including a path through which the filtrate is guided to an outlet from the filtration cell,
(d) a container connection supported in the filtration cell adapted to establish fluid communication between a container holding the fluid to be filtered and the reservoir, the container connection including a hollow interior in open communication with the reservoir and adapted to be in open communication with an interior of the container, and
(e) a flow channel extending between the container connection and the reservoir such that the hollow interior of the container connection is in communication with the reservoir through the flow channel, wherein the flow channel is open to the filter membrane so that fluid to be filtered can be directly passed from a fluid container over the filter membrane as it is transferred from the hollow interior of the container connection, through the flow channel and into the reservoir, the reservoir being adapted to be pressurized to direct the fluid from the reservoir back to the container.
2. The filtration cell according to claim 1 , wherein the filtration cell comprises a well to contain the filtrate to be analyzed, the well having an opening which is in fluid communication with a filtrate guide path in the base such that filtrate enters the well.
3. The filtration cell according to claim 1 , wherein the filter membrane is a microporous filter membrane.
4. A process for directly transferring fluid to be filtered from a fluid container to a filtration cell, comprising:
(a) providing a filtration cell comprising a reservoir, a filter membrane operatively associated with an opening in the reservoir, a base configured to receive filtrate passing through the membrane, the base including a path through which the filtrate is guided to an outlet from the filtration cell, a container connection adapted to establish fluid communication between a container holding the fluid to be filtered and the reservoir, the container connection including a hollow interior in fluid communication with both the reservoir and an interior of the container, and a flow channel extending between the container connection and the reservoir, the flow channel being open to the filter membrane,
(b) providing a container holding a quantity of fluid to be filtered,
(c) establishing fluid communication between an interior of the container and the reservoir with the container connection,
(d) providing an airtight connection between the reservoir and a source of air,
(e) alternately creating a pressure differential between the reservoir and the container, such that the fluid reciprocally flows across the filter membrane, and
(f) collecting the filtrate from the membrane.
5. The process according to claim 4 , further comprising optically monitoring the level of fluid in the reservoir and providing a signal indicating when the level of fluid in the reservoir exceeds a maximum or minimum level.