Disposable vacuum filtration apparatus capable of detecting microorganisms and particulates in liquid samples
A vacuum filtration apparatus ( 900 ) for detecting microorganisms and particulates in liquid samples. The apparatus includes a base ( 901 ), an absorbent pad ( 991 ), a filter ( 990 ), a funnel ( 930 ), and a lid ( 960 ). The funnel is releasably attached to the base, and may contain an integral flexible seal for releasably sealing the filter to the base. The outer wall of the lid may be segmented to make it flexible, this flexibility allows it to be releasably attached to the funnel or the base. The apparatus is designed so that any funnel will fit any base, and any lid will fit any base or any funnel when all parts are manufactured to normal tolerances. The apparatus may be configured to keep the filter wrinkle free in both the dry and wet states.
1. A vacuum filtration apparatus comprising:
a base including an outlet port capable of being adapted to a vacuum source, a filter seal surface disposed above said outlet port, and a pad well,
said pad well containing a substantially vertical side wall and a bottom wall, with the boundary of the top of the side wall of the pad well being coincident with the inner boundary of the filter seal surface, with the bottom wall of the pad well being substantially parallel to the filter seal surface, and disposed entirely below the filter seal surface,
an absorbent pad disposed in said pad well, with the downstream surface of said absorbent pad resting directly on the bottom wall of the pad well,
a filter means, with the downstream surface of the outer periphery of the filter means in direct contact with the filter seal surface of the base, with the outer periphery of the filter means sealed to the vacuum filtration apparatus to prevent the flow of un-filtered liquid between the filter seal surface of the base and the downstream surface of the outer periphery of the filter means, with the portion of the downstream surface of the filter means disposed inside of the filter seal surface of the base disposed above the top surface of the absorbent pad, thereby creating a gap between the portion of the downstream surface of the filter means disposed inside of the filter seal surface of the base and the top surface of the absorbent pad, when both the filter means and the absorbent pad are dry,
a funnel with an open top disposed above the filter seal surface of the base, said funnel forming a reservoir capable of holding un-filtered liquid upstream of the filter means,
with the height of the gap between the downstream surface of the dry filter means and the upstream surface of the dry absorbent pad having a value such that when a differential pressure is applied between the upstream of the filter means, after the filter means has been wetted, and the downstream of the absorbent pad, after the absorbent pad has been wetted, the differential pressure will force a central portion of the wetted filter means downward into a concave dish shape until the downstream surface of the central portion of the wetted filter means is resting flat on the upstream surface of the wetted absorbent pad, with the upstream surface of the central portion of the wetted filter means disposed below the filter seal surface of the base, with the downstream surface of the outer periphery of the wetted filter means resting on the filter seal surface of the base, and with the portion of the downstream surface of the wetted filter means between the central portion and the outer periphery substantially conforming to the side wall of the pad well of the base, so that any wrinkles caused by the swelling of the wetted filter means are removed, without causing the wetted filter means to be stretched by the differential pressure.