A Microscale Suction Filtration Apparatus CIeve R. Winkel Ricks College Rexburg. ID 83460 Filtering has been one of the more troublesome operations in the microscale laboratory because of transfer andfor filter losses. This is especially true when solids are recrystallized. It is a distinct advantage if samples can be weighed, heated, reacted, concentrated, agitated, centrifuged, crystallized, recrystallized, dried, and reweighed all in a single vessel. Such an apparatus is described here. The Apparatus A tube with small holes drilled through its Bakelite screw cap is used. A small filter paper is inserted into the cap and is secured when the cap is screwed on. The tube is inverted into a neoprene rubber connector and is subjected to suction. A ~ l a s t i cfunnel base directs the filtrate into an identical collecting tube that can later be used for filtering if another solid needs w be removed. When the cao on the top filter tube is loosened one quarter turn to allowair bubbles to replace the liquid lost through the filter paper, the filtration can be completed in a matter of seconds. See the figure.
,,-Bakelite Filter Paper
-"I
Neoprene Rubber
/-Suction
Construction The apparatus is made of 10-mL Kimble culture tubes and caps (Kimble #45066). Each cap can be secured for drilling by placing it over a firm-fitting aluminum rod seated in a secured base on a drill press. The holes are made with a 1116-in. bit by turning the caps after each hole. The soft rubber cap insert is removed after drilling, and the cap is sanded flat on top and halfway up the sides so that it seals better in the rubber connectors. The rubber connectors are made from #3 neoprene stoppers. Each is drilled with a 518-in. and a 19164-in. bit held in a hole in a base board. To get a smooth finish, the stoppers are held just above the surface of liquid nitrogen in a Dewar flask before drilline. The small end of each s t o ~ ~ e r is lightly sanded with a hGh speed &sk so that it wlll'&at firmlv into the suctlon tubes ~ K m b l e#46"25201501 The plastk funnel bases that are inserted into the neoprene connectors can be made by cutting down various small plastic funnels. The small 1.5-cm filter papers can be obThe assembled apparatus. tained from VWR (#28309-989). Advantages The apparatus has several advantages over other methods. Loss of crystals and time in making sample transfers are avoided. Hot and cold filtrations are done easily because the apparatus can be inverted into a temperature bath just prior to filtering. Heat and vacuum can both be applied for fast drying. No suction trap is needed to prevent back-splashing when the collecting tube sits on the spacer. No syringe needles are needed as with the assembly of suggested by Laporterie ( I ) . No centrifugation or incomplete solvent removal is involved as with the device of Duarte, et al. (2). The apparatus has been used in organic and general chemistry laboratories for almost three years a t Ricks College. For experiments where the filtrate is discarded, a
/-
Cap
Tube
/
Collecting Tube
-Rubber
Sto per (spacery
large suction flask with a larger neoprene connector is set up on each bench so that students do not need their own suction apparatus. Students are able to get higher yields in less time. Only one caution is necessary. The suction must be released slowly aRer filtration is complete to prevent the sudden burst of air from puncturing the filter paper. Students get best results when they turn the aspirator water nearly off and then slowly unscrew the filter tube to release the vacuum. Literature Cited 1.Laporterie, A J . Ckem Edue. 19@2,69,A42. 2.Dus?te, F F;MeCay, L. L.;Popp, F. D.J. Ckem Eivc 19% 69.A314.
Volume 70 Number 6 June 1993
A161
