In the Laboratory edited by
The Microscale Laboratory
Arden P. Zipp SUNY-Cortland Cortland, NY 13045
Small-Scale Filtration Using a Modified Plastic Syringe Mikael Begtrup Department of Medicinal Chemistry, Royal Danish School of Pharmacy, Universitetsparken 2, DK-2100 Copenhagen, Denmark;
[email protected] Efficient small-scale filtration using vacuum or pressure down to the filter cake. The filter cake is pressed with the is frequently not feasible in student labs owing to inaccessipiston. Then the piston is withdrawn from the syringe (slowly bility of sources of vacuum, pressure, or centrifuges. Several until the hole is reached). This leaves the filter cake between procedures for small-scale filtration have been described (1–5). two pieces of filter paper. Solvent staying in the outlet can Mowery’s procedure (1) describes filtration in a plastic syringe be sucked away with a small piece of filter paper. using the piston for pressing the solvent through a filter in The filter cake is cautiously pushed from the syringe with the bottom of the syringe. However, when withdrawing the a straightened-out metal paper clip introduced through the piston it is difficult to maintain the position of the solid. outlet of the syringe. The solid material is then removed from Therefore subsequent washing, extraction, or drying using the syringe, if possible as a coherent plug. The residue can repeated piston movements becomes delicate. Below is described be collected on a piece of filter paper for drying by using a a simple procedure for pressure filtration that does not require small metal spatula. Filter paper from the filtration can be pumps. Both filtrate and residue can be collected. The filtration fixed with the paper clip tip while adherent solid is removed is performed in a commercially available, inexpensive plastic with the spatula. A pair of tweezers can be helpful during syringe, which is slightly modified to allow unproblematic these manipulations. repeated piston movements. The system is illustrated in Figure 1. Note The piston of a 10-mL standard medical syringe made 1. Porous polypropylene is available in discs of different diof polypropylene is drawn out. A 3-mm hole is drilled at the ameters or the disc can be punched out from a sheet of porous 5.5-mL mark of the syringe. In syringes whose outlet is not polypropylene using a hollow punch. placed at the center, the hole is best placed opposite to the outlet. A piece of filter paper is cut along a small circular disc Literature Cited such as a coin so that the paper fits snugly in the syringe. The filter paper is pressed down to the bottom with the pis1. Mowery, D. F. J. Chem. Educ. 1986, 63, 509. ton. Optionally, a disc of porous polypropylene that fits 2. Belletire, J. L.; Mahmoodi, N. O. J. Chem. Educ. 1989, 66, 964. loosely in the syringe is placed below the piece of filter paper.1 3. Duarte, F. F.; McCoy, L. L.; Popp, F. D. J. Chem. Educ. 1992, The mixture to be filtered is preferentially applied when 69, A314. the piston is removed, but fine suspensions can be introduced 4. Laporterie, A. J. Chem. Educ. 1992, 69, A42. through the hole with a Pasteur pipet. Droplets of solvent 5. Rothchild, R. J. Chem. Educ. 1990, 67, 425. can be moved downward to the suspension by tapping the syringe against the bench. The piston is placed in the syringe Piston and pressed down while closing the hole with a finger so as to cause the solSyringe vent to pass through the filter. The Hole pressing is stopped when the piston Suspension reaches the hole. The finger is removed Residue Filter paper from the hole and the piston is withdrawn to the top position. The pressing cycle can be repeated a couple of times 1 Fill the syringe 3 Stop before 4 Open hole and 5 Repeat steps 8 Push filter cake withdraw piston until the filter cake looks dry. Rememout with stretched 2–4 a couple from above with passing the of times paper clip suspension to hole ber: Close the hole when the piston is be filtered. The 6 Remove piston moved down; open the hole when the pissyringe can be and place filter filled to the ton is moved up. paper on top of hole. Replace If necessary, the filter cake can be the filter cake piston. washed and the washing solution re7 Press piston 2 Close hole and moved using similar pressing cycles. against filter press piston for cake Finally, the piston is drawn out. A filtration filter paper fitting the syringe is then pressed with the piston all the way Figure 1. Microfiltration in plastic syringe. JChemEd.chem.wisc.edu • Vol. 78 No. 4 April 2001 • Journal of Chemical Education
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