|
The filtration of small volumes of liquid using microfilters frequently becomes a tedious operation, requiring constant attention and a long time to complete. Several procedures for small-scale filtration have been published (1). Mowery’s procedure describes filtration using a plastic syringe coupled to a filter (2). Begtrup suggests a modification to this method that facilitates the manipulation of both the solid and the filtrate liquid. Although these procedures facilitate the filtration, they both require constant supervision by the operator. Using the device shown in Figure 1, the filtration of small volumes (≤ 10 mL) of liquid can be carried out through replacement of the vacuum or manual pressure on the piston by the pressure exerted by means of a rubber band placed on the piston. Although the filtration time is similar to that employed in the manual operation, this proposed procedure is carried out in a semiautomatic way. 
Figure 1. Photograph of the microfiltration apparatus in operation.
Materials: A plastic syringe of 5–20 mL clamped vertically, several rubber bands, and microfilters (e.g., Millipore 0.45 mm). Construction and Procedure: (a) Two notches are cut into the base of the external end of the piston on opposite sides to guide the placement of the rubber band. (b) The microfilter is inserted in the syringe and the syringe is placed in the clamp. (c) The liquid to be filtered is placed inside the syringe filling approximately 2/3 of its capacity. (d) The piston is placed in the syringe and the center of the rubber band(s) is placed in the grove in the piston and the ends of the rubber band attached to the fins of the syringe. The force exerted by the piston can be controlled by folding the rubber band in the form of “8-shape”, therefore reducing its diameter. The filtrate is recovered in a glass. We have successfully obtained clear solutions, free of the particles, smaller than 0.45 mm, coming from the TLC plates and other liquid suspensions. The procedure will be excellent for low-boiling solvents. Literature Cited- Begtrup, M. J. Chem. Educ.2001,78, 543; and refs therein.
- Mowery, D. F. J. Chem. Educ.1986,63, 509.
|
