The sterilization of liquids is critical to success in many culture and molecular biology applications. Autoclaving is an option, but is time consuming and certain solutions may be damaged or rendered unusable by exposure to such extreme heat. The other commonly used method for sterilization is sterile-filtering.
In the past, I have used syringe filters for sterilization of solutions in volumes of 50 ml or less. This can get messy, as it is necessary to attach the syringe to a filter, pull out the stopper, pour the liquid into the syringe and then inject the liquid through the syringe filter. If done improperly, this can cause spilling or spraying of the liquid, which can often be a health hazard in addition to being wasteful.
Millipore, well-known and frequently used in my lab and many others for their liquid-filtering systems in the 150, 250 500, and 1000 ml sizes, has heard the cry for a more effective way to filter volumes under 50 ml. The Millipore solution is the Steriflip Filter Units. These compact units consist of a filter screwed on to a 50 ml tube. The filter is threaded on both ends so one can attach the Steriflip unit to a 50 ml conical tube, then attach to the vacuum port on the filter and turn the unit upside down, quickly filtering your solution. Once filtered, just remove the filter (and conical tube) from the Millipore 50 ml tube and use the included screw cap to safely close the Millipore tube containing your filtered liquid (the rest of the unit is disposable). The need for manual liquid transfer is eliminated as are related items such as clumsy syringes and plungers. This procedure ensures sterility, while minimizing wasted time and liquid during filtration.
Steriflip Filter Units come pre-sterilized (gamma irradiated) with 0.1, 0.22, or 0.45 um filters and a filtration area of 7 cm2. They also come with 100 um pore size filters, which are non-sterile. The system is designed to be used once, but the filter can be re-used a few times without a significant decrease in flow, depending of course, on the viscosity of the liquid.
Roseanne Shoshana Greenberg
Graduate Student
Department of Ophthalmology
Mount Sinai School of Medicine