A syringe filter is a single-use filter cartridge. It is attached to the end of a syringe for use. Syringe filters may have Luer lock fittings, though not universally so. The use of a needle is optional; where desired it may be fitted to the end of the syringe filter. A syringe filter generally consists of a plastic housing with a membrane that serves as a filter. The fluid to be purified may be cleaned by drawing it up the syringe through the filter, or by forcing the unfiltered fluid through the filter.
Forms
In scientific applications, the most common sizes available are 0.2 or 0.22 µm and 0.45 µm pores. These sizes are sufficient for HPLC use. The smallest known sterile syringe microfilter have pore sizes of 0.02 µm. Membrane diameters of 10 mm, 13 mm, 25 mm are common as well. Some syringe filters for small volumes may not resemble a wheel at all. The syringe filter body may be made of such materials as polypropylene and nylon. The filter membrane may be of PTFE, nylon, or other treated products for specific purposes. Most manufacturers publish compatibility wallcharts advising users of compatibility between their products and organic solvents or corrosive liquids.
Application
Syringe filters may be used to remove particles from a sample, prior to analysis by HPLC or other techniques involving expensive instruments. Particles easily damage an HPLC due to the narrow bore and high pressures within. Syringe filters are quite suitable for Schlenk linework, which makes extensive use of needles and syringes. Being relatively affordable, they may be used for general purpose filtration, especially of smaller volumes where losses by soaking up filter paper are significant. Syringe filters are also available for the filtration of gases, and for the removal of bacteria from a sample. Disk filters are frequently used for the onsite manufacture of parenteral drugs and sterile eye drops, in order to remove microbiological contaminations.
Filters with 0.1 µm compared with 0.2 µm pore size have enhanced bacterial removal according to one study. The solubility of diazepam, for example, is less than 1 mg/mL at 68 °F.
