Rinsing Fluid, Granulated

Principle And Interpretation

After filtration it is often necessary to rinse the membrane filter in order to remove residues of liquid sample materials. If the sample contains higher hydrocarbons such as vaseline, paraffin, etc. or fats, the use of rinse fluid is recommended. Rinsing fluid largely complies with the formulation prescribed in the recommendations of the United States Pharmacopoeia (1).

This fluid contains balanced concentrations of nutrients, which prevent the microorganisms, retained by the filter, from being exposed to physiological shock, thus being capable to grow further rapidly. The detergent polysorbate 80 ensures emulsification of carbohydrates and fats without seriously affecting the microorganisms. If the sample contains large quantities of these compounds, additional up to 9.0 g/litre of polysorbate 80 (Tween® 80) can be added in accordance with the USP recommendations before the broth is filtered. After filtering the liquid sample, rinse the filter 3 times with 100 ml portions of the membrane-filter rinse fluid, and then complete the test in the usual way.