Rinsing Fluid

Composition**

Final pH ( at 25°C): 6.9±0.2

**Formula adjusted, standardized to suit performance parameters

Directions

Suspend 9 grams in 1000 ml distilled water. If desired together with up to 9 g/litre of polysorbate 80 (Tween® 80) to i.e , filter until clear. Sterilize by autoclaving at 15 lbs pressure (121°C) for 15 minutes.

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.

Quality Control

Appearance: Cream to yellow coloured homogeneous free flowing powder

Colour and Clarity of prepared medium: Yellow coloured clear solution without any precipitate

Reaction: Reaction of 0.9%w/v aqueous solution at 25°C pH : 6.9±0.2

pH: 6.70-7.10

Cultural Response

M1622: Cultural characteristics observed after an incubation at 35 -37°C for 18 - 24 hours. Recovery is carried out on Standard Nutrient Agar No.1 (M1210)

Storage and Shelf Life

Store below 30°C in tightly closed container and the prepared medium at 2-8°C. Use before expiry date on the label.

Reference

1. The United States Pharmacopoeia, 2006, USP29/NF24. The United States Pharmacopeial Convention. Rockville, MD.