The Formalin-Ethyl Acetate Sedimentation (also known as the Ritchie concentration method) is a widely used technique to concentrate parasite eggs, larvae, and cysts from a stool sample. The principle is based on differential sedimentation and solvent extraction. A stool sample is first emulsified in 10% formalin, which fixes and preserves the parasites. The mixture is then strained to remove large debris. Ethyl acetate (or diethyl ether) is added to the filtrate, and the tube is shaken vigorously. The ethyl acetate acts as a solvent and a flotation agent. When centrifuged, four layers form: a top layer of ethyl acetate (containing dissolved fats and debris), a plug of debris at the interface, a layer of formalin, and a sediment pellet at the bottom. Parasite stages, being heavier, are forced into the sediment pellet along with some formalin. The other layers are discarded. The sediment is then examined microscopically. This method is highly effective for recovering a wide variety of parasites, including operculated and heavy eggs that do not float well in flotation methods.

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Zambia

• loveness Phiri – 1084 pts

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