Zinc Sulfate Flotation

Zinc Sulfate Centrifugal Flotation

Fill a 15 ml centrifuge tube with ZnSO₄solution (1.18 specific gravity) and pour into a glass dish.
Using a tongue depressor, push the feces (2 to 3 grams, a piece the size of a grape) through the strainer into the ZnSO₄ solution in the dish.
Using a funnel, pour the ZnSO₄-fecal mixture back into the centrifuge tube.
Centrifuge for 2 min at high speed (1500 - 2000 rpm).
Using a headed-rod or loop, remove a sample from the surface of the solution and place on a microscope slide.*
Add a drop of iodine solution (to stain the cysts and ova) and a coverslip.
Examine at 10X.

*Note You may have to take several samples with the rod or loop to get enough material to examine, you want the equivalent of a large drop on the slide.)

Click here for a video demonstration of a Zinc Sulfate Float

Helpful tips

The sieve must be in the liquid in order for the feces to be passed through.
The more feces you use, the more likely you will be able to find eggs which are present in low numbers.
To increase the sensitivity: After removing the tube from the centrifuge, fill the tube with ZnSO₄ to just over the top of the tube, place a coverslip over the top of the tube and wait 5 to 10 min. Place a drop of iodine on a slide and place the coverslip onto the drop of iodine and examine at 10X. This modification also allows you to skip using the loop or headed rod to obtain your sample, and thus may be easier to do at a veterinary practice.
If the sample contains a large amount of fat or other material that floats in water, you may want to wash the sample before doing the flotation. To do this, start at step 1 but use water instead of ZnSO₄. When you centrifuge the water-fecal mixture the eggs ,being heavier than water, will sink but the fat and other material will float. After centrifugation pour off the supernatant, add the ZnSO₄ solution and mix well. Centrifuge as in step 4 and examine as in step 5.

Preparation of ZnSO₄ Solution

Add 386 grams of ZnSO₄ to 1 liter of water. The mixture should be checked with a hydrometer and adjusted to 1.18 sp. Gr. The ZnSO4 solution should be stored tightly capped to prevent evaporation (and the resulting change in the specific gravity of the solution).

Preparation of the Iodine Solution

Add 10 gms Potassium Iodide (KI) to 1 liter of distilled H₂O. Shake to dissolve. Add 10 gms of Iodine (I₂) to the above solution. Allow to stand over-night with stirring, at this time you may still have Iodine crystals at the bottom, this is OK, just leave them there. This solution will stain (and kill) most parasite eggs and cysts (coccidial oocysts are an exception, they do not take in the iodine).