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α-Naphthyl Acetate Esterase-90 (Capsule)

Reagent Preparation

Naphthyl Acetate solution is prepared by dissolving 1 capsule in 2 mL Ethylene Glycol Monomethyl Ether. (Prepare immediately prior to use). TRIZMAL 7.6 Buffer solution is prepared by diluting 1 part concentrate with 9 parts deionized water. Citrate Dilute solution is prepared by diluting 1 part concentrate to 9 parts deionized water. Citrate-Acetone-Methanol Fixative: Take 18 mL Citrate Dilute solution and add 27 mL Acetone, and 5 mL Methanol. Seal tightly and discard after 8 hours.


  1. Pre-warm diluted TRIZMAL 7.6 Buffer solution to 37º C.
  2. Fix slides for 1 minute in Citrate-Acetone-Methanol fixative at room temperature.
  3. Wash thoroughly in deionized water and air dry for 20 minutes.
  4. Add 1 capsule of Fast Blue RR Salt to 50 mL TRIZMAL 7.6 Dilute Buffer while stirring constantly.
  5. When salt is completely dissolved in buffer, add 2 mL α-Naphthyl Acetate solution. Continue mixing for 15-20 seconds. Do not filter.
  6. Add slides and incubate for 30 minutes at 37º C. Protect from light.
  7. Remove slides and wash in deionized water for 3 minutes.
  8. Counterstain in Mayer’s Hematoxylin (if desired) for 5-10 minutes, then wash in tap water.
  9. Air dry slides. If coverslipping is required, use only an aqueous mounting media.


This enzyme is detected primarily in monocytes, macrophages, and histiocytes. It is virtually absent in granulocytes. Monocytes will show black granulation. Lymphocytes will show some occasional activity.

α-Naphthyl Acetate Esterase-90


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