How can chromate pigment formation be prevented during tissue processing?

• A. Running water prior to processing
• B. Fixation with Bouin’s solution
• C. Rapid dehydration in acetone
• D. Storing tissues in cold alcohols

Answer: (A)

Preventing chromate pigment during processing hinges on removing traces of picric acid from Bouin-fixed tissue. Picric acid can remain in the tissue after fixation, and when the sample proceeds through dehydration and clearing steps, it can react with chromium-containing reagents to form chromate pigments that appear as yellow-brown deposits in sections. Washing with running water leaches out this residual picric acid, greatly reducing or eliminating pigment formation later in the workflow. Bouin’s fixative promotes the issue rather than prevents it, rapid dehydration concentrates residues and can encourage pigment formation, and storing in cold alcohols does not remove picric acid.