Resorcinol Reagent

To 80 mL of hydrochloric acid add 10 mL of a 2% w/v solution of resorcinol and 0.25 mL of a 2.5% w/v solution of copper(ii) sulfate and dilute to 100 mL with water. Prepare the solution at least 4 hours before use.

Store at 2° to 8° and use within 1 week.