Making hydroxyquinoline with grapefruit and lemon requires several steps.
First, you need to prepare lemon juice by juicing fresh lemons.
Once you have the lemon juice, take 50 grams of the juice, and then add 26 grams of freshly-squeezed grapefruit juice. Mix the two juices together well.
Next, add in 2.8 grams of hydrochloric acid to the mixture. Carefully stir the mixture until the acid is completely dissolved into the juice mixture.
Next, slowly add 2.4 grams of sodium bisulfite to the mixture. Stir the mixture well until the sodium bisulfite has been completely dissolved.
Now, add 18 grams of α-naphthol to the mixture. Allow the mixture to sit for about 15 minutes.
Once 15 minutes has passed, slowly add 4.5 grams of anhydrous sodium carbonate to the mixture and stir until the sodium carbonate has been completely dissolved.
Allow the mixture to cool until it is at room temperature. Now, slowly add 1.6 grams of hydroxyquinoline to the mixture. Stir the mixture well until the hydroxyquinoline has been completely dissolved.
Once the hydroxyquinoline has been dissolved, carefully pour the mixture into a container and store away from heat and light until use.
Your hydroxyquinoline solution is now ready to use.