I use adsorbances to wash biodiesel instead of water washing. So I need to determine soap in my biodiesel after adsorbed. But when I was titrating for base catalyst, one of my adsorbance didn't change the color of phenophthalein at all. Then I tested biodiesel with universal indicator paper, it showed that my biodiesel is an acidic (pH~5 or 6) and when I dissolved my adsorbance with deionized water, it is an acidic too (pH~3 or 4). It means my adsorbance turns biodiesel to be an acidic. If I want to compare their efficiency for soap adsorption, How can I do with my acidic biodiesel??
Pls.help me find out the answer T_T!!