I am working out of my paper now. This is about characterization of modified Ca-alginate-chitosan-1,5-diphenylcarbazide resin for chromium(vi) as column packing material for preconcentration. Optimized pH and capacity of retention have been figured out. But to be regenerated, this resin need a suitable eluent. I've tried hydrochoric acid, sulfuric acid, nitric acid 1M,and also acidified ethanol,but those didn't work out. What do you think I should do with this?