所以先选DCPIP做vitamin C既indicator的~~~ chemical reaction 如下~~~ DCPIP (blue) + H+ ----------> DCPIPH (pink) DCPIPH (pink) + VitC ----------> DCPIPH2 (colourless) C6H8O6 + C12H7NCl2O2 ----------> C6H6O6 + C12H9NCl2O2