Please ask if you want to do it Vitamin C +Collagen Serum by adjusting the formula Vitamin C your serum C7 give the ratio as below, will you be able to do this? WATER + สารกันเสีย 0.5% 44.1 Ferulic Acid 1.0 Collagen 4.0 Triethanolamine 99% 2.5 WaterLock 1.0 Ethoxydiglycol 20.0 Propylene Glycol 10.0 ...