First, mix said fruit juice concentrate with strong sulfuric acid to convert the sugar to carbon. Next, manually remove as much carbon as you can before a final water bath and filter off the remaining black bits. Add some baking soda to neutralize the acid. Not sure what this is gonna do to the fruit flavor though, but no matter, we're trying to get the sugar out of it. What you have left is an unknown quality of fruit flavor and sodium sulfate which you would have to remove next. That's about the extent of my scientific knowledge so after the last step you're on you're own. By the way, all this is an elaborate hoax. Do not try to make vape liquid from fruit juice concentrate. This is NOT how vape liquid is made at all. Unless you are a chemistry major with access to materials and equipment to synthesize artificial flavorings, you will not be able to make flavorings used in vape liquid and will have to purchase them from the actual companies that make them. But you gotta be 21 yrs old to buy them and I suspect that you are not. Why else would you ask a vape forum about some harebrained idea of using real fruit juice to make vape juice. I could be wrong about your age though.