Hi, I don't know what is in them, but I always dissolve 2tsps of sugar into warm water for cut flowers, refresh this every other day also recutting flower stems for flowers that will for last weeks..... the stem 'crusts' over so you need to trim them for the flower to be able to absorb more water.
Hope this helps
Lisa x
You also need to suppress mould/bacterial growth. A common additive as well as the sugar is to add half an aspirin (whole aspirin for large vases). Some people use lemon juice but that works out more expensive.