Citric Acid is one of the more common ingredients used to give eliquids their tart flavor. Our solution of citric acid is concentrated at 10% for PG (Industry standard),and at 5% in VG (PG-free). PG can attain a max solubility of ~100mg/mL (10% solution) of citric acid, while VG can only obtain ~55mg/mL. However, ethyl alcohol is suitable for very saturated solutions of ~150mg/mL and recommended for maximum citric acid solubility as a carrier solvent. However through us in our formulations, we have found the 10% PG and 5% VG solutions to be the most stable and usable concentrations. 5% VG solutions are great for those looking to make a true 100% PG-free vape - citric acid is seemingly difficult to find in these solvents :) Recommended dilutions for final end concentrations of citric acid in eliquid are ~0.5-1mg/mL (0.05-0.1%) to start, of course adjusting for taste preference. Remember citric acid doesn’t magically "round-out" your eliquids, flavor art takes research!