Gluconolactone in water base product
I'm trying to form a toner with basic ingredients as: 1. Hydrosol water 2. Amino acid (about less than 5%) 3. Glycerin and pathenol (around 5% as well) 4. Preservative with Sodium benzoate & Potassium sorbate I'm aiming to get a pH of 4.5-5 and also using Gluconolactone for this function with added benefits of moisturiser and slightly exfoliating. In concentration of 10%, it was fine at first (pH, solubility); however, the mixture starts crystallising and decreasing pH value after 8 hours. I've tried to exclude amino acid, heat/ no heat water phrase and it still didn't work. I've tried with different acids in AHA group and it has been perfectly fine, this is the first time I'm trying to formulate with glucolactone. Any advise please?