The invention discloses methods, compositions and kits for stabilizing a solubilized phenyl phosphate, preferably paranitrophenyl phosphate (PNPP), using charcoal. Also disclosed are methods, compositions and kits for recycling solubilized phenyl phosphate, preferably PNPP, that has an absorbance of less than 0.1 when measured at 405 nm due to non-enzymatic hydrolysis.