Question: how to prepare x gal?
Answer: Prepare a 20 mg/mL stock solution of X-Gal in N,N- dimethylformamide (DMF) or dimethylsulfoxide (DMSO). Sterilization is not required. Store stock solution in glass container protected from light at -20 °C. Solutions may be stored at -20 °C for 6-12 months.