To make a 1X PBS solution dilute concentrate 20X with distilled water. Use 50mL PBS concentrate per 950mL distilled water. Measure and pour appropriate volume of 20X PBS concentrate into a mixing flask and add DI water to final volume. Stir briefly. The 1X solution should be pH 7.6±0.2. The pH of the solution may require slight adjustment. Adjust pH with 1N HCl (if pH is high) or 1N NaOH (if pH is low).