Phosphate Buffered Dilution Water with Magnesium Chloride, commonly known as Butterfield’s Buffer, is a sterile diluent used in food, dairy, and water microbiology for preparing samples prior to microbial enumeration. The phosphate buffer maintains a stable pH environment that protects microorganisms from osmotic stress during dilution procedures. The addition of magnesium chloride improves the recovery of injured or stressed microbial cells that may otherwise fail to grow after sample handling. The 99 mL bottle format is designed to simplify dilution calculations in common laboratory workflows. For example, adding 1 mL of sample to the bottle produces a 1:100 dilution, while adding 11 mL of sample results in a convenient 1:10 suspension. The formulation is widely used in regulatory and quality control laboratories.