PB Buffer (Phosphate Buffer) is a sterile, non nutritive diluent prepared according to United States Pharmacopeia standards for use in microbiological testing. This 9 mL tube format is designed specifically for the preparation of serial dilutions in pharmaceutical, cosmetic, and food microbiology laboratories. The buffer maintains a stable pH of approximately 7.2 using phosphate salts, which helps protect microbial cells from osmotic shock or pH fluctuations during sample processing. Each tube is pre filled with exactly 9 mL of buffer to allow simple preparation of a 1:10 dilution when 1 mL of sample is added. The isotonic composition preserves cell viability without promoting growth, ensuring accurate microbial counts during analytical procedures and regulatory testing protocols.