Our PBS packet and 100X Tween 20/azide package contains five packages of 10X PBS powder (each sufficient to make 1 L of buffer) and 5 vials of 100X Tween 20/azide solution (10 mL per vial). The product is designed to be rehydrated according to the label instructions and stored at 4°C. The product is designed to be used as wash, and the components can be mixed together to make a solution of PBS containing both Tween 20 and azide. It is best to mix the solutions together AFTER rehydration. The final concentration of the 1X Tween 20 is 0.05%, and the final concentration of the azide is 0.1%.