How to prepare phosphate buffer solution (PBS) for microfluidics use?

Buffer solutions are very important in microfluidics use. In this post I will share my experience on how to prepare PBS. I have been using 100mM phosphate buffer of pH 7.4.

Chemicals Required: Sodium mono phoaphate (NaH2 PO4 H2O, FW=138), sodium diphosphate (Na2HPO4 , FW=142). For the molecular weight check the container of the chemicals.
Procedure:

1. Prepare 100mM monobasic solution: weigh appropriate monobasic and dissolve in water and make appropriate volume to make the concentration 100mM.
2. Prepare 100mM dibasic: weigh appropriate monobasic and dissolve in water and make appropriate volume to make the concentration 100mM.
3. Take 10mL of 100mM dibasic and check pH using pH meter. Add 100mM monobasic dropwise until the pH of the solution becomes 7.4 (or desired).

This method of preparaing pH gives desired pH and desired ionic strength of the buffer solution. Addition of other acid or base to get desired pH is not necessary. This method does not introduce 'other ions' in the buffer solution.