I have just started to prepare a PBS buffer for my experiment and I found recipes for a PBS buffer both with and without KCl. What is the difference between both of them?
PBS can refer to a variety of different solutions, which is why it would be desirable to write out the ingredients in full when writing up the method. Unfortunately, people do not always do that.
The idea behind PBS is to mimic the pH, ionic composition and ionic strength of human blood plasma, and to buffer the pH at 7.4. A common recipe includes137 mM NaCl, 10 mM Phosphate (a mixture of Na2HPO4 and KH2PO4), 2.7 mM KCl, and a pH of 7.4. Some recipes include calcium and magnesium salts.
You can see that the amount of KCl is quite low compared to the amount of NaCl, so you may leave it out or replace it with NaCl if it isn't important to your experiment to mimic the KCl content of human blood plasma.