Talk:Phosphate-buffered saline

message: There appears to be a dispute as to the proper formulation of PBS. The following appears commented out in the article:<BR>
THIS RECIPE FOR PBS IS INCORRECT,  I HAVE NEVER SEEN A K AND Na ions together in a recipe.  Unfortunately, I do not have the time for any editing and correcting of the problem. This person doesn't know what they are talking about.  The recipe above refers to Dulbecco’s Phosphate buffered saline without Mg2+, Ca2+.  Their suggestion is probably for some derivative of Sorenson or Millonig PBS.  It is a completely valid protocol for PBS and IHC applications.
: This is exactly the receipt found inn "Molecular Cloning 3"Table B.7 on page B.12 - except that molecular cloning adjusts pH to pH7.4 with HCl. 
: The receipt is strange in so far, that it doesn't explicitly mention if the phosphate used is anhydrous or one of the forms containing crystal water (if would make sense to use the dihydrate, as the anhydrous form takes up water from the air over time...). 
: Probably one has to assume it's the anhydrous form - but I strongly doubt that the resulting solution has a pH of 6.8 and even more that it changes to 7.4 upon dilution. The receipt uses a ratio of 10:2 (assuming anhydrous Na2HPO4) of Na2HPO4 to KH2PO4 - equal amounts of them should result in a solution with pH=pKa=7.2  - the 10:2 ratio ensures that the resulting solution is basic (pH 8 to 9) - so that the pH can indeed be adjusted with _HCl_ to 7.4. Diluting with ultrapure water would only shift this to a pH closer to 7, but should never go from something like 6.8 to 7.4 (crossing over from acidic to basic or vice versa) - it is more likely that the pH of 6.8 is the result of using water which contains a considerable amount of CO2 taken up from the air.... Iridos (talk) 22:57, 12 May 2008 (UTC)
replies: text: Addition of more references related to the topic is required for detailed explanation about the topicSSASHWIN (talk) 21:27, 28 January 2017 (UTC)
thread_title:  Recipe 

message: " it is good practice to always measure the pH directly using a pH meter. If necessary, pH can be adjusted using hydrochloric acid or sodium hydroxide."   
Actually it is far more accurate and reproducible to trust the pH based on weight of the chemicals - consider a 1% error in the weight of one of the phosphates will result in an error of 0.004 pH units; even a 10% error in weighing (inexcusable!)  would only make a difference of 0.04 pH units- many glass-electrode pH meters drift more than that during the reading. However it is important to know the purity of the chemicals- dibasic phosphates are deliquescent. CO2 in the water should have an insignificant effect- it affects the pH of unbuffered water but not in the presence of >100 mM phosphate buffer! Eaberry (talk) 16:58, 11 January 2024 (UTC)
replies: text: However since the 10:1.8 ratio in the composition given here results in a pH well above 7.4 for any reasonable value of pKa, The recipe is obviously designed to give a higher pH and be adjusted down with HCl. Assuming a pKa of 6.9 (at 25C and this ionic strength), you would need to add 1 mM (0.97 to be precise) of HCl to reach 7.4. The same effect could be achieved without adjustment by increasing the concentrations of KH2PO4 and NaCl; and decreasing the concentration of Na2HPO4, each by 1 mM. Eaberry (talk) 17:55, 17 January 2024 (UTC)
thread_title:  To adjust pH or not?