Talk:Phosphate buffered saline

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Why is PBS used instead of ordinary saline?

When do you use PBS with calcium and magniesium, and when do you without. When we wash the cells before adding trypsin, we use PBS without magnesium and calcium, but later on we use PBS with calcium and magnesium. why is it so?

• According to the following page, Ca and Mg promote cell adhesion. Hence, the formulation contained in the article is the one that should be used when detaching cells.

Dulbecco's Media and Salts Selection Guide

• As the above comment indicates, Ca and Mg promote cell adhesion so cells are often detached from plates with a combination of Trypsin and EDTA after washing them with PBS. Since EDTA chelates metals such as Ca and Mg, adding those metals to the PBS would be counterproductive in this case. I think that Ca and Mg are more likely to be used in PBS in an in situ setting (immunohistochemistry or immunocytochemistry) and they tend to be left out in tissue culture formulations (as noted above) and in more biochemical assays where a simple buffered salt solution is needed. Matt (talk) 19:34, 5 May 2008 (UTC)

I used the think PBS was just one thing, but actually there are lots of recipes, this should be reflected in the article (will add it if I have a chance).

[edit] Recipe

There appears to be a dispute as to the proper formulation of PBS. The following appears commented out in the article:
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)