Talk:Phosphate-buffered saline

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Why is there a link to a particular company in the sources of the article? There are other companies that offer the same product, so it seems quite biased. — Preceding unsigned comment added by Enbaros (talk • contribs) 13:59, 21 August 2013 (UTC)

Deleted following passage: "PBS can be used as a diluent in methods to dry biomolecules, as water molecules within it will be structured around the substance (protein, for example) to be 'dried' and immobilized to a solid surface[citation needed]. The thin film of water that binds to the substance prevents denaturation or other conformational changes. Carbonate buffers may be used for the same purpose but with less effectiveness[citation needed]. PBS can be used to take a reference spectrum when measuring the protein adsorption in ellipsometry[citation needed]." This passage is misleading at best. It also very narrowly refers to certain applications taken out of context, which does not make much sense. --Xenon129 (talk) 23:35, 28 October 2011 (UTC)

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).

is pbs isotonic with human cells because article says its not isotonic and then in application it says its isotonic so plz edit — Preceding unsigned comment added by 27.106.80.242 (talk) 19:28, 2 November 2013 (UTC)

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)

Need more details on the application and introduction sections in phosphate-buffer salineSSASHWIN (talk) 21:51, 26 January 2017 (UTC) In addition to that, add more information regarding the chemical reactions involving phosphate-buffer saline which will be helpful in understanding more about the topicSSASHWIN (talk) 21:51, 26 January 2017 (UTC)

I checked the citations, all the links are working perfectly.SSASHWIN (talk) 21:55, 26 January 2017 (UTC)

Addition of more references related to the topic is required for detailed explanation about the topicSSASHWIN (talk) 21:27, 28 January 2017 (UTC)

Buffer pH is not dependent on ion concentration

"The pH of the 10x stock solution of PBS is ~6.8, but when diluted with water to 1x PBS it should change to 7.4."

This line is incorrect, surely? Buffer pH is not dependent on ion concentration, it should stay the same at 10x dilution.

The 10x stocks you can buy are all pH 7.4. https://www.thermofisher.com/order/catalog/product/AM9625 — Preceding unsigned comment added by 129.11.70.31 (talk) 15:34, 9 March 2018 (UTC)

Actually the pKa is somewhat dependent on ionic strength, because the divalent HPO4^-2 is stabilized by high ionic strength to a greater extent than the monovalent H2PO4^- is (H+ activity is measured directly, so its activity coefficient is not important). IIRC the pKa extrapolated to infinite dilution is 7.2, but at physiological ionic strength it is more like 6.8. (even pKa=6.8 would not jibe with the 10:1.8 ratio here giving 7.4, so I may recollect incorrectly)Eaberry (talk) 17:31, 11 January 2024 (UTC)

Yes- Phillips et al. 1963 (Biochm 2,501-508) determine pKa2 of phosphate as a function of temperature and ionic strength µ. They give:

at 25C: pKa2 = 7.18 - 1.52 sqrt(µ) +1.96 µ

at 37C: pKa2 = 7.15 - 1.56 sqrt(µ) + 1.22µ

The 1x solution described here has ionic strength 0.1715, which would give a pKa 6.887 at 25C, 6.713 at 37C.

There is a minimum around µ=0.15 (@25C), then it starts to rise again. For the 10x buffer (µ=1.815) it predicts 8.55, but I believe this is outside the range where the equation is valid. Still it is reasonable that there would be a drop in pH upon dilution to 1x. Eaberry (talk) 20:45, 11 January 2024 (UTC)

To adjust pH or not?

" 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)

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)