I need to make 500mL of the following Phosphate Buffered Saline (normally I buy it pre-made, but we ran out of it),

0.1M Sodium Phosphate, 0.15M NaCl.

pH ~7.2

I know this is probably pretty basic, but I was hoping someone could help me out with this.

Submit your paper to J Biol Methods today!

# Making a Phosphate Buffered Saline

Started by Gradstudent78, Oct 19 2012 12:26 AM

4 replies to this topic

### #2

Posted 19 October 2012 - 01:05 AM

Calculate the amounts... then adjust pH.

I recommend you prepare a 10X solution so you have to prepare it only once.

If you have problems with calculations you can use this for help: http://www.graphpad....olarityform.cfm

I recommend you prepare a 10X solution so you have to prepare it only once.

If you have problems with calculations you can use this for help: http://www.graphpad....olarityform.cfm

### #3

Posted 21 October 2012 - 12:01 AM

Ok this is what I've come up with for the amounts (making 1 Liter instead of 500 mL, a 10x solution would probably just be a waste as I only have to use this every couple of months):

I used Henderson-Hasselbalch equation for the sodium phosphate concentrations, using a pKa value of 6.865 (I'm a little confused on this as some places say it's 6.86 and some say it's 7.21)

7.2 = 6.865 + log (Disodium phosphate Dodecahydrate/Monosodium phosphate monohydrate)

Results:

24.490 grams of Disodium phosphate Dodecahydrate

4.363 grams of Monosodium phosphate monohydrate

For the NaCl I calculated:

8.766 grams of NaCl

I used Henderson-Hasselbalch equation for the sodium phosphate concentrations, using a pKa value of 6.865 (I'm a little confused on this as some places say it's 6.86 and some say it's 7.21)

7.2 = 6.865 + log (Disodium phosphate Dodecahydrate/Monosodium phosphate monohydrate)

Results:

24.490 grams of Disodium phosphate Dodecahydrate

4.363 grams of Monosodium phosphate monohydrate

For the NaCl I calculated:

8.766 grams of NaCl

**Edited by Gradstudent78, 21 October 2012 - 04:18 AM.**

### #4

Posted 21 October 2012 - 04:25 PM

I don't know why you are making so much calculations. There are tables to make phosphate buffers almost directly without fiddling with the HH equation

http://www.sciencega...endix/phosb.htm

http://www.sciencega...endix/phosb.htm

**Edited by El Crazy Xabi, 21 October 2012 - 04:29 PM.**

### #5

Posted 23 October 2012 - 06:34 PM

Great thanks. I'd still be curious if my calculations were right if anyone wants to comment on them.