Making a Phosphate Buffered Saline - (Oct/19/2012 )
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.
I know this is probably pretty basic, but I was hoping someone could help me out with this.
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.com/quickcalcs/molarityform.cfm
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)
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 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
Great thanks. I'd still be curious if my calculations were right if anyone wants to comment on them.