crystallisation of PBS (10X) - (Feb/05/2014 )

Hello everyone,

I prepared a fresh PBS stock solution (10X) and after few days in the fridge (4°C) I observe some crystallisation on the bottom... which disappears when i heat up the whole solution again...

Is that normal? For information, i mixed the following (in 1L of milliQ water):

- 80 g NaCl

- 2g KCl

- 18.05 g (Na2,HPO4)(2H2O)

-2.4 g KH2PO4

and then i adjusted the pH at 7.4 with HCl.

can you describe the crystals (shape, color, etc)? that may give a clue as to their origin.

It is very nice actually :)

It is sharp, more or less leaf-shaped, several arborescent monolayers ... Not sure that will help you^^

Do you always use that much disodium phosphate? We only use ~14g, it is possible that you oversaturated the solution and it is precipitating out. 

sodium phosphate (and that includes the potassium phosphate in your solution due to ion exchange) will crystallize at refrigerator temperatures (~4C).

Stock solutions at 10X or 20X PBS usually precipitate in the fridge. I leave mine out at room temp though. 

Autoclave and leave at room temp, that's what I do. Such saturated solutions alway precipitate in the fridge.

I've seen 10x PBS precipitate in the fridge as well.  I've also noticed that some buffers will precipitate when stored in a glass bottle but not in a plastic and that in both cases they re-disolve when warmed.

Ok thank you all of you for your responses, this comfort me, as suggested i think that the best remains to autoclave and leave at RT...

I had prepared a 10X PBS autoclaved and kept it in room temperature for many days (a little over a month). It was okay for a long time but recently some thread like (i mean white cloudy strands) floating in the solution. I had also filtered the solution prior to autoclaving and storage. What  could be the cause?