One usually makes an SDS solution in distilled water, which actually has a pH of 5.5 - hardly alkaline. The precipitation is due to the formation of the potassium salt of SDS, which is insoluble. This phenomenon forms the basis for the removal of bacterial/protein debris in alkaline lysis preparation of DNA; or stopping some enzyme reactions using potassium based buffer system by addition of SDS to unfold and then precipitate the enzyme.

the precipitation is due to ph. SDS disloves only in alkaline ph So if you add NaOH you will get a clear solution. when you get clear solution the ph is close to or is 8.

Thanks a lot.

The buffer was already at about pH = 8, but I'll add a little NaOH!

One usually makes an SDS solution in distilled water, which actually has a pH of 5.5 - hardly alkaline. The precipitation is due to the formation of the potassium salt of SDS, which is insoluble. This phenomenon forms the basis for the removal of bacterial/protein debris in alkaline lysis preparation of DNA; or stopping some enzyme reactions using potassium based buffer system by addition of SDS to unfold and then precipitate the enzyme.

...if you use a sodium-based buffer, you can increase the tolerance of the solution to SDS addition quite considerably.

Indeed, the solubility of potassium SDS is much lower than its sodium variant. Just use a sodium-based phosphate buffer and your problem is "solved" ;) At 4°C, some precipitation may occur, but it disappears when warming to room temperature. Good luck!

when you add SDS to the buffer the ph of the buffer changes dramatically so you have to again add NaOH to get it to right ph. you can see the effect of ph by adding HCL and then NaOH. the more you add HCL the more thick solution it becomes and arlast it becomes like a paste. but if you keep on adding NaOH to the same thick paste like solution it will turn clear solution. so its all about the right ph to dislove the SDS.

hope your problem is sloved.

do let me know.

have a great day.

dissolving in a sodium phosphate buffer with specific pH (e.g. 6.8) does not need or only minimal pH adjustment. This is easier to my opinion. Using a potassium phosphate buffer with the same pH yields a precipitation. If Alice needs a solution at a specific pH, it is not always evident to adjust pH. So, I should prefer my way ;)

Potassium Dodecylsulphate is insoluble in buffer condition. Addition of potassium ions will remove dodecylsulphate by the precipitation of potassium dodecylsulphate.

Indeed, the whole point of this is presumably for a buffer at a standard pH range, (6.8 - 8.5) I have never felt limited to a particular pH just because I'm using SDS, this is because using a sodium salt *solves the problem*. As pH is likely to have a greater effect on the observed experiment than the monovalent cation, I'd err on the side of buffer choice than pH.

Thank you for all your comments.

Jamie's and Frank's suggestions seem to make a lot of sense.

I tried Tris buffer instead of potassium phosphate which worked fine!

If you use K ions, precipitation can be avoided if you use Lithium Lauryl Sulfate

It neither matters in which order the chemicals are added, nor does it matter which lauryl sulfate salt (sodium or lithium) is added: If there are potassium ions in the solution, you will always get a unsoluble precipitate. The only way to get around this is to use another buffer that contains no potassium or use another detergent.

Not true. Most likely Lithium binds much tighter preventing potassium from binding and therefore preciptating dodecyl sulfate. You can therefore get away using much more potassium in your sample when you use Lilauryl sulfate versus sodium lauryl sulfate.

Lower temperatures can also precipitate SDS buffers, although that is unlikely the case here.

I had this problem with 150mM KCl in my lysis buffer, but one sample I accidentally diluted 2 fold with the same buffer except it had 150mM NaCl. I took 20uL of each lysate and added 20uL of 4x sample buffer. After boiling, the 150mM KCl-containing samples had a white precipitate (~ 8uL pellet). I still loaded the samples after spinning down the small precipitate, figuring that the samples had enough salt and sds to run properly and they seem to be running normally. If this is a recurring problem, use NaCl instead at 150mM, never had issues at that conc.

whats the purpose of adding HCl to SDS solution??