Chromatography Forum

Is it common to see foaming in mobile phase when using sodium dodecyl sulfate in the preparation?

Especially if that mobile phase is still 100% aqueous !!! Sodium dodecyl sulfate is a great anionic surfactant !

Especially if that mobile phase is still 100% aqueous !!! Sodium dodecyl sulfate is a great anionic surfactant !

Would you suggest the SDS solution needs to settle for long before adjusting the pH?

Would you suggest the SDS solution needs to settle for long before adjusting the pH?

There is a method for tranexamic acid related substances in Eur. Ph. with the following MP preparation:

Dissolve 11.0 g of anhydrous sodium dihydrogen phosphate R in 500 mL of water R and add 5 mL of triethylamine R and 1.4 g of sodium laurilsulfate R. Adjust to pH 2.5 with dilute phosphoric acid R and dilute to 600 mL with water R. Add 400 mL of methanol R and mix.

SDS makes the buffer solution foaming, but this is not critical. No precautions are needed to adjust the pH of this solution.

I have visions of someone trying this on a ELSD or CAD. Of course it would kill the detector because it's non-volatile, but just imagine what the lab would look like after half an hour or so...

And once the methanol is added, suds should be a non-issue.

I might determine accurately how much phosphoric acid I needed to add, then after that first time add the phosphoric acid by weight or volume for subsequent batches.

With our mixed-mode columns you have ion-pairing reagent attached to the surface. Nothing is going to ever foam .
Contact me if you would like to chat about any of your applications which uses ion-pairing reagents and how to convert them to methods fully compatible with MS, ELSD, CAD or UV.