[baseball07]

Hello I am trying to make a PBS buffer with 1% SDS (sodium dodecyl sulfate).  My question is, does the 1% refer to the other granular chemicals in the solution?  That is, if I have 7.32g of NaH2PO4, 48.0244g Na2HPO4, 36.008 g NaCl, and .4g of NaN3, the total grams of substance in my solution would be 91.75 g.  So I would need to add .9 g of SDS?  Is this correct? 

[JGK]

% units can be in the following terms

% w/v where 1% is 1 gram of solid dissolved in 100 mL solution.

or

% w/w where 1% is 1 gram of solid mixed in 100 g of the matrix.


I suspect that, as you are dealing with a buffer solution, the % will be w/v (but confirm). However if the density of the buffer (without SDS) is 1.00 g/mL it does not matter as both will be identical.

[baseball07]

Ok. So if I am making a 500 mL buffer solution, I need to add 5 g of SDS ( assuming 1g per 500 mL)  Correct?

[JGK]

Ok. So if I am making a 500 mL buffer solution, I need to add 5 g of SDS ( assuming 1g per 500 100 mL)  Correct?

Yes.

[baseball07]

Hey everyone.  I mixed my PBS with 1% SDS and the SDS did not dissolve in the PBS.  Should I have added the SDS as a step in my PBS preparation.  Where can I add the SDS so I get it to completely dissolve?

[Arkcon]

SDS is pretty soluble in water, and a 1% solution should be no problem.  Of course, it foams a lot, so you wouldn't want to mix it too vigorously, just very thoroughly.  That's not a joke.  That is to say, spend more time mixing it gently, instaed of going for a rapid shaking.  The dry SDS powder can also float on it's foam, as can your other solids.  The best way, to mix just about anything, just about any time*, is to dissolve all salts in a portion of the final amount of water, say half, or three quarters of the final volume, dissolve well, add surfactant, mix thoroughly to dissolve, let foam subside, then fill to final volume.

*Disclaimer: for some very insoluble salts, this is hard to do.  Also, other detergents, of the sort I'd use in a plating bath, can foam so badly even this won't work.  So YMMV.