Please look at the following below links which may help you in your analysis:

https://tools.thermofisher.com/content/sfs/posters/87422-PO-HPLC-Surfactant-Analysis-08July10-LPN2525-1.pdf

Thanks

Dear Adam,

Determining the 'free' surfactant concentration in a surfactant solution above the cmc is not straightforward. Most analytical methods require, or cause, some kind of dilution which would possibly bring the sample below its cmc. The free surfactant concentration is however equal to the observed cmc. Determining the cmc can be done by a number of methods. I have good experience with conductometric titration. One simply dips an accurate conductance cell in a weighted amount of milli-q or deionized water and stepwise adds the surfactant to be studied. Before the cmc the slope of the increase of conductance of the solution is linear with concentration, at the cmc a distinct break occurs (as micelles conduct less than free surfactant ions). Establishing two line sections (one before and one after the cmc) and determining the intercept of them gives you the cmc i.e. the free surfactant concentration.

I would do it like this:

1. Prepare the surfactant mixture at 10 times cmc. Surfactant concentrations should be known accurately.

2. Weigh in 50.00 grams of deionized water into a titration cup, add a stirrer bar and place on magnetic stirrer.

3. Dip in the conductance cell and register the conductance value.

4. Stepwise add 0.5 ml of surfactant mixture (using a calibrated pipette), register conductance when the value is stable.

5. Repeat step 4 for 20 times (which means adding in total 10 ml to give a final solution volume which is 60 ml, at this point you are at 1.666 times the cmc).

6. Plot the data in a scatter plot graph (Conductance versus surfactant concentration; surfactant concentration at each point can be calculated, don't forget to perform volume correction for the added surfactant solution).

7. Establish the two line sections and determine the cmc from the intercept of the lines.

This is simple, requires no expensive equipment and is fun to do.

If your data doesn't generate tow nice line sections, please consult: Article A Comparative Study of the Determination of the Critical Mic...

Hope this helps, kind regards, Leo

Kedves Leo,

Köszönöm a részletes választ és az instrukciókat. Lehet hogy nem volt világosan bemutatva a probléma felvetésem. Olyan technikát keresek, amely képes különbséget tenni a micellába integrált és a szabad tenzid között.

Kedves Ádám! Valóban ionos és nemionos felületaktív anyagok keverékeivel dolgozik. Ezt a tényt figyelmen kívül hagytam, a kevert micellák összetétele eltérő lehet. Talán a H-NMR segíthet az ott tartózkodó embereknek. Bár valójában nem egyszerű tantermi kísérlet .... Üdvözlettel, Leo