I want to try separating lineær alkylbenzen sulfonats on C18 by ion pair chromatography. I will try with tetrabutylamm. as counter ion and gradient acetonitril/Water. Do you have some experience with sush an analyse please let mee know.

Hi Henrik!

Why do you want to use an ion pair agent to separate LAS on a C18 column?? Indeed there is no need to use it. If it is not necessary to resolve phenyl isomers, it is advantegeous to separate on a C8 column instead of C18.

What kind of detector do you use? UV or MS?

peter

You can also try to separate the sulfonat on NS1 5µ column with a suppressor from DIONEX, use an ion pairing with NH4OH if you have long Alkylchain and tetrabutylammonium hydroxyde for short alkylchain and use the conductivity detector.

LAS is best analyzed using a C-18 column, water-ACN eluent containing at least 10mM electrolyte. Resolution and efficiency on a silica based C18 column is significantly better than that observed with a porous polymer column. Raising ionic strength will help increase efficiency. True ion pair reagents are not needed, indeed they only increase the amount of solvent needed while decreasing resolution. As you are probably aware this is actually a mixture of 30-50 related compounds so you shouldn't be expecting to see a single peak or even to see all peaks resolved. Generally, components elute in groups (e.g. all LAS components with a C10 hydrophobe, then all LAS components with a with C12 hydrophobe, etc., with partial resolution of the different branch structures containing the same carbon number). Detection can be either via UV or conductivity (in the latter case a suppressible electrolyte such as ammonium borate-boric acid should be used). Joachim Weiss' book: Ion Chromatography (second edition) has more details.