Chromatography Forum

I have a quaternary ammonium salt with a UV at 205nm. It is unretained on RP without ion-pairing. The problem is that with all the ion-pairs that I know they have strong UV adsoprtion.


ANy ideas,

Depends on the concentration that you need to detect. There is a technique around with UV-absorbing ion-pair reagents, where you look for the concentration of the ion-pair against the ion-pair background to detect the analyte. You could use that trick, but I doubt that the sensitivity is very high.

Alternatively, you could try HILIC with a silica column and an acetonitrile-phosphate buffer mobile phase.

Hi Malcolm,

Here are few applications for retention/separation of quaternary compounds on Primesep columns. No IP reagent required. Compounds are retained based on reverse phase and cation exchange (anion exclusion) mechanisms:

http://www.sielc.com/compound_080.html

Contact me directly if you need more information or would like us to develop method for you (free of charge).

Regards,

Vlad

You can try 10mM HClO4 as an ion pairing agent; it ion-pairs about as well as TFA, and has much better UV properties. The alkane sulfonic acids have good UV properties and are stronger ion-pairing agents. You can also look into evaporative light scattering or suppressed conductivity detection. I have done quaternary surfactants like benzalkonium chloride on an Acclaim Surfactant column with conductivity detection, and it gets better detection limits than ELSD and sometimes better than UV.

mross,
the common used IP are alkane sulfonic acid and tetraalkylammonium. I do not have an impression of either one having strong UV.
Could you let me know what kinds of IP you tried?Thanks

Hi,

I realise it's a while since this was posted, however.

We have some experience of quartenary ammonium salt determinations by IC.

Iodine salt of Bis-Dibutyl Ethyl Ammonium Hexane is analysed on Dionex NS1 columns.
MSA eluant with methanol solvent.

Drop me an email if you want any information

mross,
Another possibility is using HILIC. One typical example can be found in the following web address: http://www.sequant.com/sn/ufiles/SeQuan ... 00-14A.pdf