I am reading a TLC message for a quaternatary amine bromide that includes sodium or potassium iodide in the mobile phase. What role does the iodide salt play? I have seen chloride salts before but not iodides? Could the iodide be replacing the bromide anion in the quat to make it more mobile or chromatographable? If the iodide works, would the chloride salt be as effective? Is the purpose of the inorganic salts to control the polarity of the mobile phase? ???????

Stan Alekman

Did you read my post above in the "benzethonium chloride" question? Here it is again:

Although not the same, I have analyzed pancuronium bromide (another quarternary amine) in biological samples at levels around 0.10 mg/100 mL using 5 mL sample--but it was by TLC. You can probably adapt this to HPLC pretty easily:
Silica TLC plate
Developed in 90% ACN/10% 1M Magnesium perchlorate
(the perchlorate is for ion pairing and I don't think that you specifically need magnesium perchlorate, it was just what I had laying around.)

I used Iodoplatinate to develop the spots, as pancuronium bromide has no chromophores. If your compound has chromophores, you can go with UV detection; if not, then MS would probably be good.

This method was adapted from "Analysis of Steroids. XLI. Ion pair HPLC separation of quarternary ammonium steroids on silica" j. chromatogr. 1991 jul 26; 550 (1-2): 639-44
You don't have a steroid there, but this might be somewhere to start method development from.

The perchlorate works the same as the iodide in KI--to ion pair and move the quarternary amine up the TLC plate. In my research for the method, I didn't find anything that said that chloride salts would work. That's not to say that it WON'T work, I just didn't try it.

Hope this helps some!
Lisa