Hi,
I'm a student, curently on a research of validating method of simultaneous determination of three active ingredient. I have a trouble with one of them, the dextromethorphan Hbr, it doesn't give time retention even after 25 minutes (curent condition: HPLC varian, 4.6x250mm C-18, mobile phase of methanol:water=30:70 (v/v), 50:50(v/v),UV detection at 270nm)
After several trials, it was undetected. What I wish to ask is, does anybody know a known condition which give some result?
Buffer solution (phosphate buffer, acetate buffer, etc.) that I can use, before I have to use Ion-pairing agents. Thank you very much.

Here is the method for dextromethorphan in the NyQuil mixture along with acataminophen, pseudoephedrine and doxilamine. Ten minutes run with full resolution. Also there is a comparison with regular C18 column.

http://www.allsep.com/makeCmp.php?cmp=Cmp_116