Hi
I am testing the assay for Hydrocodone.
The problem I am having is the tailing is above 1.00, which is requried. The mobile phase is Phosphate ammonium monobasic and water and MeOH and water. Any suggestion will be helpful.

1.00 seems like an overly strict requirement since it implies that the peak is perfectly symmetrical or fronting. What is your tailing actually running?

Hydrocodone - tails at least a little in every method I've seen for it. Maybe in plasma samples (very low conc.) it would be okay, but for any pharma run, expect some tailing.

try a couple of things (I am assuming this is a USP method):

with a C8 column (which is what I assume you are using) the maximum operating temperature is 60ºC. First, check the temperature of your heater to make sure that it is what the equipment says it is. Try dropping the temperature to 54ºC (within the 10% USP allows). This will prevent the column from losing its endcapping.

increase the flow rate

increase the sampling rate

If you want completely eliminate tailing of compounds like Hydrocodone you may consider to use column technology that was specifically developed for retention of very basic compounds. The idea is to use RP column with embedded positive surface charge rather than negative which is typical for most silica based columns even end-capped. This positive charge eliminates completely any ion-exchange interaction of the basic analytes with acidic silanol residues. Some examples are:

http://allsep.com/makeChr.php?chr=Chr_065

http://allsep.com/makeCmp.php?cmp=Cmp_110

http://allsep.com/makeChr.php?chr=Chr_047

Completely?

USP has postponed the April 1, 2004 revision to Hydrocodone Bitartrate. You can go back to the original method in 27. If you need documentation, go to USP.org, and look at the right of the page for postponed documents