assay of a drug product,a syrup, with HPLC

[meudra]

Hi everyone,

I have a huge problem with doing the assay of a dextromethorphan HBr DXM HBr syrup from the US Pharmacopeia. The described procedure is a ionpairchromatography.
I followed exactly the described procedure, but with some small changes, like:
the small changes are:
- column : size : l=0,15m, ID=2,1 mm, stationnary phase = octadecylsilica gel.
- flow : 0,5 ml/min: i choosed this flow, bcs with a smaller colomn, it is not possible the use a higher flow, bcs the pressure problem.
- the mobile phase : in stead of docusate sodium I used Na-docasulfonate,the other components where the same

The problem was that I didnt get a peak after injecting my standard DXM HBr after 25 minutes.
What can be wrong with the method? It's a pharmacopeai method, so it should be correct. Thanks

[Bruce Hamilton]

I followed exactly the described procedure, but with some small changes, like:
...
- the mobile phase : in stead of docusate sodium I used Na-docasulfonate, the other components where the same

Docusate sodium is sodium 1,4-bis(2 ethyl hexyl) sulfosuccinate,
and I doubt your ?suphonate is going to behave the same way.

I don't think I'd call that a small change - unless it was a homologue of the original molecule. I'd recommend obtaining the correct ion-pairing agent would be a good starting point.

Bruce Hamilton

[Consumer Products Guy]

My recommendation (for everyone) is to first perform any assay EXACTLY like a compendial or published procedure, THEN investigate whether any/your modifications make things better, worse, or the same. You need to have something to compare to. How much time ($$$) is lost trying to make something work when purchasing the correct chemicals or columns would've made things more efficient and cost-advantageous overall? Of course, maybe I'm fortunate that my employer agrees with me, and we have an adequate supplies budget.

[meudra]

I used sodiumdodecysulphate as ionpair agent. The reason why I have made some changes is that not everything was available in the lab. I am a student and i dont know what I can do to let this succeed. Can someone help me with [b]tips[/b] to set up another method (i have also the oppurtinity to do Capillary electrophoresis) or give me advices to make the current method that I have now more optimal?Thanks a lot.

[Greg O]

I often assay a syrup containing ephedrine HCl and dextromethorphan HBr, I recieved a method from the Principal which produced no results. After following the USP method for the assay of Dextromethorphan HBr it works if you do not deviate, sodium dicusate is essential. I tried other ion-pairing agents with poor results. The only condition that i changed was the flow rate - 2ml/min which afforded a RT of +/- 3min for the active.

[Bruce Hamilton]

...
Can someone help me with tips to set up another method (i have also the oppurtinity to do Capillary electrophoresis) or give me advices to make the current method that I have now more optimal?Thanks a lot.

I'm not sure what further information you require. Use the correct ion-pairing agent and follow the method as best you can. Using the correct ion-pairing agent will be a great leap forward.

It should not be too difficult to obtain the reagent, sodium 1,4-bis(2 ethyl hexyl) sulfosuccinate. It's commonly known as Aerosol OT
(AOT) or Dioctyl sodium sulfosuccinate (DSS). I would not expect sodium dodecysulphate (SDS) to be equivalent.

Surely it's easier and more efficient to modify a compendial method than to try and develop a whole new technique?.

Bruce Hamilton