method development

[olivia]

Hi, say I was given a method to develop for the analysis of acetaminophen and its impurities (suppose we don't know what these are). Starting with the bulk drug, do I perform forced degradation studies on the acetaminophen. Acid/base/peroxide/temperature/light. I also prepare a fresh sample of acetaminophen prior to running the hplc.

Acetaminophen has an amide group which is very stable and not overly susceptible to interaction with acids or bases without heat. However, with heat amides can hydrolyse to the carboxylic acid via acid or base. Therefore, is para aminophenol a potential product or not?
I think the phenolic group can oxidise to a ketone, but I thought this to be more likely for diphenolic compounds.

Finally, from the web the pKa of acetaminophen is about 9.4. Therefore its probably best to run this analyte in low pH mobile phase. However, at this pH THE perhaps a phosphate buffer of pH3 using a C18 column based on modern silica, eg hypersil gold.
Wavelength of detection about 254nm.
Can someone please comment if my thinking is on the right track
Many thanks
Liv

[Bryan Evans]

Below are analgesics separated on Unison UK-C18:

http://www.silvertonesciences.com/files/TI165E.pdf

p-aminophenol test is in the USP monograph

[Dan]

Acetaminophen is fairly stable, either as the drug substance itself or within a drug product. You may not get it to yield any degradation products in a forced degradation study, but you may get something. It's not heat or light sensitive.

About the only degradant to worry over is the p-aminophenol. As Bryan noted, you can look up the USP monograph for a test for it.

You can also look in the EP/BP for monographs there. Just remember to look under "paracetamol" which is the name used in Europe and elsewhere for acetaminophen.

Regards,
Dan