I have been runnning the same method of analysis for Retinol Palmitate for about 2 years now and have begun to notice various problems in the run. I have carryover and matrix interference. I use a syringe with a .45um filter for cleanup of the sample before injection. The process involves blowdown with a N-Evap Nitrogen evaporator. The column has been replaced and the mobil phase checked.(6%H20 25% MeOH and 69% ACN) Any ideas anybody as to why I have such a messy chromatogram suddenly!

Carryover problems that appear where you never had them before are lilkly due to a hardware problem of some type. I have seen things like malfunctioning needle wash pumps (or empty needle wash bottles) cause problems like this. As for your matrix interference problem, it could too be related to some autosampler hardware faults. N-Evaps can also become contaminated with time causing crossover between blanks and samples, this looks just like carryover when you run the blanks.

The fact that your method worked well for 2 years and suddenly does not should tell you where to look to solve this problem. Look for things that might have changed since time time it last worked well.

Good Luck

A.A.

Any part of your N-evap system may be causing problems--including the gas you are running through it.

I had a problem once with a regulator. I replaced the broken one (SS diaphram) with a borrowed one (rubber diaphram), and immediately started seeing all kinds of junk in my samples that weren't there before.

Just today we determined that a contaminated tank of argon/methane was increasing our electron capture detector baselines from 200-500 to 30,000, putting us out of business.

Something is indeed different in your analysis, and it may not be easy to find. Work systematically, carefully, one step at a time, documenting what you're changing. It may even be a combination of things all going haywire at the same time--the straw vs. camel's back problem.

Good Luck!!!