Heart-cut effect has us stumped!

[Chemy]

I am working on the timing of a heart cut to cut out a matrix gas using a 100ppm standard of the matrix gas in helium. I've run into an interesting phenomenon that has stumped me and others with whom I work.

I have run a sample throught the column with the valve switched on at the beginning of the run and left on throughout the run and recorded the peak area. Then, when I run a sample switching the valve on at the beginning and then off a few seconds later and then back on a minute later, the peak comes off the column about 5 minutes earlier (expected) and the peak area is about 3 times greater than when I leave the valve on for the duration of the run.

The peak area is what has us stumped. Does anyone have any possible explaination as to why we are seeing a 3-fold increase in peak area when we switch the valve off and back on during the run?

[chromatographer1]

Depending upon the gases involved and the hardware setup and the kind of valves you have and the exact plumbing involved there can be several reasons.
Since I dont have an extra hour to type all the possible situations the short answer is you are dual injecting a larger sample onto your column or you are bypassing a column where the peak has losses normally in area or is broadened out and is integrated differently to give you a smaller area.

And sometimes you are doing things you don't realize you are doing. Knowledge and experience can be worth a lot in solving issues like this.

I would suggest you get an experienced multidimensional chromatographer to assist you. But (sorry for the plug) companies don't seem to want to pay for knowledge and experience, they expect to solve their problems for free rather than contracting a professional consultant or process analyzer company.

There are several good companies and consultants who post on this forum. AICMM is one, and there are others.

best wishes,

Rodney George
CONSULTANT

[tigerk2001]

I totally agree with chromatographer 1.

It looks like you're dual injection what make your sample volume(analyte volume) bigger.
Normally, an injection is turning on for sometime around 30 seconds and turn off the rest of the cycle.
I already have seen some strange phenomenon with cross port leaking valve. Specially with VICI.
Let me know if you want more support.

Chromatographer was also right about the fact that no company is ready to pay for such kind of good experience support!!

anyway! for my part I like to help when I can