Chromatography Forum

Hi,
I was wondering if there is a general method to determine carry-over.
(On GC-MS) I usually do 3 consecutive injections of a high concentration sample followed by a blank, then another 3 high concentration injections followed by three injections of a low concentration. It's been called redundant by some, smart by others, but it's a system that's worked well enough for me so far (I think). But I can't help but wonder if there is an "official" way.
Thanks!

Your system errs on the side of caution I would say. A high level standard or a sample with plenty of analyte followed by a system blank is the way that I do it. If I find carryover I then run blanks of various steps to try to isolate where the carryover is coming from.

Peter

Thanks Peter,
Yes, I assumed my way might be a bit overkill.
Thanks for your input!

Hello,

I am having a problem with carryover in my system. I posted about this a few days ago in the LC Forum under the name "Column Contamination". It turns out that it is not my column, but I am seeing a carryover peak near the end of my run which is interfering with the recoveries of my lower concentration calibrators.
Peter, in your reply you say you run blanks of various steps to isolate where the carryover is coming from. Could you elaborate on this?

Thank you.

Suppose for example that you have a method that involved extraction, solid phase cleanup, evaporation, injection, separation. To isolate where carryover or contamination is coming from you either run one step at a time (of course you have to do an injection to do a separation) or you eliminate one step at a time (and, yes, you cannot eliminate the injection or separation). Whatever makes the problem go away is the source of the problem. You might have multiple sources of contamination or carryover - for e.g. in GC a filthy inlet often goes with a contaminated column.

Peter