Welcome

I would also like to welcome everyone to the environmental analysis section of Scientist Solutions.

In performing analytical chemistry on environmental samples, we are often faced with issues which range from sample prep to the instrument. The problems are often confounded when the issue may manifest in one part of the process, but the solution may be in another.

With hope, through this forum, we should be able to assist each others with the problems we face in this area of research.

Sincerely,

Greg Pronger

I am new to organic chemistry analysis in the environmental field.  I am having low IS response.  I believe there could possibly be a leak problem.  I was wondering if someone could give me some other options to try.

First, I will assume that the mass-spec is behaving "normally"; obviously if the mass-spec is not operating correctly, all bets are off on your quantitation. That being said, most chromatography problems are either in the inlet or that you have active sites at the head of the column, both are typically addressed by routine column maintenance.

Our instrument chemists, prior to each day's samples, are replacing the inlet liner and base-plate. They will also remove about 4 - 6 inches from the head of the column. Once doen they reassemble, allow the inlet to become oxygen free, and then heat it up. We will typically inject a solvent blank once or twice to equilibrate the system.

To solve a leak, I would simply go and verify I haven't left somethig loose, or that when I installed the column, it did not slip down and that I do not have the correct length of column above the capillary ferrule.

To give you much more help, we'll need more info, such as instrument, type of injection, (split - splitless, etc), and what analysis.

Greg

I am currently using an HP 6890 GC/MS system.  I cleaned the ion source and am fairly positive that I have a leak, but have trouble determining where it could be.  I have tighten everything that I could think of.  Do you have any suggestions of how I could narrow down where the leak is?  Thanks for your pervious suggestions.

First, is there are in your background? If so, we use the compressed cans of gas for spray dusting circuit boards. You simply monitor the primary ions of the stuff (one of the freons, the can will say which one) and spray the fitting and seals on the mass-spec. When you suddenly see the ions, then you've found your leak.

If you don't have air in the background but are experiencing a loss in sensitivity, ramp each of your lens and make certain that they all look normal. If any don't ramp smoothly, but insteand are "noisy" then there's a problem with the reassembly of the source.

If what you're asking about isn't a mass-spec leak, but a GC leak, we use the leak detectors which respond to helium. They cost some money but I really like the leak detectors. I believe Restek sells one as well as Gow-Mac. They can "sniff" helium which is a lot better than squirting the liquid leak check stuff, which I then always worried about somehow getting inside.

Greg