Retention time is the amount of time it takes substance to pass through a column. This can be 5 minutes, 20 minutes etc. When something passes out of the column, and into the detector, (MS is one detector, but there are many different types) it doesn't all come out at once, but over couple of seconds. A little comes out at first, then a whole lot, and then a little at the end, that is why you see a peak that slopes upward and then downward.
What is most important is not the height of the peak, but the area beneath it as this will be directly proportional to the amount of substance that is present. Just for example, if the peak for 1umg of gluteraldehyde has a peak with an area of 50. 2umg would have a peak of 100.
I tried to keep the language simple, and I hope that answers your question. If not, add some comments to the question and I'll edit my answer.
Think about what you measure when you put something on a scale. You're not actually measuring the weight of that thing, you are measuring how much it can compress a spring. If you know how much a 100 lb object can compress that spring and your object compresses it twice as much, you can figure out that your object weighs 200lb based on that.
The same sort of thing is going on here. Your not looking at the amount of substance. If you have a Flame IR detector, you are looking at the amount of absorbence in the IR spectrum, If you have a MS detector, then you are looking at the amount of ionized particles with a certain mass to charge ratio. That part gets technical, but its not that important.
When I use GC in the lab, I always make up a calibration curve based on solutions of known concentration. Basically, I make a solution with a 1 molar concentration, and look at the area of the peak that that produces. If I test an unknown sample, and it produces an area that is twice that, I know the unknown solution is 2 molar.
Hope that helps, If you need more I'll edit my answer again.
· 9 years ago