Anon asked in Science & MathematicsChemistry · 9 years ago

I have several chromatograms. I have a basic idea of how a GC/MS works, but I don't understand exactly what is the detector response and retention time. What does it represent? In simplest terms please! I'm only sixteen. I'm not learning this in class, I need to know for my science fair project.10 points best answer. Thanks in advance:)

Update:

A.C. Thank you! It helps, but I still don't understand what detector response is, could you please explain to me what it is representing on the chromatogram? Is it the amount of that substance?

Relevance
• Anonymous
9 years ago

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.

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.

• ?
Lv 4
9 years ago

Detector response is just the detector "sensing" chemicals of interest. It is represented by the line on your chromatogram going up "in response" to sensing chemicals. You can develop a calibration curve with known amounts of your chemical by integrating the area under the peaks in your chromatogram. Then you run your unknown sample, integrate the area under the peak, and compare it to your calibration curve to determine how much is in the unknown sample.

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