Gaschromatography question

[augurys]

Hello guys,

For Chemistry we have performed a gaschromatography experiment with a nano2-gaschromatograph with nonpolar/apolar column. The stationary phase is probably a GLC but we aren't sure since we weren't informed on it and I don't know whether it'll be relevant to the question I'm gonna ask. For the experiment, we had to identify the substances in the gas of liquid lighters, and capture their retention time.

Now the question we were asked: What can you change from the experiment to make the peaks (the retentiontime) of the different substances further away from each other in the chromatogram?

I am still in high school so I probably know nothing about university-terms.

I would be very grateful is someone would know the answer.

Some desperate suggestion we've come up with are:

- a thinner column

- a longer column

- increase flow rate (???)

[studiot]

The term you are looking for is selectivity (as opposed to sensitivity which is the minimum detectable amount).

 

Here is a good start.

 

http://www.restek.com/Technical-Resources/Technical-Library/Editorial/general_GNAR1743-UNV

 

Is this homework?

[augurys]

The term you are looking for is selectivity (as opposed to sensitivity which is the minimum detectable amount).

 

Here is a good start.

 

http://www.restek.com/Technical-Resources/Technical-Library/Editorial/general_GNAR1743-UNV

 

Is this homework?

Thank you!

 

It's for a report, but there are specific questions we have to answer too. I guess you could call it homework?

[studiot]

Hello augurys and welcome.

 

We call any form of submitted work homework.

 

You should read this.

 

http://www.scienceforums.net/topic/75772-read-this-before-posting-in-homework-help/

 

But don't be afreared, there are several expert Chemists here, who love to help those who help themselves as well.

[CharonY]

I have moved it to homework for now. Now as you may have noticed your question is about how to separate the compounds better. Note that the retention time does not need to change (though it can) as a narrower peak would also give you better resolution (i.e. less overlap of the peaks).

So basically you want to influence retention time and/or peak shape and there are many ways to address this. Your two first answers address the column. Do you know the relationship of length and diameter with chromatographic resolution? I am not sure how much is taught on the HS level, and you may not need to know it, but it certainly will help to understand the concepts if you look up the concept of theoretical plates and the resolution equations.

 

Same thing regarding flow rate. What do you expect to happen if you increase/decrease it.

What other parameters can you think of?

Also think in terms of peak shape. Are they nicely symmetric?

[BabcockHall]

One way to think about gas chromatography is that it separates molecules on the basis of their relative tendencies to be in the gas phase versus a particular liquid phase. What can the experimenter do to affect this partitioning?