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Topic: Determining optimal flow rate in gas chromatography  (Read 248 times)

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Offline confusedstud

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Determining optimal flow rate in gas chromatography
« on: February 08, 2020, 03:56:11 AM »
In an experiment we are supposed to analyse a series of standards to get their retention times for identification purposes. But before that we needed to obtain the optimal linear flow rate by using ethylbenzene as the analyte. We were using nitrogen gas carrier gas. However I don't understand the rationale for this choice since compared to the other components it has the 2nd highest boiling point and one of the lowest polarities.

The other standard samples include o-xylene, toluene, ethanol, n-propanol, n-butanol, n-pentanol, cyclohexane and ethylbenzne itself, which have a spread of boiling points from 78C to 144C and the polarity range is also relatively large. However ethylbenzene does not have the intermediate properties of these analytes so I'm not very sure why it was chosen for this experiment. Does anyone have any insight for this?

Offline Babcock_Hall

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Re: Determining optimal flow rate in gas chromatography
« Reply #1 on: February 08, 2020, 03:17:21 PM »
Do you know the retention order of all of the analyses?  I am not sure whether or not this helps, but it might.

Offline confusedstud

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Re: Determining optimal flow rate in gas chromatography
« Reply #2 on: February 09, 2020, 02:47:46 AM »
Yes, I have identified the following details:
Boiling point   Dielectric constant   Retention times
Toluene   110.6   2 – 2.4   4.714
Ethylbenzene   136   3   6.806
Cyclohexane   80.74   2   1.793
o-xylene   144   2.6   8.875
Ethanol   78.37   24.3   2.632
n-propanol   97   20.1   3.761/3.805
n-butanol   117.7   17.8   5.900
n-pentanol   138   13.9   9.484

So ethylbenzene has one of the latest retention times, but it isn't the biggest so I'm not very sure what makes us choose it for the optimal linear flow rate for all the other compounds. Thanks in advance for the *delete me*

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