GLC Question

[slothpomba]

Pg 75
(18) The organic compounds dimethyl ether (CH₃OCH₃) and ethanol (CH₃CH₂OH) have the same molecular formula, C₂H₆O and the same molar mass, however they have different structural formulas.

A sample containing both ethanol and dimethyl ether is analyzed by GLC using a flame ionisation detector.

(A) Will the two compounds produce peaks with the same retention time? Explain your answer


I would say, yes, they do have the same retention time, because they essentially contain the same thing. This seemed like a resonable answer to me.. but since theres a part (B) i figured the answer to this question must be no. Thoughts?

(b) If the sample has the same concentration of both chemicals, will the peaks produced have the same area, Explain

I would also say yes, thoughts?

[superflya]

1a) look into the bonds, polar, non-polar etc

[fady_22]

a) No, they will not have the same retention time. Although they have the same molecular formula, they have different structural formulae. This affects the bonding between each the compounds (i.e. dimethyl ether is non-polar, dispersion forces exist and ethanol, polar so hydrogen bonds). The difference in bonding causes each of the compounds to adsorb/desorb at different rates, producing different retention times.

[Martoman]

Pg 75
(18) The organic compounds dimethyl ether (CH₃OCH₃) and ethanol (CH₃CH₂OH) have the same molecular formula, C₂H₆O and the same molar mass, however they have different structural formulas.

A sample containing both ethanol and dimethyl ether is analyzed by GLC using a flame ionisation detector.

(A) Will the two compounds produce peaks with the same retention time? Explain your answer


I would say, yes, they do have the same retention time, because they essentially contain the same thing. This seemed like a resonable answer to me.. but since theres a part (B) i figured the answer to this question must be no. Thoughts?

(b) If the sample has the same concentration of both chemicals, will the peaks produced have the same area, Explain

I would also say yes, thoughts?

I would have to disagree with the second, if only because of intuition. Even though they are the same thing, they have different structures. This means they will interface with the detectors differently.

The peak area depends on the sensitivity to a detector, if you are using the flame ionization one as is standard, then its sensitivity to that. If you have different interactions with the detector, it means different peak areas.

[fady_22]

Pg 75
(18) The organic compounds dimethyl ether (CH₃OCH₃) and ethanol (CH₃CH₂OH) have the same molecular formula, C₂H₆O and the same molar mass, however they have different structural formulas.

A sample containing both ethanol and dimethyl ether is analyzed by GLC using a flame ionisation detector.

(A) Will the two compounds produce peaks with the same retention time? Explain your answer


I would say, yes, they do have the same retention time, because they essentially contain the same thing. This seemed like a resonable answer to me.. but since theres a part (B) i figured the answer to this question must be no. Thoughts?

(b) If the sample has the same concentration of both chemicals, will the peaks produced have the same area, Explain

I would also say yes, thoughts?

I would have to disagree with the second, if only because of intuition. Even though they are the same thing, they have different structures. This means they will interface with the detectors differently.

The peak area depends on the sensitivity to a detector, if you are using the flame ionization one as is standard, then its sensitivity to that. If you have different interactions with the detector, it means different peak areas.

Yep... I'm wrong on the second question.