Chromatography Forum

I have searched the forum for information on peak area responses given a certain concentration of solute/analyte.
The issue at hand is: analyte A has a conc'n of 20 mg/mL, molecular wt = 100; analyte B has a conc of 40 mg/mL, molec wt = 50. Conventional wisdom would assert that an equivalent 1 uL injection of A and B ought to give two peaks with different Tr and similar peak area. This is not what was observed. Peak area of A = 1200; B = 850. Obviously there are more factor in-play here than just vial conc'n and molecular weight.

The issue at hand is chemistry.

Chemistry of the detection methodology.

Chemistry of the portion of the sample which is capable of being eluted and not retained.

weight is linear since the science is physics and the force of gravity.

Response is non-linear and should be, as long as chemistry is involved.

Give particular examples and I can share particular explanations.

best wishes,

Rodney George

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What detector and which molecues? It can make a big difference. My favorite example is carbon disulfide in a FID -- (The "proof" that the FID does not count carbon atoms.)

Don't forget formaldehyde, or carbon dioxide for that matter, right, Don?

Rodney George

I love them. The neat thing about CS2 is that it is such a great sovent for doing GC work - until you take the samples over to the GC/MS. (I know a chromatographer who wondered what was wrong with the GC/MS run - huge solvent tail! The chromatography had looked so good on the FID -- no solvent tail. CS2 did such a great job disolving the crude oil sample. And then I slapped my forehead and felt stupid. )

Re: CS2, no carbon hydrogen bonds, almost no FID response, but it burns really well, to which I was reminded the hard way.

Best regards.

Whose "conventional wisdom" is this ? If you swap the concentrations and have the same heteroatoms in both molecules, and a really specific detector .... maybe. In the real world, not a chance.

Peter

So, based on the heretofore content of this thread, then it is correct to state that molecular weight, number of carbon-carbon bonds, and volatility are not predictors of peak area? If not, then what factors are bona fide predictors?

Who says there are any bona fide predictors?

I don't know of anyone who would, Jumpshooter.

That is why calibration mixes were invented.

Rodney George

1. the baseline appears relatively stable, although the temp ramp of 5C/minute is apparantly causing some shifting but insignificantly.

2. the peak at 30 mins represents about 2/3 concentration as the peak at 14.2 mins, though the area counts between the two are one-half.

Two possibilities:

1) Response factors are different

2) The later eluting peak is decomposed in the inlet or otherwise does not make it to the detector

Can you give the names of the compunds?