Chromatography Forum

Hi anyone,

I am using here GC 7890A Agilent,
I have some questions here regarding this dilution,
Befor liquid injection, I dilute it by CS2 with 1:1 ratio as per , can I use pure sample without diluting it by CS2,
If I use pure sample without dilution, what factors can be involved in this? I mean is there any change in results, percentage recovery?
what is the weight ratio to calibration?
what is the fid dilution factor?

Thanks
Regards
Akbar

Pure sample of what?

Pure sample means, only sample injection without addition of diluent CS2. As you know, we normally inject sample with dilution by CS2.

Regards
Akbar

Davide, normally we crude oil/condensate of testing here in lab, for these kind of sample we use internal standard CS2 as a diluent. So my question is: Can I inject the crude oil/condensate purely without dilution of CS2.

Regards
Akbar

You aren't giving a lot of informations about your analysis issues, but i'll try to help you anyway.
I guess you are doing simulated distillation analysis of crude oil in a GC/FID, probably with a metal column or an high temperature one (like inferno of phenomenex).
You are asking if you can inject crude oil directly instead of a CS2 diluted solution.
I think you are asking this because you find difficult to quantitate the low boiling fraction, the one eluting with CS2?
I'd stick with CS2 solution injection, because the column doesn't have the concentration capacity for that type of injection and you would be overloading the stationary phase with sample.

If your problem is the quantitation of the fraction eluting with CS2, just run a solvent blank before the sample and subtract it from the sample chromatogram, you should be able to quantitate low boiling fraction.

Davide

Mr. Kahn,

I admit I have very limited experience with SimDis analysis. However, I will say this. You are beating the crap out of your column and liner if you are doing a neat or 1:1 dilution of crude oil. I assume you are taking this into account and changing the inlet liner and trimming every few (10-20) injections.

My other question/comment is about how low a carbon number you want to look at. I use a system that gets to C5 with cryo but if you really want to get lower, I would wonder how you are collecting the sample that you think you might keep the C1-C4 intact in the sample.

Might I suggest you contact companies like Separation Systems and discuss with them how they do simulated distillation analysis?

Best regards,

AICMM

You aren't giving a lot of informations about your analysis issues, but i'll try to help you anyway.
I guess you are doing simulated distillation analysis of crude oil in a GC/FID, probably with a metal column or an high temperature one (like inferno of phenomenex).
You are asking if you can inject crude oil directly instead of a CS2 diluted solution.
I think you are asking this because you find difficult to quantitate the low boiling fraction, the one eluting with CS2?
I'd stick with CS2 solution injection, because the column doesn't have the concentration capacity for that type of injection and you would be overloading the stationary phase with sample.

If your problem is the quantitation of the fraction eluting with CS2, just run a solvent blank before the sample and subtract it from the sample chromatogram, you should be able to quantitate low boiling fraction.

Davide

Thanks Davide,
we use CS2 as dilution as per software (chrome perfect) calculation, my question is, can I use sample directly without diluting it. if I do, then what would be the effect on wt % recovery
Regards
Akbar

Mr. Kahn,

I admit I have very limited experience with SimDis analysis. However, I will say this. You are beating the crap out of your column and liner if you are doing a neat or 1:1 dilution of crude oil. I assume you are taking this into account and changing the inlet liner and trimming every few (10-20) injections.

My other question/comment is about how low a carbon number you want to look at. I use a system that gets to C5 with cryo but if you really want to get lower, I would wonder how you are collecting the sample that you think you might keep the C1-C4 intact in the sample.

Might I suggest you contact companies like Separation Systems and discuss with them how they do simulated distillation analysis?

Best regards,

AICMM

AICMM thanks,
this system determine the carbon C1-C35 and C36+

Regards
AKbar

Mr. Khan,

How is the C1 staying in solution?

Best regards,

AICMM

Mr. Khan,

How is the C1 staying in solution?

Best regards,

AICMM

Mr AICMM,

Here in Liquid, It shows very very small peak of C1 & C2 and some time no peak, as it not important in liquid analysis

Regards
Akbar