Chromatography Forum

I want to quantify the total petroleum hydrocarbon concentration of the diesel using the GC-FID

And I want to know which is the proper way of the integration.


1. The baseline is linear


2. The baseline follows the peaks


I found some related researches, but both ways had been used...

Which way is the proper way to interpret the concentration of diesel as total petroleum hydrocarbon?

Is there a standard method for this? If yes, doesn't it say how you're supposed to do it?

If not, then to me, the top one is best. The only reason your baseline is rising in that stretch is because you have a mixture of many, closely related materials coming through your column. It doesn't make sense to me to sum them up individually like what's depicted in the second example.

Certainly there is some column bleed. If you include it in your measurement (if you choose the top example as the correct one), does the column bleed skew your final result substantially?

We use the first example. You want to quantify all the hydrocarbons even the unresolved ones. As long as you do standards and samples the same way you should be good. Do you calibrate with a diesel standard or a subset of individual hydrocarbons?

We use the first example. You want to quantify all the hydrocarbons even the unresolved ones. As long as you do standards and samples the same way you should be good. Do you calibrate with a diesel standard or a subset of individual hydrocarbons?

I also use the first example. And, as those on this site have pointed out to me; I now subtract a column compensation run from every run. This takes out the baseline changes due to column bleed and it makes the integration more consistent at the low end of the calibration.

Hi I set this one up for at least a 20 different customers . You are using ChemStation and Agilent developed specific integration events for this application. Please send me an email and I can help you further
BTW number 1 is the correct version. Depending on which protocol you are following you need to do background(=blank) subtraction. As you are also using an Agilent GC you can do column bleed compensation on the GC prior to inject anything, then the bleed is already compensated at the GC itself.

You do not make it clear on what you are trying to achieve. The top chromatogram is to me Simulated Distillation, and this would be the correct integration. The second integration shown is for DHA, Detailed Hydrocarbon Analysis.

From your run time, I guess that you are trying to do Simulated Distillation, and you will need special software. You should also check out the ASTM methods, as there are several methods depending on the boiling range of your sample.

A DHA analysis would need a much longer column and runtime.

Gasman

You do not make it clear on what you are trying to achieve. The top chromatogram is to me Simulated Distillation, and this would be the correct integration. The second integration shown is for DHA, Detailed Hydrocarbon Analysis.

From your run time, I guess that you are trying to do Simulated Distillation, and you will need special software. You should also check out the ASTM methods, as there are several methods depending on the boiling range of your sample.

A DHA analysis would need a much longer column and runtime.

Gasman

Hello GasMan, and thank you so much for your comments.
Actually, I want to quantify both of them, TPH & each alkane (octane to docosane) concentration
According to your comments, I think I need to increase the runtime by changing the oven programme to measure the second one... (i.e. ramping rate)

However, since I use FID (Flame Ionization Detector) and HP-5 column, I'm worried about if it is possible without changing the instruments or column type.

So my additional question is, is it possible to do DHA with FID and HP-5 column?

Here are some information of the apparatuses I'm using now.

Instruments: 6980N Network GC system, Agilent Technologies, USA
Column: HP-5 capillary column (30 m × 0.320 mm × 0.25 μm)
Carrier gas: N2 (nitrogen gas)

Again, Thank you so much for your advice and comments

Thank you for all your comments!

I learned so much and got some insight into what I'm doing now...

I will find out and try what you have suggested.

Thank you again!