If by the hump you mean the upward trend in the baseline starting at about 60 min and plateauing out at about 110 min - it is baseline drift, which is normal for a temperature programmed analysis.

Thank you for your answer Mr Apps. 

Your baseline is not good. There are two solutions for drifting baseline (upward). (1) Clean the injector using solvent rinse. If it is not OK, replace the new column. Then, please check the results again.

• Witch column do you use length diameter and films thickness?
• the temperature of  ramp?

Such GC peak may be derived from the chromatographic phase and/or  from less volatile organic components of the coal. The GC column should be heated in high temperature together with the injection from time to time pure solvent. It is good to clean injector and GC column and even to change old for the new GC column.

I doubt that the hump is due to the sample.The problem likely is bleeding of materials off the column at the temperature where the 'hump' starts.  Is it a new column?  What do you see if you just shoot a blank sample and run the same program?  It's bleed if the hump occurs with no sample in the blank.  It's possible that the interesting sharp peaks at longer Rt may show up with a lower max t, but you just have to test it.

If the hump persists, one answer is to use a shorter column, but also with a lower max t.

Coal derived samples are notoriously dirty.  You might want to pretreat the sample with aqueous dilute acid or base.  In addition to a cleaner chromatogram, you might learn something about which peaks are removed by the wash.  If the peaks are due to acid components, you might try derivatising a sample with esterification agents.  I've had good luck with coal derived samples so derivatised.

The problem might be from the inlet system or the column itself. Clean the injector and the column might do the work. Good luck.

It can be due Sevres factors. Dirty injector-clean the injector, Column bleeding- you are losing your stationary phase or what you have accumulated in the column- condition the column, Or there may  be sample is dirty- follow a clean up procedure or if possible collect the head space sample for the analysis. Hope these will help you. If you need further information feel free to contact me.

Mahanama

Dean/Science University of Colombo

I agree with Peter Apps. It is the baseline drift. I suggest you condition the column at the highest temperature you are using for your analysis and repeat the analysis.

Thank you very much for your answers.

Column bleeding, probably due to have reached maximum temperature limit.

If you are using a polar column, such as Carbowax, oxygen is another threat. In this case the column is permanently damaged.

Rather than a constant column conditioning at high temperature, you can try a series of programmed rate from low temperature (the temp. from which you verify the raise of the base line) up max temperature with a isotherm at this temp for 15 – 30 min at a rate 20 -30 °C/min. As a matter of fact, I am not very optimistic, as you base line at higher temp is stable. I it were dirt, the baseline should lowly decrease.

Anyway, before drastic solution you can try:

to clean the injector (liner);

cut 30 – 50 cm of the beginning of the colunm;

turn the column.

Before changing the column you should rinse the column with a stream of solvent from the detector side toward the injector side. This procedure will change your retention time. The choice of the solvents depends on the stationary phase. I suggest to call the column producer for this step, particularly if have limited experience.

 Good luck

AaA

I also agree with Peter Apps.Baseline drift may be also influenced by pyrolysis temperature,you can try to increase pyrolysis temperature depending on the fragments you investigate. 

Agreed with Peter Apps

You should revise application program. 

Peter has pointed out the flaw very rightly.

Kolon fırını sıcaklık programından dolayı bu şekilde bir kromatogram almanız normal, sıcaklık programında muhtemelen 1 ramp var ve sıcaklığın artışı baseline'daki bu yükselme ile aynı sürelere tekabül ediyor. Standart mix solüsyon enjeksiyonunuza da buna benzer çıkacaktır. 

peak'ler güzel ayrılmış ve tanımlanmış. sorun yaşayacağınızı düşünmüyorum.

başarılar ve kolaylıklar dilerim.

It is because of column oven temp. program. Perhaps there is only one ramp at your temperature program and the time of this ramp is matching with the hump on the chromatogram. You will get similar feature when you'll inject your standard mix solution.

Also the peaks are well seperated and well defined, I dont think that you'll face with any problem for further injections.

I wish you success and ease...