Check the liner maybe replace it

Secondly cur 5-10cm of your column from the injector side. Comparethe results.

Regards

G

Actually, it is not possible to say exact reason. It may be several reasons. What is the length of you column. I faced this problem, because my column is 105 m length. First, increase the carrier gas pressure up to some extend than this and run one sample. It may be solve.

Grzegorz Boczkaj thanks for your answer

we have done both cases but it didn’t make a differences!

B.K.K.K. Jinadasa thanks a lot for your help

as I said the length of our column is 60 m.

and are you sure the problem is related to carrier gas pressure? ( we got good result with same method at first)

Mehrdad,

According to our todays correspondence on different GC topic,

If you used other channel in your GC and thia column remained in the oven without a carrier flow, this is posaible reason of your peak tailing and you can't do anything with that.

What you can try to do is:

-make a Grob test and check for what type of compounds it take place - is it a universal or "specific" behaviour

- conmect the column to a pump or reservoir with methanol and rinse the column slowly with 200-500mL.

Check also other solvents that are compatible with your column.

Regards

G

Grzegorz Boczkaj thanks a lot for your time that spend to help us

I'm going to do what you said and I'll let you know happened

Best regards

Mehrdad

Bake out you column at a higher temperature like 250-300 Celsius. You may also have injected excipients (crap) on the column when you injected the sample.

Looks like you may have oxidized the Wax phase of the column. This could be due to impurities in the carier gas or even a leak in the plumbing for the carrier gas. Was the nitrogen carrier gas pure, >99.999%? Is there a purifyer (to remove residual oxygen) in line with the carrier gas and is it still working? Did you store the column at a high temperature (>110C) over the months period of time? Did you bake out the injector while it was still attached to the column? Polyethylene glycol phases (Wax) columns are subject to thermal degredation. Also possible are impurities from the sample retained in the injector liner. It looks like you have linoleic acid in your samples, analytes like this polyunsaturated fatty acid are prone to polymerize at higher temperatures especially in the presence of oxygen. Is the injector liner dirty, or does it need to be replaced? I suggest you try a fresh injector liner, if that doesn't solve the peak tailing then try another column.

Bruce Levison thanks for your time

we've done most of hint that you said like changing the liner, septa, conditioning at maximum temperature that suggested for our column, trimming and ...but it didn't make differences.

As you said, I think the oxidation was happened because we don't have any traps for remove residual oxygen and moisture from our carrier gas. most probably we must use another column ...

Could be impurity of carrier gas or the solvent of sample. Additionally, loaded more samples continuously make like this kind of problem.

Hi Mr. Mehrdad Rabbani

Have you tested the instrument with a GC performance test mixture on a new column (or a different column in good condition) to make sure that all parts of the system (including carrier gas) work properly?

H. Liu

Hi Hanghui Liu

no we didn't test another column because we don't know exactly where the problem is and maybe it happen with our new column again.

Wax columns are highly polar and they are very temperature sensitive. Trace amounts of oxygen in carrier gas can oxidize the phase. You can try any standard sample on this column and check the peak shape. Even after conditioning and taking all other precautions, the peak shape does not improve, then it is possible that the phase has undergone degradation. In that case it is better to change the column. It is very important to have suitable filters in the carrier gas line.

Hi Mehrdad

optimize gradient ratio, check the temperature, flow pressure.

the best way is purging the column for long time.

if not, then change the column.

I agree with Bruce; it definitely looks like phase degradation. Stabilwax, despite the name, isn't all that stable. You have a hard ceiling of around 260 C before you start to cause degradation, especially in the presence of oxygen or moisture. If your samples are acidic you can also run into problems. You have to change wax phases much more frequently than, say, a polymethylsiloxane phase (like a -1 or -5 type phase). You have clearly lost resolution for these compounds. Sometimes cutting off 3-5 meters will give you back a usable column (you have to readjust your carrier) but many times wax phases, when gone, are gone for good.

See this video;

https://www.youtube.com/watch?v=GDfsNH4qbcE&feature=youtu.be

Work out on temperature programming, flow pressure.

the best way is to go for condition of GC for long time.

if not, then finally change the column

Dear M Rabbani,

I'm agreed with H Liu, because by GC performance test with test-mix, the chromatogram of test-mix tell you that which part of the instrument get affected. Therefore when you find out that your GC provide something unexpected data, then without any thinking inject a test-mix and interpretate the chromatogram by AMDIS, it easily solve all the problem you faced.