packed column peak area reduce

[sg]

Hi guys,

I am currently encountering a problem when using packed column (15% FFAP, 1% phosphoric acid, 100/120 chromosorb WAW stainless steel column) to test pivalic acid.

However, the peak area of the standard reduced half compared to the typical value. We try another GC instrument and on 3 other new column and still can not get it and even sometime for some injection, there is no peak area detected....

Can you guys share your experience with me what I shoudl do?

Thanks!

[Don_Hilton]

A few questions:

What detector are you using?

If you inject something like butane or pentane do you see a peak?

What solvent are you using?

[sg]

Hi,

FID is used. The sample is extracted using the diethylether and this is injected.

[Peter Apps]

Check for leaks and change the septum.

Does the retention time change ?

Peter

[AICMM]

sg,

Try a new standard. You say another GC and 3 new columns, so the problem is probably not the GC but rather the standard. Do you get the same peak for diethyl ether?

Best regards.

[chromatographer1]

Where did you buy the columns?

Have you conditioned the columns? If so, what were the temperatures and the flow rate and the carrier gas used?

Are the metal columns in 304, or 316 SS, or perhaps you bought them in nickel ?

What kind of glass wool did you specify when you bought the columns?

The problem is probably with the columns. There are many things that can go wrong if you specified or you got the wrong materials.

best wishes,

Rodney George
consultant

[sg]

Some more detailed information:

1. The column is stainless steel pack column,
2. To run the test, we prepare a resolution solution of 1% pivalic acid and 1% propionic acid in diethyl ether. For standard solution, it is 0.5% pivalic acid in diethyl ether.

3. The peak are in resolution solution is about 3000 for pivalic acid; however, in the standard it is only about 200 and sometimes increase and sometimes decreased bit. Theoritically speaking, the area should be about 1500 since the concentration is half as the resolution.

Me really don't know what happen, please help!

[chromatographer1]

SG

I would like to help you but if you can not give additional information about the problem I don't think anyone will be able to assist you other than listing a long itemization of everything that can possibly go wrong with the instrument or the column that could give you the results you describe.

I suggest you go to the vendor from which you bought the columns and ask for help or replacements.

Good luck,

Rod

[Don_Hilton]

1) when did you last do inlet maintanance? (How old is the septum)
2) what temperature are you running the FID and are the air and hydrogen at the vendor reccomended flow rates?
3) are you injecting manually or using an autosamper?
4) do the retention times change?
5) If you make an injection with something that will not be lost to actve sites (like some parrafins) do you have the same kind of response problems?
6) Are this GC and column used for any other kinds of analysis?

My thinking here: something like 80% of GC problems are with the inlet system. Very often a leaking septum is a reason for loss of sensitivity (by sample escaping from the instrument!).

Active sites in the inlet or column can be a problem (and yes, with a packed column - you do not have the complex inlet that you find in capillary). Garbage on the glass wool can mess up an analysis - or failure to use deactivated wool - or handling deactivated glass wool too roughly, and breaking it up a bit to give lots of active surface, can also mess up an analysis. So a check with compunds not llikely to be affected by active sites can help here.

FID conditions and temperature - in fact all of the parameters need a check. Someone, who I will not name - lest I embarass my self - has been known to quickly fix a parameter and then discover that whatever got entered into the instrument went somewhere else - only because the intended parameter did not get changed. Small errors like this can only be found by sitting down with the method parameters and checking them all.

Check gas flow into your instrument. Be sure that you have pressure at the back of the instrument that is at least 20 psi over the regulated pressure in the instrument. Regulators need pressure across them to work properly. I've seen a lab with adequate pressure at the cylinder, but about 10 to 15 meters of 1/8" tubing running from the cylinder to the instrument - with various T's splitting gas flow off to other instruments. Long story short. The instrument at the end of the line was starved.

Retention time changes indicate a problem in the instrument. And if they are varying, we need to ask more questions -- but know where to ask.

And the question about the instrument being used for other kinds of analsis -- given the nature of the compunds you are trying to analyze, residues left on the head of the column from other kinds of samples could affect your analysis.

And last question, while I am thinking of it:
7) Have you protected the samples from evaporation - multiple injections from the same autosampler vial over time will result in a change in the sample. The ether will evaporate through the punctured septum.

Let us know
Don

[AICMM]

sg,

You are shooting 0.5% of a component in diethyl ether on a packed column on an FID and you are getting 3000 counts. Assuming a one microliter injection, that is something like 5000ng on column with no split. That is a terrible response for an FID. Is that what you used to get or has your sensitivity plummeted? A quick test on column versus detector would be to make a 5000ppm standard of some other inert compound like isooctane and run it and see what kind of response you get. If high, probably column, if low (like 3000), probably detector.

Best regards.