rounded peak and tailing on GC-FID

[Ceomgenus]

In the lab, we have a Shimadzu GC-2014 with an FID detector and dual packed-column injector. My job is to get the machine operating well so that it can be used. For quite a while now, I have been having a problem with rounded peaks and tailing. The sample I am using is methane in nitrogen. I have re-installed the injector and the column, but without any difference. I have been trying different flow rates and temperatures, but without and difference there either. I am thinking it could be my injection technique, but I have been using the method described elsewhere in the forums: insert, count to three, depress the plunger, count to three, remove. Below is a picture of the kinds of "spikes" I have been getting. Thanks for any help you can offer.

[AICMM]

Ceomgenus,

You have a 7 minute long methane peak starting to elute at 10 minutes into the run? Methane, on every column I can think of, will come out much faster than that and generally much sharper. Could be lots of things including almost no flow or you are not looking at methane. Please post more information about your set up including columns, column flows, column lengths, head pressure, oven temp., standard conc., etc, etc....

Best regards.

[Ceomgenus]

The column is an RT-QPLOT, 30m long, .53mm inner diameter, and 20um film thickness. The flow rate for this run was 10mL/min. with a pressure of about 125 kPa. The injector temperature was 50C, the column was 40C, and the FID detector was 250C. I have tried different flow rates, and the higher ones do give give an earlier peak which takes less time to elute, but the general shape is the same - rounded at the top and trailing off for quite a while. The sample is made of 100 torr of methane in 900 torr of nitrogen. Thanks again.

[AICMM]

Ceomgenus,

The flow rate for the column, is that measured or calculated? How much did you increase the flow rate on the other experiments and how much earlier did it push the methane?

Increase your injector temp to 125 or 150, no need to let water pile up there.

First thing is to get methane to come out where it is supposed to, then we can work on peak shape and other issues.

Best regards.

[Ron]

Did you measure the flow rate at the end of the column? If you are getting 10 mL/min out of the column you have a massive leak, which is probably the cause of the late retention time and bad peak shape. 125kPa should give you a column flow of approximately 37 mL/min.

What liner are you using? It should be a wide bore insert.

Have you called the Shimadzu toll free tech support line or your local sales rep? If this is a new installation call the local sales rep and ask for help, there is phone support and field technical support available to help resolve problems like this.