Chromatography Forum

Thank you both for the new advice.

I will try increasing the injector temperature and see what happens. Other than that I would like to keep the analytical conditions the same, as we look at a variety of analytes on this column (not just alkanes) and changing the method would be detrimental to other analyses.

Other than that, it sounds like the column is the only possible site of activity. Next time the instrument goes down for service I will trim the column head and replace all the ferrules. Hopefully that will help.

When you replace the ferrules be sure to cut 2-3 cm off the ends of the column after you have threaded then through the ferrule to get rid of any little shavings.

Peter

That's a good tip. Will do!

Hello!

Maybe this could help you.

If you don't trust the link, look for 5988-6191EN.

https://www.agilent.com/cs/library/post ... 6191EN.pdf

Regards

Hello!

Maybe this could help you.

If you don't trust the link, look for 5988-6191EN.

https://www.agilent.com/cs/library/post ... 6191EN.pdf

Regards

This is a very handy resource; thanks for that. According to the section on peak tailing, I think column activity is the main issue I have as the others would be affecting other peaks apart from just these alkanes.

I recently trimmed both ends of the column and replaced the ferrules and nuts on the injector and detector ends. It looks like the tailing has improved a lot but there are still tiny tails on the sample compounds. Ideally I would like these peaks to be perfect but the tailing is only minor so I will leave it at that.

This is what the peak bases look like up close: http://imgur.com/a/SYLKy

An update to this. I just replaced the injection port liner, septum, and trimmed the head of the column and the tailing is still present. If anything it is worse than the last image I posted.

Tetradecane is very good however peaks eluting after that are tailing noticeably.

Could this be caused by a poor column cut? It's the only thing I can think of as all of the injection port parts have been replaced.

Image here: https://imgur.com/8Muztju

Is this with the inlet temperature at 300C ? What type of inlet liner do you have, and does it have any packing in it ? When you trim the column, how much do you take off ?

Peter

Is this with the inlet temperature at 300C ? What type of inlet liner do you have, and does it have any packing in it ? When you trim the column, how much do you take off ?

Peter

Hi Peter.

Inlet was at 250. I use Topaz split liners with glass wool packing. I trimmed about 3 cm off the column.

There was a suggestion earlier to increase inlet temperature to 300C. Did you try that ?

Trimming 3 cm will not help, take off about 30 cm.

Peter

Dear,

Please do following.

1. Check inlet temperature it should be around 300 C
2. Check appropriate septum purge flow should be around 3 ml/min
3. Appropriate column gas flow
4. Increase split ratio or decrease sample size ( Injection volume )
5. Appropriate makeup flow around 30 to 40 ml/min

I just realised that I forgot to follow up on this.

Dear,

Please do following.

1. Check inlet temperature it should be around 300 C
2. Check appropriate septum purge flow should be around 3 ml/min
3. Appropriate column gas flow
4. Increase split ratio or decrease sample size ( Injection volume )
5. Appropriate makeup flow around 30 to 40 ml/min

I have set the inlet temperature to 300, septum purge flow to 3 ml/min, column gas flow to 1 ml/min, split ratio to 25:1, injection volume to 1 ul, makeup flow to 29 ml/min.

There was a suggestion earlier to increase inlet temperature to 300C. Did you try that ?

Trimming 3 cm will not help, take off about 30 cm.

Peter

Yes, inlet is at 300.

I am still getting tailing peaks - the same as in the previous picture I uploaded. I take it that I just need to trim more length off the head of the column?

You need to take off 30 cm when you trim the column.

Peter

You need to take off 30 cm when you trim the column.

Peter

Hi Peter,

Yes I will try that next. Just wanted to be sure there was nothing else that could be contributing.

An update on this. We just moved the GC so I took the opportunity to trim the column and do some other maintenance. I trimmed about 1m from the tail and the head of the column. The tailing is still present. Slightly better, mind you, but still present.

Could the tailing be an issue with poor column cuts?

Where is the glass wool located in your inlet liner? Is it near the top, middle, or bottom? Near the bottom is where it should be. Also, is your pressure program set for constant flow or constant pressure? For the heavier analytes, you'll want constant flow.

Where is the glass wool located in your inlet liner? Is it near the top, middle, or bottom? Near the bottom is where it should be. Also, is your pressure program set for constant flow or constant pressure? For the heavier analytes, you'll want constant flow.

I'm using liners that come pre-packaged with wool. It sits near the middle, slightly closer to the top. Do I need a different style of liner? I am using these: http://www.restek.com/catalog/view/49269

The GC program is set to a constant linear velocity.

Hi

Simple fixes :
Increase final temp of program
Increase temp of inlet
Decrease column thickness
Overloading or split ratio a possibility
Injection too long perhaps but this is a long shot