Another FAME question

[bi0hazard]

Hi! Here at the lab we want to quantify the FAME using GC/FID. We are using SP-2560 column. I'm not new to GC but i'm a newbie in FAME analysis. We're using a standard from another plant like us.

Here is the GC setup:
Injection volume: 1uL
Split: 100:1 (Helium)
Oven: 140 C, hold 5 mins
240 C, 4 C/min, hold 30 mins.
Detector: 280 C
Injector: 220 C

WE are using an old Perkin-Elmer AutoSystem XL with autosampler.
You guys being FAME pros, what could we do to improve resolution and reduce tailing... Here are 2 pics:


We are getting this kind of chromatograph:

Small zoom:


Big zoom:



If you want more zoom, please let me know.

Thx

Tommy.

[mahdiebrahimi]

If you wanna achieve better resolution for your FAME try this method:

Oven: start 120 C hold for 5 min and then increase temperature 2.5 C/min until 220 C after that hold for 5 min.

I hope you can get better result

[Peter Apps]

The peaks are front-tailed, which points to concentration overloading. Try diluting the sample, increasing the split, or injecting a smaller volume, or a combination of any of these. Also make sure that the inlet liner is clean.

Peter

[bi0hazard]

Thx for the tips. I'm gonna try these today.

Also make sure that the inlet liner is clean.

A guy from Perkin installed and repaired all the GC to be ready and functionnal. I'm pretty sure he changed the liner on the 2 GCs.

I'll keep you in touch.

[Peter Apps]

Also make sure that the inlet liner is clean.

A guy from Perkin installed and repaired all the GC to be ready and functionnal. I'm pretty sure he changed the liner on the 2 GCs.

I'll keep you in touch.

Hi Biohazard

While it's not my place to tell you how to run your lab, you are going to be spending a lot on service calls if you use the agents to do routine maintenance like swapping liners. Depending on what samples you run you might need to change liners (and septa) every day.

Peter

[bi0hazard]

Yes i'm totally agree with you. The thing is, our plant is starting right now, so we don't have our brand new equipement yet. A guy from the company (the buyer...) bought many apparatus from a shutted plant in US... and we got 2 x 20 years old GC. The buyer doesn't know a thing about GCs analysis and lab apparatus, so he bought everything.
GCs are GCs, but me and my co-worker never worked with a GC that old. We did'nt know the actual shape of them.

And we needed a guy from Perkin to install the software and mount de computer to work with them, so he did a full maintenance on them.

Next time, we are gonna change the liners, sceptum, etc ourselves

[Peter Apps]

GCs that are old enough to vote might be a bit of a challenge to keep running. Kudos to you for getting a full set up before you started, and to your local P-E suppliers for being willing to support them. You did get new columns right ?

Peter

[HW Mueller]

You don´t have a reference chromatogram for this standard? Do you know what is supposed to be in it? Looks to me as if you have enormous amounts of dirt/decomposition. How many times did you do this? Did you do what Peter suggested, namely, inject less?

[bi0hazard]

GCs that are old enough to vote might be a bit of a challenge to keep running. Kudos to you for getting a full set up before you started, and to your local P-E suppliers for being willing to support them. You did get new columns right ?

Peter

Yes we bought new columns as well. SP-2560 for the cis/trans and a Restek RTX-1 (7.5m X .25 X .25um) for fast chromatography (in-process samples).

My supervisor is considering new GCs (Agilent). But still, we need to try to run those old GCs.

We ran through a lot of problems, like the "port comm error" caused by the second CPU of the computer. I've disabled it, and it solved the problem.

The guy from P-E didn't plan to work with that old equipement, he was a little bit discouraged.

You don´t have a reference chromatogram for this standard? Do you know what is supposed to be in it? Looks to me as if you have enormous amounts of dirt/decomposition. How many times did you do this? Did you do what Peter suggested, namely, inject less?

The standard we are using come from a similir plant in Pittsburgh (we are based in Canada). The supervisor from this plant is here to help us to mount the lab. I'll try to get the real chromatograph.
Yes the sample (std) is old (maybe 2-3 weeks) and there is a lot of decomposition, I agree. We are just trying to get good resolution and no more peaks tailing before going with another standard, and then, some samples.

This morning, I tried what mahdiebrahimi told me. We are getting better elution but still, need some improvements. I increase the Bunching FActor to 4 and noise threshold to 10.

Next step, inject less (0,5uL instead of 1,0 uL). If there is no change, i'm gonna dilute the sample. I'll post a new chromato when the inject less step will be done. Finally, if this isn't enough, we will have to wait for the Flowmeter to be delivered... I borrowed one from another plant near us to set up the GC with the SP-2560 column.

BTW, thanks all to support me working those GCs... Their giving me some headaches

EDIT: Might reconsider changing the seryngue. The one we are using isn't Gas Tight. I increased the injector/detector temp to 350 C to flush.
When i'm injecting hexane only, there is a lot of unknown peaks (suppose to be pure hexane). I'll check this.

[bi0hazard]

Here it is. I just reduce the injection volume to 0,5uL. Still getting front-tailed peaks.

Non zoom pic:


Zoomed pic:


Next step, dilute the std. But I don't know the solvent (yet). The Pittsburgh guy isn't at the lab at the moment. As soon as I get a shot, i'll post it here.

[Bruce Hamilton]

Fronting peaks can be caused by several other factors.

Some that I'd want to check:-
- gas flows are correct, especially split system and detector ( if there is a makeup gas, I'd try increasing it )
- capillary column is correctly installed in injector and detector.
- no leaks at injector connections or septum during injection or run.
- sample/standard solvent and injection volume ( but 220C injector should cope with most solvents ).

I'd want to run the column certificate test mix when installing a new column, just to ensure all is well.

[bi0hazard]

Helium flow is:
-about 2,40 mL/min at 50 C (60 psi) for a 100m column (using P-E chart)
-split flow is set to 100:1 with an ADM 1000.