tailing peaks

[edmgc7788]

Hi, everyone
i am using 7890a GC FID, with temperature programme. My initial temp is 40degree, injectior 350, detector 360.Column is DB-1.
recently both column solvent peak is tailing. I change liner, gold seal and use brush slightly clean inlet,then i use lots cotton stick with methanol to clean. However, then tailing didn't getting better. I think my column installation is good.
any suggestions? please help me
thank you
rebecca

[Consumer Products Guy]

Remove column at inlet end. Cut off 1/2 inch of column, set to correct penetration depth (like 4mm) and reinstall into inlet. Solvent tailing is typically due to column inlet installation.

Are your split flow and septum flow set correctly?

[aldehyde]

Also check the split vent line and the part it screws onto (on the inlet.) Did you see any residue when you cleaned the inlet with cotton swabs? If there was contaminant on the walls there may also be contamination in the split vent line. I agree with CPG, trim a bit of the column--active sites are usually on the liner and the first inch or two of column.

[edmgc7788]

Thank you very much to answer my questions. Both column(back and front) i was using for 2 months. Just recently after i change the liner, the tailing is getting worse. So, for some time, i always think about it's the liner problem. And one week ago i ran dirty samples, but i change gold seal, liner, trim the column. I am very frustrated by this problem. I will check the split vent line to take a look.
thanks again
rebecca

[jdezeeuw]

Hi
I agree installation is main problem. But split flow must be working also, and it needs to be at least > 1:5. Many of us do trust the GC readouts which can be wrong. Split lines can get blocked, same as split line filters. Check real the split flow using flow meters. If that is OK, we always use methane as a sample to see if installation is good. You need to see a sharp symmetrical peak. If this peak is OK, then you know installation should be fine.

Now if we inject solvent there still can be several issues causing tailing:
- is your injector hot? (check yourself.. also here don't "believe" your GC readout!
- is your solvent polar? If you use methanol, it will always give some tailing;
- is your column not activated? cutting a 20 cm section form inlet will tell you that.
- is your detector position OK? column should be close to the flame tip.
- also, if you use a coupling, many tailing problems happen within couplings due to improper column positining.

Don't forget to check for leaks using leak detector; once you have "sharp" peaks it does not mean there are no leaks. Leaks will cause activity, but usually only when analysis temperatures are >150C

rgsd

jaap de zeeuw, Restek corporation

[Mike H.]

I had a terrible time with tailing peaks for the polar solvents like MeOH using DB-1, and RTX-624 column from the USP residual solvents method. I was never able to correct this. I ended up switching to a wax column and the tailing problem was gone.

[chromatographer1]

Your entire column might be contaminated after running dirty samples.

It happens.

I am sure you know the solution.

and yes, they are expensive. But, so is life.

best wishes,

Rod

[jdezeeuw]

agree.. next generation column technology is showing much better performance for polar, acid and base-analyte. Walt Jennings taught us this was the way to go in 2004. Restek started with a series, Agilent followed also. We have to keep Dr Gauss happy, also for more tough analyte.

[Mike H.]

It's ironic that there's already a tailing peaks thread. I just encountered an unexpected instance of tailing peaks. I'm hoping somebody can help me understand what's going on.

Background I have been using a headspace method using a DB-wax column to assay Meoh,ACN and IPA. Recently I was told to try to add N-methylpyrolidine to the mix. The response for this was poor using DMSO so I tried water, but the precision was terrible. The HS oven temp was set to 80°C, but I guess the water was creating problems so I scraped this idea.

I decided to try a direct injection method using the exact parameter minus the headspace portion and started seeing some tailing on MeOH and ACN. Can just the change from headspace to direct injection cause tailing? Or do I have a possible contamination issue ie. liner etc like the OP? thx

[jdezeeuw]

If headspace (with splitting) already gives a tail, any other sample evaporation technique will be more challenging. I also do hope that when you say "direct" injection,. you still mean that you are splitting.

Real direct injection (without splitting) will always give you a tail on the components that elute early in the C'gram

[chromatographer1]

There can be many reasons for tailing. First, if you can study WHY tailing happens then you may be able to determine the exact reason why you are getting tailing in your experiment. That topic is too long to discuss here but in short, the equilibrium of an analyte plug not ideally achieved and the backside of the 'plug' remains in the liquid phase longer than the front of the plug. Active sites, low pressure of the vapor phase, the width of the carrier solvent affecting the interaction of the analyte with the column phase are all possible causes of tailing, and there are many more.

Years ago when I had tailing of methanol on a 624(1301) column I tried increasing the pressure (and the flow) and was not happy with the results of my headspace chromatogrqphy. I put a short piece of Wax column ahead of the 624 column and was able to focus the plug so the tailing was eliminated at the low temperatures (40C) I was using. Still the methanol was broad and had some tailing.

Then I also used a restrictor column attached to the column tail which increased the head pressure at the column while keeping the same flow. That solved my tailing.

good luck,

Rod

[Mike H.]

Good stuff Chromatographer1. I've never used a restricter capilliary, but I can probably order one if necessary. I could try to increase pressure and see what happens. Currently it's set at 3.4 psi and the column dimensions are 30m x 0.53 x 1.

Then I'll change the liner and see what affect this has. This is so weird though. All parameters are exactly the same for both the headspace and direct injection methods. The only difference between perfect peak shape and tailing peaks is injecting sample as gas via headspace and injecting as liquid via direct injection.

[Mike H.]

Turned out to be the liner. I was using a Agilent 5183-4647 liner which looks like this http://www.chem.agilent.com/en-US/Store ... =5183-4647 It produced a 2.2 tailing.

I switched to a http://www.chem.agilent.com/en-US/Store ... 6(Agilent) liner and the tailing improved to 1.5 which is acceptable.
Now I'm curious if the taling would improve further if I used a liner with no taper?

[tlahren]

This seems like a single taper (gooseneck) liner for split-less injections. Are you doing a split or split-less injection? What split ratio if so? I'm not sure what effect a tapered liner would have on a split injection but I have never used them for it. I am using mostly pulsed split-less injection for semi- to non-volatile compounds.

Just curious, what compounds are tailing? All or just specific compounds?

[Mike H.]

It was a splitless injection on a DB-Wax 30m x 0.53 x 1.0 column. Analytes were MeoH (tailing) ACN, IPA, NMP.