USP tailing problem

[Sandro]

Hello Everyone
My lab is currently trying to get a water method that has been used on a 5890 to work on a 7890 GC, but are having some problems with tailing on the first peak. We use a double tapered gooseneck liner on the 5890, but have tried a couple of different liners on the 7890. The only reason we have not kept to using the double taper liner on the 7890 was because our RSD (needs to be at 5% or lower) was failing. Our RSD was in the upper teens. If we used a 4mm liner with wool, our RSD passed but the tailing on the first peak was around 1.7-2.2, when we need it to be below 1.5. I have also used the following liners, low pressure dropliner with wool and gooseneck splitless liner, to no success.

Here is some information of how the 5890 is setup:
Column: Wax 15m x 0.53um from J&W
Double taper liner
Injection volume: 1uL
Injector: 210C
Detector: 250C

We have tried a lot of different things on the 7890 to fix the tailing problem, but nothing seems to help. We have tried a 30m column with a higher pressure, we have tried injecting just 0.5uL, we have increased the split ratio, we have decreased our initial oven temp.

I am hoping someone can help guide me in some sort of direction.

Thank you very much
Sandro

[Peter Apps]

What are the analytes ?, which of them tail ? It would help if you could post a chromatogram - instructions are in a sticky at the top of the LC page.

Peter

[Sandro]

Hi Peter
We are analyzing Ethylene Oxide, Ethylene Chlorohydrin, and Ethylene Glycol. The Ethylene Oxide peak is the one that is having the tailing issue. I scanned a couple of chromatograms and I hope they came out ok. Not sure how clear they are going to be. If there is another way to get just the image of the chromatogram, please let me know and I will try to do that instead.
This chromatogram was a 0.5uL injection of one of our standards.


This chromatogram was a 0.5uL injection of another standard.


I hope this information helps.
Thank you.
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[Peter Apps]

The chromatograms are not all that clear, but I can see that you have a lot more resolution than you need, and if the standard is a refelection of concentrations in real samples, lots of sensitivity. As a consequence you could relax the peak tailing requirement and still get results that were fit for purpose.

What solvent is your standard and samples dissolved in ?

As you have seen, if you add glass wool to the liner you get tailing, due to adsorption. If you take the glass wool out you get poor rsd due to inconsistent sample vaporization. So the trick is to get consistent sample vaporization without glass wool. There are a host of fritted and baffled liners you could try, also put a pre-injection dwell on the autosampler, in a lot of cases the fast cold needle defaults on Agilents are not optimal.

The tailing could also be due to active sites on the column, cut about a meter off the inlet end.

Peter

[Sandro]

Hi Peter

We use water as our solvent.

Thanks.