Glycols - broad peaks

[mbdixon]

https://www.restek.com/pdfs/EVAN2873-UNV.pdf

Hi I am trying to replaicte the attached method...but I'm struggling with peak shapes and thus sensitivity at low levels. My GC is a Agilent 7890 and have a MS and FID attached with a splitter. The only other variances from the method is that I am iusng an Agilent liner (5190-3165 split, tapered with wool) and my column is Zebron ZB-WAX plus (30m x 0.32 id x 0.25µm film), with a guard column

I have changed the liner, septum but not tried the gold seal yet, although it is fairly new.

My first thought is the fact the film thickness is significantly less, is a column with a thicker film the next thing to change? Obviously a relatively expensive change!

[AndyA]

I would try using a different liner first. the liner your using i think is a closed liner so narrow on the column end?

The method you've quoted uses an open liner. The closed liner focus your sample more on the column (and tend to be used more for splitless injections) add to this the column your using is more narrow (0.32mm instead of 0.53) and a quarter of the film thickness. Your placing more sample on a smaller area.

You could also try adjusting the split ratio and injection volume before looking at another column.

[James_Ball]

As Andy said, the smaller diameter column will overload with less analyte on column than the 0.53 will. You can either inject lower concentration standards or increase the split ratio to compensate. The 0.32 column should give a little lower detection limits so you can increase split ratio and still achieve the same sensitivity.

Also there are differences in composition of the different Wax columns and shown in the last chromatogram in the link you posted. It could be the Zebron is not giving as sharp of peaks because it is a slightly different stationary phase. The column phases have become quite specialized even within the same phase name like "Wax" or "xx5" ect. Restek makes the Rtx-Wax, StabilWax, StabilWaxDB(for basic analytes) and the StabilWaxMS for low bleed MS work and each has a different retentive property. I imagine Phenomenex has different Wax phases also so you may want to look at that after you try a different liner and split ratio.

Also what guard column are you using? It needs to have a polarity that matches your solvent, so for water it needs a polar deactivation layer or the water will form droplets inside the guard column instead of a uniform film coating. Reference #5 in this FAQ for water injections and guard columns https://www.restek.com/Pages/faq_gcc

[Consumer Products Guy]

I didn't like injecting 1 microliter of water, ever, it expands way too much. Try 0.5 microliters or less, and consider a smaller syringe too.

[mbdixon]

Thank you everyone for the advice. I haven't had chance to try any of this yet, but I have found an old Varian CP-WAX column in the back of a cupboard (60m x 320 x 0.5). Hopefully this will do the business!

I'll see what this does and report back...

[Bigbear]

I agree with a 0.5 ul injection, also lower the injection port to 120C.

[mbdixon]

Thanks for all the responses, and sorry for the tardy reply - all very illuminating! Saying that in the end, I did have to buy a new column which worked a treat...

[Consumer Products Guy]

I worked in industry, and I made it a practice to ALWAYS have a spare, new column on the shelf so I could swap it in if necessary for such troubleshooting.

We also copied chromatograms made on new columns inmto our test methods, so we would have ready reference as to what good chromatography would look like.

Above was for BOTH GC and HPLC (and GCMS).