Chromatography Forum

Help! I only need to run one compound on my GC and it tails badly. Everything else looks great!
My butanedione and pentanedione both tail badly on my column. I can run other stuff like alcohols,
ethers, aromatics and they look beautiful!

Running 6890/5973 MS and FID using split. Identical tailing at both detectors and at 10 and 1000 ppm.

Column: Agilent DB-624, 30M x 250um x 1.4 um thick. 43 cm/sec He. 1 uL injection (fast) in acetone.
Splitless injection; liner is deactivated 4 mm tapered with quartz wool.
40C for 1.5 minutes then 20 C/min to 200 C.

Inlet temp: Normally 250. Tried 200 and 160C. No effect on tailing.
Trimmed 2 feet on head of column. No effect on tailing.
Changed liner. No effect on tailing.
Cleaned liner assembly with gun brush and solvents. No effect on tailing.

Anyone have any thoughts on what else I could try?

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It looks like solvent effects to me - you a probably getting solvent condensing at the head of the column and distorting the chromatography of the two ketones. BUT - is this split or splitless ? "Running 6890/5973 MS and FID using split." vs "Splitless injection; liner is deactivated 4 mm tapered with quartz wool".

Is the test mix also dissolved in acetone ?

The vertical scale on the ketones and the test mix is drastically different - what do the test mix peaks look like if you expand the vertical scale to match the ketones chromatogram ?

Try increasing the initial temp of the column programme to 60C - if you can get rid of the distortion you have separation to spare, so no need to start at 40C.

Peter

Oh yeah. It is splitless.

both dissolved in acetone

Showing FID and MS so vertical scale is very different. Peak shape remains constant regardless of scale, detector and concentration.

Even at 40 the acetone tail extends into the diketone peaks when viewed by FID.

If you inject a larger concentration of the diketones and run split, does the tailing go away?

Oh yeah. It is splitless.

both dissolved in acetone

Showing FID and MS so vertical scale is very different. Peak shape remains constant regardless of scale, detector and concentration.

Even at 40 the acetone tail extends into the diketone peaks when viewed by FID.

What is the splitless time, in other words when do you open the split ?

Try starting at 60C and programming at 5C/min instead of 20C/min.

Peter

I always use a wax column for diacetyl, acetoin, acetyl valeryl, etc. They always look atrocious (same as small carboxylic acids) on a db-5 and a 624 might also not be polar enough.

In do diacetyl with full evaporative headspace GC/MS SIM with acetonitrile as the ITSD on a wax column and my LOQ is 10 ppm solution in headspace vial (7.5 ul in 9ml headspace Tekmar 7000)

Diacetyl ALWAYS has a terrible peak shape due I thought to the unstable chemical structure. However, a slightly better peak shape was found using the 50% Phenyl methyl column.
Also, if any solvent with active protons are present you will find issues.
Good luck, because if it were easy, anybody could do it.
Rod

Cryofocusing will take care of this issue.
Consult this document:
http://thecleanvape.com/wp-content/uplo ... yBerry.pdf

Cryofocusing will take care of this issue.
Consult this document:
http://thecleanvape.com/wp-content/uplo ... yBerry.pdf

If the problem is due to solvent effects then cryofocussing will probably make it worse.

Peter

What is the oven temperature program. It could be solvent effect.