soliciting comments on 1988 article: aldehydes & ketone

[khirth]

I am analyzing chlorinated aldehydes and ketones. Tried lots of different column manufacturers and phases. (Sometimes seems the grossly tailing peak shapes are dependent on moon phase.) Found this article: J High Resol Chrom. & Chrom. Communications by L.J.anthony, et al: Interactions of aldehydes and ketones with the surface of Fused Silica Caillary Columns." The article contrasts conventionally-prepard vs miodified vapor deposition process columns and their comparative amount of bonded silanols. Question 1: is anyone familiar with the articel and have comment? Question 2: does anyone have suggestion as to what type & phase column would be most rugged and give best peak shape for the aldehydes and ketones? Any experience in this area?

In advance, much appreciated!

[GOM]

Hi,

I suspect that, with modern columns, the tailing that you are seeing is down to other factors, particularly if it is varying as you imply.

Can you tell us what phases you have tried and what the matrix is that you are injecting. I would have thought that a polar column (e.g. Innowax) would not have given you any problems.

Regards,

Ralph

[Peter Apps]

Welcome back !

I'm with Ralph in that modern capillary columns are very unlikely to cause tailing of carbonyls - I'm not sure what the effect of chlorination would be though.

Are you still using the wax column ?, has there been a deterioration in performance ?

How bad is "grossly tailing" - can you post a chromatogram (instructions in a sticky at the top of the LC page) ?

What quantity of analyte is there per peak ?. Do other compounds (at similar quantities) also tail ?

Peter

[khirth]

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Top chromatogram is Grob mix. (Nonanal not observed.)
Next is TIC (notice siloxane peaks getting progressively broader.)
Next 3 are extracted chromatograms (Notice grossly reduced response and tailing peaks)

Concentration are ~3 ng/ul in acetone using 1 uL splitless injection.

Columns tried are SGE SolGel-1, Rxi-5ms, ZB-1ms, VF200 and this is brand spanking new (conditioned per instructions) SGE SolGel-wax.

Inlet liners tried are Siltek metal single gooseneck, unpacked and Siltek glass double gooseneck, unpacked. Neither appears to be better than the other for these analytes.

Thanks in advance.

[Peter Apps]

Where are the siloxanes on the second chromatogram coming from ? You inject a standard and the biggest peaks on the chromatogram are silicone breakdown products. Which column was this done on ? Why are there no siloxanes with the Grob mix - both are TICs ?

If I recall you are using an ion trap, so the single ions are extracted from the TIC. How does the Grob mix look in SIM ? A conceivable (but not likely) cause for low SIM response is that the MS mass calibration has drifted, or that the mass window is set way too low. This would not make the peaks tail though.

Can you give us all you operating conditions again, thanks.

Peter

[khirth]

Thanks for your responses. I have been changing columns and liners.

The previous chromatograms were run on a WAX and on a ZB-1. My Grob mix is in hexane and much more concentrated than my samples. My samples are in pesticide grade acetone.

There was some previous discussion about acetone degrading modern columns. Jury was out on that matter. I do not believe acetone in and of itself degrades the columns. Maybe, however, what the acetone drags in with it... but that's iffy since it's pesticide grade.

Since my last posting, I discovered that my samples appear to be stripping off the Siltek coating. (Siltek is the indert coating on the Varian 3800 injectors too.) Restek tech service confirmed that the liner's color change (from purplish-blue to yellowish) indicates removal of the Siltek from the metal single gooseneck liner. I'm waiting for a call back as to what might be its cause. Suggestion was high pH, but that is not the case with my samples.

My sample thus far is simply an acetone solution of chlorinated: vanillin, syringaldehyde and p-OH-benzaldehyde. No extraneous substrate, etc.

The mass hasn't drifted. Scan range is small (100-250), but not SIM because 1 want to see the isotope pattern with the characteristic aldehyde loss of 1 from each (M & M+2).

I switched from the WAX to the non-polar column because I wanted the least bleed possible. Also because the WAX appeared to have degraded. somewhat improved, but not much. Am expecting arrival of brand new columns tomorrow. (Restek Rxi-1 and Rxi-wax.)

I will also have acetylation of the 2-Cl-syringaldehyde finished tomorrow. I will run the acetylated and non-acetylated side-by-side (both will be chlorinated but the phenolic will be removed.)

Will report back. Until then, have you much experience/knowledge of Siltek and stripping off of the deactivating coating?

[Peter Apps]

I have some experience with glass deactivated by silicon deposited from the gas phase and it is as tough as old boots !, In my experience the only thing that attacks is strong aqueous alkali, the coatings that I made could be baked at 400 C in air without changing appearance. Anything that attacks Siltek will certainly destroy your analytes as well. It would also account for the siloxane peaks that you see, and the rapid deterioration of the columns - your samples ( and standards) seem to contain something that is strongly chemically reactive.

For the Grob mix to be useful for troubleshooting you need to run it at the same concentration as the samples, and dissolved in the same solvent - dilute the hexane based mix in some of the acetone.

Have you tried acetone from a different supplier ?

Peter

[khirth]

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[Peter Apps]

You definitely have some adsorption of the chlorophenol, which might be causing problems, but every peak on the chromatogram is broadened and tailed with the exception of the pentadecane. When alkanes tail and broaden it points to absorption or dead volumes. It is possible that there is a bit of crud stting in the injector (probably a fragment of septum) or a bit of crud stuck in the column - I have seen ferrule fragments carry nearly a metre into a column. Dead volumes are unlikely as long as the column is inserted to the right depth in the inlet and the detector. Given the attack on the siltek it is also possible that the phase in the column has been made uneven. Why pentadecane is sharp and the lighter alkanes tailed is a puzzle, it might be related to inlet temperature and column programme.

Since this column and inlet are sick anyway, you could inject some of the current acetone at a high split ratio and use the MS to identify it and any possible aggressive contaminants.

My advice is, when the new column arrives do NOT try it with anything containing the current acetone, wait until the new acetone arrives. Change the inlet liner as well before you use the new column. When installing the new column be sure to cut 50 mmm or so off the end after you have threaded it through a ferrule.

Good luck

Peter

[khirth]

Injector temp is 275C. Splitless 0.5 min with press pulse 20 psi. (Tried with and without press. pulse: observed no difference.) Oven program: 80C hold 0.5 min, ramp to 130C at 50C/min hold 1.5 min, ramp to 180C at 4C/min, ramp to 320C at 90C/min. However, have begun omitting last clean-off ramp due to too much siloxane garbage.

New column did not arrive today. Maybe early next week.

Did make up low std in both acetone and MeCl2 to see if any improvement with this column w/o acetone. Made no difference. Suspect things have deteriorated beyond repair with this column.

Have been using siltite ferrules for a while - precisely to avoid any potential problems due to graphite particles.

The Varian 3800 injector design is such that it can be swabbed out from the top, but not reamed through. (i.e. it has no removeable gold disc at its bottom.) So, other than using a solvent-moistened swab to wipe the inlet from the top, do you have any suggestions about approaches to ensure no particles are stuck in it?

I could force a stream of Argon into the inlet, but I don't know what it would accomplish and I don't want to risk shoving something back into the carrier gas lines. Ideas?

Again, thanks for the suggestions. They are appreciated.

[Peter Apps]

To get at he bottom of the inlet, unscrew the three screws that hold the flanges on the inlet body just inside the top of the oven, the bottom of the inlet will then come off. There is a gasket to seal it that you will probably need to replace when you reassemble, a spare one should have copme with the GC.

Even with the fanciest ferrules you still need to cut a piece off the end of the column after you have threaded the column through the ferrule.

I am really curious to know if the acetone is really acetone, and if you can find any aggressive impurities in it.

Peter

[Peter Apps]

Any progress ???

Peter