Chromatography Forum

I have just installed a JAS UNIS programmable PTV inlet. I ran a hot splitless PAH/Phenol method that was identical to the one we have been running on the old agilent inlet and my phenols have gone nuts (some are splitting, all are tailing/smearing and some have disappeared altogether).

I suspect it is a liner issue as the column has been clipped and is fairly new, (although it was starting to lose phenol performance, it was not as bad as it is now) . I have tried multiple methods of cleaning the liners and tried different glass wool configurations to no avail.

Would you expect a method like this to be transferable between different inlets or are there some parameters (e.g. start temp) that are specific to the inlet?

A brief summary of the method;

6890/5973
inlet temp 280c constant
splitless with 50ml split purge after 1 min, 20ml/min gas saver after 5min
col flow 1.2 (constant pressure)
DB5.625 column with de-activated silica pre-column, quartz column connector
de-activated glass liner, tapered splitless end, de-activated glass wool in situ
oven start temp 60c (can't remember ramp - I will check tomorrow)
injection speed 'fast' (agilent default)
2ul injection
sample: 50% DCM extract/50%toluene PAHs/phenols at 2ng/ul

Before this I tried pulsed splitless, 1ul injection, and 90%DCM extract/10%toluene with no luck

any ideas?

First guess has to be a solvent effect - 1 ul of toluene condensing in the pre-column. Are the PAH peaks OK ?

How much wool is in the inlet ? You need the merest wisp, if any at all.

Can you post a chromatogram - instructions in a sticky at the top of the LC page.

Isn't the JAS a PTV inlet ?, if it is you could vent most of the solvent before going splitless to the column.

Peter

Also, watch out for the volume of the JAS inlet liner. I recall them as having less volume than the liners commonly used in the Agilent inlets.

The JAS UNIS liner is esentially a PTV inlet that takes a larger insert than the PTV inlet you purchase from Agilent. If you try to vent the solvent from this inlet, you need to have the glasswool present or some other way of providing surface for the injection to wet. Then you must evaporate your solvent well below the boiling point of the analytes (The number 70 degrees C difference in boiling points sticks in my mind.) For getting rid of DCM, you may be able to do this and retain the smaller phenols, with risk of discrimination. The boiling point of toluene is high enough that you may not be able to get rid of it with this technique.

You might try a split injection of a high level standard - even using a slow plunger speed. This will reduce expansion volume issues. See what the chromatography looks like.

I agree that split injection or smaller injection volume would help with solvent effects. Also, in my experience, phenolics are sensitive to injection liner conditions. Everything must be deactivated. You said that you tried different cleaning procedures. Maybe it is better to use new injection liners, or at least silylanize after a good acid soak. I can send you a procedure if you need one, or try google.

Thanks all, a few things for me to try on Monday.

The PAH peaks are fine, tailing a little but no worse than usual and a colleague in another lab has ran the same method and it works OK. I will try and get a chromatogram from him to compare.

I didn't try acid when cleaning the liners, but I have been muffling at 500c and silanising.

I did accidentally inject using a 50ul syringe instead of a 10ul so i could have possibly overloaded the column. I am trying a new column on Monday so I'll let you know how it goes.

i am intending to use the inlet in solvent vent mode for a pesticides method but i was hoping to run this splitless method until I have the pesticides method ready. Is this inlet simply unsuitable for this kind of method?

My understanding of this inlet is that it is supposed to give you the capabilities of the split/splitless inlet as well as PTV. I used one for a short time and did not have any problem with it in doing split and splitless work. And, I think that most of what I did was split - so I would have not run into liner size limitations. (It's been a couple of years ago.)

We really need to see a chromatogram.

Peter

Sorry guys, too busy to get a chrom today.

Turns out that the source of my method has been having problems too. I thought he was using it routinely but turns out that is not the case. We are both suspecting column but given we are both having same problem it could be method related.

new column fixed up the problem.

I think maybe because the column was uninstalled maybe moisture affected the column while the inlet was being installed - this made me think that the degradation of chromatography was due to the new inlet