Chromatography Forum

We are looking to buy a PLOT-Q type of column for MS use, mainly to identify traces of unknowns on a non-routine basis (e.g. refrigerants, small molecules). For 30m x 0.32mm there are film thicknesses available from 5 to 15 (or maybe more) microns. I would really appreciate a bit of advice on the effects of film thickness in PLOT columns.

ta!
John

If using a PLOT column with an MS, I'll probably suggest getting the thinner film thickness, since there is a higher bleed occurrence when using thicker films.

The technique to adhere particles into PLOT columns improved greatly, however, there is always a chance that few particles will dislodge, thus, it is suggested to use a particle trap (basically a guard column) in between your column and the detector.

Also, since you are going to use it mainly to identify traces, I assume you don't really need a great mass load capacity, another reason to avoid a thicker film PLOT column.

Gustavo
Supelco

Hi Gustavo, good advice, thanks

Another idea is to buy a union with an internal frit to avoid all particles from entering the MS.

A micropacked column also will allow a frit termination and will allow less chance of overloading the column (and broadening the main component peak) and an easy attachment of an union and FSOT tube into the detector.

best wishes,

Rod

We've got the standard Agilent turbo pump so column flow rate is limited to 2ml/min,a quick look at Restek says typically 3-5ml/min for micropacked columns so I don't think we could go that way. We would expected concentrations to be pretty small so I think the capacity of a capillary should be adequate.

micropacked columns fully packed (Restek has built-in voids at head and tail) work with flows from 1-20mL/min. Other vendors may offer frit termination, not wire bundles that Restek uses.

Capillary columns can certainly work. Retention column traps don't always work. Be aware.

Best wishes,

Rod

Some of the difficulty is that we don't have much idea what our analytes will be (this being the point of the method), but the highest resolution would give us the best chance of good (pure) peak spectra and therefore identification. I am still leaning towards a capillary for the greatest number of plates, would this be a fair assumption?

The big issue is how large a sample you inject. If you can inject a small (and narrow) enough sample you will get a higher number of plates.

Still connecting your analytical column using a frit containing union and a 0.10 or 0.15 mm ID FSOT tube into your detector would be a good idea to prevent any particles entering your detector. If you might have VERY REACTIVE analytes then don't bother as the metal of the frit COULD be an issue.

I would use a capillary column FIRST as I assume this would be a more flexible means of sample injection for your hardware at this time.

Good luck in your work,

Rod

The sample will come from a P&T, carrier gas is routed via this, transfer line connected to column head directly. The column tail goes to a Deans splitter which maintains 4psi, and from there to FID and MS. We have the option of using a gas sampling valve instead of the TD but odds are the analytes will be too dilute for direct injection. Analytes will most like be things like solvents but could be odour compounds.

Restek say their Q-bond columns are the latest thing and don't shed so many particles, or there is Agilent PoraBond Q, similar claims, I wonder how much different they really are though?

Please note that neither company states that their columns will NOT shed particles.

A word to the wise.....................

best wishes,

Rod