questions about switching to packed column

[ljhainsw]

Hi All, I have a new Agilent 7820a and I am working on ethylene analysis in air. I'm getting ok results with my capillary column with FID, but I'd like to try to improve the signal by switching to a Porapak Q packed column. (I read about this in someone's earlier post.) My question is, do I need any special adapter kit to install a packed column? Will the split/splitless injector work for 1mL injections? Also, on the Supelco page they offered two choices - Agilent configuration "A" and configuration "C". How do I know which one I have?
Thanks so much - any information will be helpful!

[chromatographer1]

Many use a valve to make injections using packed columns with an Agilent GC.

How will you be injecting?

You need to read and understand the manual using packed columns.

Time to do your homework.

best wishes,

Rod

[larkl]

1 ml should work with the SSL injector. You can always increase the split if you need to. I'd say 0.5 ml injection would be more common, but some may disagree. I'm not sure I'd go to all the work to switch to a packed column. You can't get what you need with the capillary. We do these sorts of tests routinely using capillary columns. I'd add a 6 port Valco (VICI) valve to the carrier inlet upstream of the inlet to inject the sample.

[ljhainsw]

Thanks for your replies. I checked the users manual and it describes the installation of a packed metal column with a purged packed injector, but not with a split/splitless. So it seems that I would need a new injector, as well as an adaptor kit for the FID. I teach at a very small college, so I need to keep costs low and I also need to be able to use the instrument for undergrad. lab experiments. I've never used a Valco valve before, I'll have to look into that a bit more. Thanks again!

[chromatographer1]

The configuration of front or back injector accommodating the detector choice is the reason for configuration A or C with a glass packed column.

You might consider a micropacked metal column using the split - splitless injector. Cheapest choice to get the job done.

micropacked columns can tolerate 20cc/min to 0.2cc/min carrier flow rate, if you use capillary tubing and unions to attach the column to the injector and detector.

best wishes,

Rod

[larkl]

The valco vale is going to set you back quite a bit. http://www.vici.com/support/app/app11j.php Maybe $900 if air actuated, but then you need the actuator for the air. Electrically switched is maybe $1200.

You can do a syringe injection with a gas tight syringe. It won't be the most precise, but it's inexpensive and may be Ok for student work.

[aldehyde]

I would say that you could find a spare purged packed inlet for fairly cheap, but unfortunately the 7820 has a different design for it's pressure controller and the 7820 hasn't been out long enough to develop a large supply of cheap spare parts.

I don't know for sure (pricing for schools etc) but I think the purged packed inlet + epc would cost more than the valve the others are referencing. The adapter you would need for the FID is cheap--*as long as you can use the adapter*. Make sure to look at the actual place where you install your column. Is it just a straight metal tube that is threaded on the inside (capillary dedicated FID base) or is it an adapter screwed on with a 1/4 inch swagelok nut?

This page shows what I'm talking about: http://www.chem.agilent.com/en-US/Suppo ... olumn.aspx

if you have the capillary dedicated FID base you're not going to be able to install a packed column.

[AICMM]

ljhainsw,

A manual Valco valve will do what you want for about $600 which is about as cheap as it comes in this business. Yes, you can mount any packed column to the FID if you use a capillary transfer line (ad Rod notes; piece of cake.) No, you cannot easily mount a full on packed column to your inlet because it is EPC controlled (this would have been easy with a 5890 and manual pneumatics but that is not the case here) and the EPC will choke on the modifications needed. Your will spend several thousand on the appropriate inlet and EPC (and make sure your 7820 can support both a packed and splitless/split.

The bigger question, in my mind, is why you want to go packed? To shoot more? You might consider plumbing a valve into your split inlet. This will allow you to run with a small split ratio and shoot a fairly large volume of sample onto your PLOT column which is a pretty elegant solution way to do things (having seen it done.) It also allows you to maintain splitless/split capability for other classes. You could also consider a more sensitive detector to get you down to the levels you need although I suspect the inject more solution will get you where you need to be.

Best regards,

AICMM

[AICMM]

ljhainsw,

I went looking yesterday and it appears that the 7820 is manual pneumatics? Is that the case?

Best regards,

AICMM

[Johnny Rod]

Ours is fully EPC. What level of ethylene are you looking for and what capillary column are you using at the moment?