Separation problem with 5890 GC

[jarod]

Dear all

I have 6 components to separate: acetone, ethyl-acetate, ethanol, methyl-ethyl ketone, toluene,styrene. Which column is the best choice? ZB-1 or ZB-WAX? These components are in CS2 solvent.
I have tried ZB-1 and ethyl-acetate had 3 peaks instead of one. And the same happened to methyl-ethyl ketone. Is it possible that my standards were contaminated? In addition MEK peaks were interwoven with solvent peak(CS2).
Condition: inlet: 220°C
detector(FID): 280°C
ZB-1 column
carrier gas: nitrogen
Temp. prg: 40°C 8 min, 5°C/min 60°C 18 min.
Thank you for your help in advance!

[AICMM]

At 40C initial using CS2 you will not get any re-focus from the solvent. That could explain the multiple peaks for early eluting components.

What film thickness and diameter are you using? Yes, you might want to try a more polar phase than a -1 but I would say wax is the opposite extreme and still might not solve any problems if the phase is not thick enough.

Best regards.

[jarod]

Thank you for your quick reply!
Sorry, I don't know the exact measure. I send it tomorrow. I will try a more polar phase as you suggested.
Thanks!

[Peter Apps]

Sounds like a solvent effect to me. What volume are you injecting, and are you running split or splitless ? Is this part of a method that uses CS2 to elute analytes from an adsorbent ?

Peter

[jarod]

Hi Peter
Yes, these components i measure are in the air. Adsorb on activate carbon and elute in CS2. I'm new in this measurement.
I inject 1ul and I don't know it is a splitless or split injection, I'm only trying to reproduce my former colleague's method. Can you explain what is a solvent effect? How can I set a split method if I only have column head pressure gauge on the instrument?
Thank you in advance!

[Peter Apps]

Hi Jarod

Please post full details of your method and the hardware that you are using, then we can start to torubleshoot based on known facts.

Peter

[MikeD]

Jarod,

Don't forget to add the details of your air sampling method - air volumes, expected concentrations, amount of carbon etc. It would help to decide what split you need.

[jarod]

I only know the following details: Sample collected -ca. 50 litres air- on activate carbon(amount?), desorbing with 1ml CS2. Inject 1ul in the GC.
GC: HP 5890 series II, FID detector.
Column: RTX-1 25mx0.32mmx0.5um df
Program: I have mentioned my first post.
I hope it would help in troubleshooting! Thank you!

[AICMM]

jarod,

From your earlier post it sort of sounds like you have a packed column injector? You have only one gauge but how many flow control knobs, one, two or three? Furthermore, you have a short and thin film column which will be difficult to make work for the list of target compounds you have. What are the dimensions of the wax you have available?

Best regards.

[jarod]

Dear AICMM
Sorry for my late reply, I'm so busy! I have straight 2mm ID liner packed with glass wool. My former colleague used it for this separation. The dimensions of ZB-Wax column are: 30m x 0.32mm x 0.5 um df.
I have two knobs: total flow and a septun purge flow.
Thank you for your help!