Designing the ideal standby method

Hello all

 

I'm looking at designing some standby methods for my 4 GC-FIDs and 3 GC-MSs as they are often sitting idle for 3/4 days a week and are happily consuming helium, hydrogen and generally sucking money away basically for no reason. Turning them off/on is not an option as we often need some of them fairly urgently, so I thought a 'Standby' method would be the best way to conserve!

 

I just want some advice on the key things to be looking at regulating. From scrawling this and other forums I've pieced together the following information so if anybody spots any glaring holes, please let me know

 

Oven temperature: Low (30-50)

Column: Carrier gases set to a minimum flow (~0.5ml?) to protect column and/or MS (we are an oils lab so use non-polar columns)

FID: Keep at around 100 to prevent moisture forming on jet. Turn off all gases except for carrier gas

MS: Keep at temperature to ensure no build up of moisture/solvent anything on source etc. Same with aux line?

 

My main point of concern is the inlet. We have split and splitless injectors - how much flow do we need to keep going for the split flow? Any? Low? I've seen some people say to set the method to splitless and put a low flow on it (1-2ml/min). Currently it's on Gas Saver running 20ml/min which I feel is fairly high compared to the remainder of the system.

 

Any advice on this will be appreciated!

Parents
  • Hi ryanedwardson,

    The idea to create a standby method is a good one. Many instrument users do this successfully, but many others create methods that shorten column life and end up costing more money in the long run. The idea of a standby method is to keep the system healthy and able to perform at a moments notice. All points that you outlined. I have been a service rep since the late 1980's and some of what I will suggest here will cause debate for those that are able to create methods that are below factory spec and seemingly have no issues.

    Taking your points:

    Oven temperature: Low (30-50) ( My suggestion, stay at the main method starting temperature)

     

    Column: Carrier gases set to a minimum flow (~0.5ml?) to protect column and/or MS (we are an oils lab so use non-polar columns) (Reducing column flow in some cases with reduced oven temperature can leave the column with not enough flow and head pressure to keep a column healthy and prevent air infiltration through the split vent. You are only saving 0.5ml/min typically here anyway so its not worth it)

     

    FID: Keep at around 100 to prevent moisture forming on jet. Turn off all gases except for carrier gas (Gases off, but keep the temperature up to eliminate any siloxane build up from the column. 150c or higher. Higher temperature costs nothing, moisture should not be an issue anyway with proper gas purity and filters)

    MS: Keep at temperature to ensure no build up of moisture/solvent anything on source etc. Same with aux line?( Yes)

     

    The Inlet should maintain proper total flow to maintain its operation, this is why Agilent/HP came up with the gas saver feature. The older instruments such as the 5890 just had a total flow knob and usually it wasn't adjusted for times when the instrument was idle and used more gas. Gas saver also kicks in at a defined time , such as 2 minutes, as high flow is really only needed at injection. This next statement may cause the most discussion. Leave the total inlet flow at 20ml/min in gas saver, you could try and reduce it to something like 15ml/min (below factory specs) , but keep in mind we want to maintain head pressure and avoid any air entering the inlet through the split vent which is detrimental to the column. In short, you have a modern instrument  with saving features already there, Gas saver, EPC detector flow for FID gases can be off with the simple load of a standby method. I hope this helps.

     

     

     

    Regards

    James

  • Thanks very much James - great advice.

     

    I knew I was on the right track, but like you said there's a line there between savings and causing damage to your instrument which ends up costing you more!

     

    I'll keep the inlet going at 20ml/min, I feel like that's where most of the problems can start.

     

    For the FID, we use Hydrogen, Comp Air and Helium. Helium is also our column carrier gas - can I switch off the 'extra' helium supply and just leave the carrier gas running to it. Is that sufficient? Or am I better keeping a supply going but reduce the amount - currently they run about 40ml/min which is quite high in my view!

     

    Thanks again

    Ryan

Reply
  • Thanks very much James - great advice.

     

    I knew I was on the right track, but like you said there's a line there between savings and causing damage to your instrument which ends up costing you more!

     

    I'll keep the inlet going at 20ml/min, I feel like that's where most of the problems can start.

     

    For the FID, we use Hydrogen, Comp Air and Helium. Helium is also our column carrier gas - can I switch off the 'extra' helium supply and just leave the carrier gas running to it. Is that sufficient? Or am I better keeping a supply going but reduce the amount - currently they run about 40ml/min which is quite high in my view!

     

    Thanks again

    Ryan

Children
Was this helpful?