AJS ESI Sheath gas flow in standby mode

Question

Hi there, 
 I have noticed that when we start pumping down our 6460 QQQ, the system originally remains in standby mode where sheath gas flow is 0L/min and sheath gas temp is 29oC , while drying gas flow and temperature are set to 3L/min and 300 oC, respectively (see screenshot below). 
 After turning the system to "Run mode" for the first time and then back to standby, sheath gas flow and temperature are then set to 3 L/min and 125 oC (by default) , respectively. So, it seems that the two standby conditions for sheath gas are equivalent for Agilent. 
 Is there any way to set sheath gas flow to 0 L/min and sheath gas temp to 29oC as default settings for Standby mode? Besides saving some N2 gas, the noise from N2 generator (PEAKS with internal compressors!) will be reduced as it will switch on the noisy compressors less frequently. Any suggestions?

m4esti · Accepted Answer

Hi manman, 
 No there is not. 
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Agilent · Answer

Hi Manman, I think I can answer your question. It is because when the LC/MS QQQ is initially pumping down to high vacuum, there is initially very high power loading placed on the 2 high vacuum Turbomolecular pumps, particularly the 1st Turbopump which is under high very power/ high load & higher stress while evacuating the high volume of air inside the LC/MS QQQ vacuum chamber. To help avoid getting potentially hydrocarbon contaminated laboratory air from being drawn inside the Mass spec vacuum chamber while the vacuum pumps are running (which would give you a higher chemical background in your LCMS spectra), there is a standby setting for the Drygas to apply a minimal amount of 3 L/min as well as some Drygas heating to help also reduce the viscosity of this Drygas so that instead of Laboratory air being pulled into the Mass Spec through the ion capillary, a small amount of clean N2 gas from the Drygas & Nebulizer is pulled in instead. 
 If the Sheath Gas flow from an AJS ion source was also turned on, it would place even greater demands on the 2 turbo pumps to pump down the LC/MS down & the whole LCMS system would take a lot longer to pumpdown to sufficient high vacuum & it would probably not be very good for the overall robustness & expected lifetime of the turbo pumps, so this will be reason why Sheath gas flow & temperature (due to metal surface oxidation at higher temperatures when there is no flow) are not turned on during pumpdown. 
 I don't think it is possible to change any of these factory standby Ion source settings. 
 
 Kind regards, 
 John

AJS ESI Sheath gas flow in standby mode

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