GCMS Mystery air leak or something else?
Posted: Fri Feb 28, 2025 11:19 am
Posted this over in the hyphenated techniques forum as well....
We have a Trace 1300/ISQ GCMS from Thermo Scientific. A few weeks ago the DC power supply to the GC failed overnight and somehow that allowed the remaining helium in the cylinder (at 600 psi) to leak out totally emptying the tank. Thermo Scientific was onsite the next day to replace the power supply while I changed to a new tank and new Restek triple gas filter cartridge as the old one was saturated with air. If I'm not mistaken, the Restek filters are shipped filled with helium. I also changed the inlet septum and liner.
Every connection including the inlet was then leak checked with an electronic leak detector by the Thermo Scientific engineer as well as myself with my own detector. No leaks were found. The engineer tuned the instrument with no issues. We let the helium flow through the system overnight. However, the next morning the nitrogen was about 10X normal swamping both the water and oxygen peaks which is not how it normally appears after flowing overnight. I suspected a bad tank and changed to a new one from a different lot and let it flow through the system over the weekend. On Monday morning the nitrogen in the air water check was again at about 10X normal with the ratio of N2 to oxygen being about 22:1.
Every connection was leak checked again and the transfer line nut sprayed with electronics dust-off. No leaks were found. If it’s an air leak, it would have to be before the gas filter, but the filter is after two weeks still pristine – no color change in the oxygen filtration portion of the filter.
Our gas supplier provided COAs for the two lots and nitrogen was measured at < 8 ppm for both lots and also noted that they had received no complaints about high nitrogen in either of these lots. So it doesn’t seem to be the tank.
I am at a loss to figure out what is going on, but something tells me it is related to the tank running completely dry. Anyone have any suggestions on what it might be?
Michael
We have a Trace 1300/ISQ GCMS from Thermo Scientific. A few weeks ago the DC power supply to the GC failed overnight and somehow that allowed the remaining helium in the cylinder (at 600 psi) to leak out totally emptying the tank. Thermo Scientific was onsite the next day to replace the power supply while I changed to a new tank and new Restek triple gas filter cartridge as the old one was saturated with air. If I'm not mistaken, the Restek filters are shipped filled with helium. I also changed the inlet septum and liner.
Every connection including the inlet was then leak checked with an electronic leak detector by the Thermo Scientific engineer as well as myself with my own detector. No leaks were found. The engineer tuned the instrument with no issues. We let the helium flow through the system overnight. However, the next morning the nitrogen was about 10X normal swamping both the water and oxygen peaks which is not how it normally appears after flowing overnight. I suspected a bad tank and changed to a new one from a different lot and let it flow through the system over the weekend. On Monday morning the nitrogen in the air water check was again at about 10X normal with the ratio of N2 to oxygen being about 22:1.
Every connection was leak checked again and the transfer line nut sprayed with electronics dust-off. No leaks were found. If it’s an air leak, it would have to be before the gas filter, but the filter is after two weeks still pristine – no color change in the oxygen filtration portion of the filter.
Our gas supplier provided COAs for the two lots and nitrogen was measured at < 8 ppm for both lots and also noted that they had received no complaints about high nitrogen in either of these lots. So it doesn’t seem to be the tank.
I am at a loss to figure out what is going on, but something tells me it is related to the tank running completely dry. Anyone have any suggestions on what it might be?
Michael