EZ No-Vent GC Column-Mass Spectrometer Connector - any good?

Discussions about GC-MS, LC-MS, LC-FTIR, and other "coupled" analytical techniques.

15 posts Page 1 of 1
Hi,
I help run an analytical lab at a University for teaching and research users. We have two GCMS's:
    Varian CP3800/Saturn 2200 (GCMS/MS)
      Agilent 6890N/5973 inert MSD (GCMS)

      Due to these instruments being used by both undergraduate students and postgrad researchers, they is a requirement to frequently change the columns in these instruments.

      This results in a lot of downtime (it can take a day to change a column and get the instrument back up and running) and I am aware that the number of times we vent and pump down the instruments places strain on their turbopumps (we've recently had to replace the Varian's).

      I have read about "EZ No Vent" GCMS connectors that claim you can change the column without having to vent the system. These seem like the answer because this would prevent the strain to the turbopump and reduce the time taken to change the columns.

      My question is: has anyone used these types of connectors and do they work? Are they as good as they sound or are their negatives I should be considering?

      Please help. I am new to GCMS support and would value experienced insight.

      Many thanks,
      Gemma, Lab Technician
      I don't use the EZ No-Vent connector, but it sounds the cheapest and easiest solution for your problem. The instructions can be found here:

      http://www.restek.com/pdfs/203-03-023.pdf

      What I do use and can be used for the same purpose is a purged union:

      http://www.agilent.com/cs/library/broch ... ochure.pdf

      Here, you connect your analytical column with a piece of uncoated column that is inserted in your MS. The connection receives a flow of carrier gas. Besides being able to change analytical columns without venting/pumping the MS, the big advantage is being able to perform backflush. Worth looking into if you run dirty samples, for example pesticides in food. Works really nice.
      The No-Vent just uses a piece of 0.1 ID transfer line that attaches to one side of the fitting and your column attaches to the other. The smaller column provides enough restriction that the flow into the instrument due to vacuum is small enough to not trip the pump into vent mode. They work ok until you get a piece of ferrule or other contaminate into the small transfer line, then you have to vent and change the transfer line. Depending on how careful the ones changing the columns are will depend on how long it will work.

      What I do if I am wanting a quick change is put the turbo pump into vent mode then remove the old column from the inlet but leave it in the mass spec and plug the inlet end with a septa. Next install the new column, allow it to purge with carrier flow a few minutes, prep the mass spec end for installation by putting on a nut and ferrule and marking it at the outside of the nut for the proper installation depth. Next quickly remove the old column, and slide the new column in, adjust the depth to the mark and tighten the nut. You will get a slight gurgle at the rough pump but never lose rough vacuum on the system. Now you just have to go to pump down mode, the turbo will spin up and the heaters will come on and within a few hours you are ready to go with very little if any air and water in the system.

      I have seen it done with the turbo still running, but I think it puts too much strain on it myself and if you aren't really really fast it will still trip over into vent mode due to loss of speed. If you go into vent mode the source will cool to 100c which is good enough and not be much lower than that once you are ready to pump down again which saves time on coming back to a ready state. You also are not exposing the multiplier to atmospheric pressure each time which helps extend the live on it also, though the new ceramic types are not as affected by that as the old Galileo ones were.

      I have only done this on the Agilents, not sure how easy it would be on the Saturn. With practice you will be able to pull the old one out and put the new one in within about 5 seconds and barely hear the gurgle of the rough pump. If you have an assistant who can hold a septa against the interface, you can take longer to make the swap with less air getting in, but I rarely ever have an assistant handy )
      The past is there to guide us into the future, not to dwell in.
      James_Ball wrote:
      What I do if I am wanting a quick change is put the turbo pump into vent mode then remove the old column from the inlet but leave it in the mass spec and plug the inlet end with a septa. Next install the new column, allow it to purge with carrier flow a few minutes, prep the mass spec end for installation by putting on a nut and ferrule and marking it at the outside of the nut for the proper installation depth. Next quickly remove the old column, and slide the new column in, adjust the depth to the mark and tighten the nut.


      This sounds like a bad habit to me :P
      I use the No-Vent for a couple of years now. I had not any problem till now. Our instrument is equipped with an oil diffusion pump, so I do not know the impact of a turbo pump.
      The only disadvantage I see is that you have to add 82 m of virtual length to your column (0.25 mm ID), which increases the column head pressure well over 200 kPa with helium.
      Other than that, it takes about an hour for the MSD to be ready for use (low air and water peaks in the mass spectrum)
      Regards,
      Gilbert Staepels

      Ideas mentioned in this note represent my own and not necesseraly those of the company I work for.
      Thanks everyone for your responses. We have decided to go ahead and purchase one for our Agilent GCMS and try it out.
      gstaepels has a point; you may find that existing methods can't cope with the extra pressure necessary to maintain the desired flow through the column.
      lmh wrote:
      gstaepels has a point; you may find that existing methods can't cope with the extra pressure necessary to maintain the desired flow through the column.


      I ran into that when I was working with connecting two columns together just before the MS inlet. When you use a very narrow transfer line, the end of the column no longer see hard vacuum and you have to compensate by telling the instrument the column is longer than normal or has a smaller ID. When I switched from a 0.1ID transfer line to a 0.53 transfer line, then the calibration was accurate because the transfer line was large enough that the end of the column was seeing full vacuum.
      The past is there to guide us into the future, not to dwell in.
      Rndirk wrote:
      James_Ball wrote:
      What I do if I am wanting a quick change is put the turbo pump into vent mode then remove the old column from the inlet but leave it in the mass spec and plug the inlet end with a septa. Next install the new column, allow it to purge with carrier flow a few minutes, prep the mass spec end for installation by putting on a nut and ferrule and marking it at the outside of the nut for the proper installation depth. Next quickly remove the old column, and slide the new column in, adjust the depth to the mark and tighten the nut.


      This sounds like a bad habit to me :P


      Very bad habit :) I much prefer to be able to open the analyzer and verify that the column is inserted the correct amount past the end of the interface, those measuring tools can be off a couple mm sometimes. Of course it seems more often than not we have rush samples sitting waiting any time we need to change a column. Murphy needs to be disbarred :lol:
      The past is there to guide us into the future, not to dwell in.
      I'm looking at using one of these or the Agilent union on an instrument that would need to routinely swap between columns (probably twice a month on average.) Anyone have any updated input on performance, longevity, other issues, etc? Does the PCT work with a 5973?
      My service guy told me this would cause flow problems and I worry about room air getting at my hot source. My 5973inert/6890 setup has a standard turbo. I have the roughing pump on standalone circuit. So I vent the 5973 with rough pump still going. Let it cool down, shut off rough pump. swap column. Start on roughing pump. Then do rest of pump down before heating source over 100C. System pumps down plenty quick. Same as swapping in a new filament.

      I suppose an advantage could be having an inert transfer line that never gets swapped and therefore never outgasses into MS.
      andrew ryder wrote:
      I'm looking at using one of these or the Agilent union on an instrument that would need to routinely swap between columns (probably twice a month on average.) Anyone have any updated input on performance, longevity, other issues, etc? Does the PCT work with a 5973?


      If you need to swap between different phase columns often you may want to add a second injection port and try the dual column setup I listed above. Of course they columns have to have similar max temperatures, if not you limit max oven temp to that of the lowest max column temp.

      I have one 5973 setup now to run EPA530 and EPA541, one using a 1701 column and one using a wax column and I have been running it for 9 months without needing to vent, which is great for uptime.
      The past is there to guide us into the future, not to dwell in.
      James_Ball wrote:
      If you need to swap between different phase columns often you may want to add a second injection port and try the dual column setup I listed above. Of course they columns have to have similar max temperatures, if not you limit max oven temp to that of the lowest max column temp.

      I have one 5973 setup now to run EPA530 and EPA541, one using a 1701 column and one using a wax column and I have been running it for 9 months without needing to vent, which is great for uptime.


      Thanks James. Are you referring to the technique above where you quickly swap columns while leaving the rough pump running? Our system does not use a turbo pump.
      andrew ryder wrote:
      James_Ball wrote:
      If you need to swap between different phase columns often you may want to add a second injection port and try the dual column setup I listed above. Of course they columns have to have similar max temperatures, if not you limit max oven temp to that of the lowest max column temp.

      I have one 5973 setup now to run EPA530 and EPA541, one using a 1701 column and one using a wax column and I have been running it for 9 months without needing to vent, which is great for uptime.


      Thanks James. Are you referring to the technique above where you quickly swap columns while leaving the rough pump running? Our system does not use a turbo pump.


      Sorry I was thinking of a different post. I have an instrument set up with a front and rear injection port to which I have two different columns attached. At the end I have the two columns going into one of the Restek MXT metal Y connectors. I then use a portion of 0.53 MXT steel transfer line going from the Y connector into the MS. You have to use the large diameter transfer line so that the ends of the analytical columns (which should be 0.18ID, but 0.25ID will work) will be terminating at a vacuum so that the GC can calculate the correct head pressure for the flow in the column.

      When using the front column set the flow to 1-1.2ml/min and the rear column to 0.3-0.4ml/min or vice versa when using the rear column for analysis. With this you can actually set up two different methods for two different types of samples to run overnight, just switching from the front column method to the rear column method during the sequence after the first set of samples is finished. With this one instrument could run two batches of different samples overnight instead of running one set today, swapping columns and waiting for vacuum and temperatures to stabilize tomorrow and running the second batch of samples the third day. For the cost of a second inlet, you get the productivity of two instruments, or at least 1.5 instruments since you can't run the two methods at the same time.
      The past is there to guide us into the future, not to dwell in.
      I use the Agilent quicswap system which is basically a purged union that sits on the transferline. It is fed Helium at 4psig from an auxilary EPC on the 6890GC and the column connects to it using a typcal Agilent CFT metal ferrule. On the other side is a 17cm .100mm deactivated capillary that goes through the transfer line and provides flow resistance. When you undo a column the helium being purges spews out the column connection ~30 ml/min and no significant amounts of air gets into the MS. The main weakness is the connection to the transferline is touch with a silltite ferrule comes preswaged on the capillary and is sandwitched between the quickswap and transferline end. It can be tricky to get a seal and it is a pain to take off anytime you have to separate the MS from the GC to do maintenance.
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