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- Posts: 10
- Joined: Mon Aug 13, 2007 2:56 pm
Hope someone can assist with this. We have a HP5890 Series II GC that for 14 years was connected to a P&T system where the sample was split via a jet separator before going into a HP5972 MS. Our application is Environmental- 8260 (rev c) analysis. We are in the process of converting it to connect from the P&T to the 5890 through the injection port, eliminating the jet altogether. We've almost got all the bugs ironed out, except I think I "may" have a leak in the injection port. We have the Helium gas line feeding a Solatek 72, 3100 P&T and the 5890 GC at a feed pressure of >100psi. My split vent flow out of the port in front of the GC is 120ml/ min (bear with me, there.That's part of the issue). Septum purge flow out of the vent is 1.6 ml/min. Purge flow out of the P&T vent is 35 ml/min, and flow into the Agilent DB624 25m .20mm ID column is .8 ml/min. The purge valve is "off" initially, then is turned on right at GC start and then turned off again at 2 minutes (to save Helium between runs) The transfer line from the P&T is now connected to the injection port via a 1/16" swagelok union. We would ideally like to achieve a split flow of about 30-40ml/min and a flow into the column of 1 ml/min, but if we adjust the total flow knob in front of the GC to reflect this desired split, the pressure alarm will start to activate approximately 2/3rds of the way into the run and you can see the total flow drop off once the temperature increases, as it looks like the actual EPC pressure in the injection port is struggling to keep up with the programmed setpoint for the method as the temperature increases, usually when the temp gets up to >100 degrees. I keep our flowmeter attached to the split vent line to monitor and from a starting point of 120ml/min, the flow gradually drops off until the end of the 17 minute run at which point flow is restored (almost immediately, I might add). By the end of the run, the flow out of the vent is at 20ml/min, which is why the total flow is set that high, as anything lower will set off the alarm as the EPC pressure readings can't keep up based on the flow reaching zero. I am getting peaks, but they are suppressed, and not nearly at the abundance of where they should be.
Since the inner diameter of the P&T transfer line is smaller compared to the tubing of the injector, we had to use a vespel ferrule instead of a stainless one on the one swagelok fitting. The other end of the union (at the injector) has the regular stainless ferrule, so I don't know if that ferrule is an issue, I'm not quite sure what other type ferrule can be used for that transfer line connection.
Anyway, does the dropoff in flow as the temp increases ring a bell with anyone as to where this leak (if it is a leak) might be originating from. The column nut, septum, swagelok union, liner and column are all new. The gold seal is not. Since the unit has not been run this way in the 14 years we've had it, is a valve possibly the culprit? Any thoughts would be much appreciated.
Since the inner diameter of the P&T transfer line is smaller compared to the tubing of the injector, we had to use a vespel ferrule instead of a stainless one on the one swagelok fitting. The other end of the union (at the injector) has the regular stainless ferrule, so I don't know if that ferrule is an issue, I'm not quite sure what other type ferrule can be used for that transfer line connection.
Anyway, does the dropoff in flow as the temp increases ring a bell with anyone as to where this leak (if it is a leak) might be originating from. The column nut, septum, swagelok union, liner and column are all new. The gold seal is not. Since the unit has not been run this way in the 14 years we've had it, is a valve possibly the culprit? Any thoughts would be much appreciated.
