LALman wrote:
The vacuum has improved and the system is tuning better since I first pumped down. This system always pumps down fast and gets operational fairly quickly but it takes at least a couple of weeks before it really gets a good vacuum. I assume this is absorbed water. I tried to mitigate by immediately closing the chamber up after removing the source and leaving it on backing pump vacuum until I was ready to reinstall the cleaned source.
I've also ordered new o-rings for the EPC interface block. Its amazingly sensitive to leaking if you poke at it while monitoring the nitrogen peak.
Question, my 8260 run is 16.6 minutes for all the compounds to elute. But I run it out to 19.5 minutes to run out late heavies like DRO and because P&T unit is so slow. I wonder if I am straining my standard turbo pump by setting a high flow for part of each run.
I desorb at 1 mL/min but at 2.00 min I ramp to 1.3 mL/min, then at 9.3 min I ramp to 1.5mL/min and finally at 19 min ramp back to 1.0 mL/min. This along with my temp program lets me almost completely separate BFB from o-xylene sufficient that I can pass BFB in my CCV standard.
I do purge and trap volatiles using a 20m 0.18ID 1um film column, either the Rxi-624SilMS or the older Rtx-502.2 columns from Restek. At 0.8 to 1.0ml/minute I can do a run out through 1,2,3-Trichlorobenzene/Naphthalene in 16-20 minutes with no problem separating BFB from other analytes.
Even 1.3ml/min though should be ok with a 5973 turbo or diffusion pump. One thing we do is use E2M2 rough pumps and I also use molecular seive traps just before the roughing pump to keep moisture out of the oil. These used to come standard on the 5971/5970s and I have just moved them across platforms as we upgraded.