P&T problems
Posted: Thu Mar 27, 2008 6:28 pm
We are having a problem with EPA method 524 where our fluorobenzene (IS) response drops over time to > 50% of the average calibration response. FLuorobenzene elutes at about 12 min. on our system, BFB at 18 min., and 1,2-DCB d4 at 20 min.
We have a Tekmar Velocity that is about 5 years old. We use a VOCARB 3000 trap with the following conditions:
11 min purge @ 40 cc/min
3 min dry purge @ 90 cc/mi @ 30 degrees C
desorb preheat 190
desorb temp 220 for 4 min
bake @ 260 for 8 min
We started using this system on an Agilent 5890/5970 and did not notice any problems. We were using a 75M 624 column @ about 10 cc/min with a jet separator.
We noticed our IS dropping shortly after switching to a 6890/5973 system. We use a 624 column 60M X 0.25 X 1.4 @ 1.9 cc/min. We use a 2mm inlet liner and split at 30:1.
We had used a tweaked autotune to meet the BFB requirement. Our new system sets the base peak durring autotune to 219 which renders our tweaks unusable. We now use the "canned" BFB tune which dynamicaly ramps the entrance lens offset.
I feel our problem is due to the water in the source affecting the ionization. This water builds up over time due to the pumping rate of the system ( our system is CI capable so has the largest pumps). The response jumps back after the sstem sits idle for a time.
Has anyone tried the Tekmar " dry trap"? We use a blank trap in this position. Would a higher split ratio or 4 mm liner help eliminate water?
This is an EPA method so we have to desorb for 4 min.!!!!
Thanks in advance
We have a Tekmar Velocity that is about 5 years old. We use a VOCARB 3000 trap with the following conditions:
11 min purge @ 40 cc/min
3 min dry purge @ 90 cc/mi @ 30 degrees C
desorb preheat 190
desorb temp 220 for 4 min
bake @ 260 for 8 min
We started using this system on an Agilent 5890/5970 and did not notice any problems. We were using a 75M 624 column @ about 10 cc/min with a jet separator.
We noticed our IS dropping shortly after switching to a 6890/5973 system. We use a 624 column 60M X 0.25 X 1.4 @ 1.9 cc/min. We use a 2mm inlet liner and split at 30:1.
We had used a tweaked autotune to meet the BFB requirement. Our new system sets the base peak durring autotune to 219 which renders our tweaks unusable. We now use the "canned" BFB tune which dynamicaly ramps the entrance lens offset.
I feel our problem is due to the water in the source affecting the ionization. This water builds up over time due to the pumping rate of the system ( our system is CI capable so has the largest pumps). The response jumps back after the sstem sits idle for a time.
Has anyone tried the Tekmar " dry trap"? We use a blank trap in this position. Would a higher split ratio or 4 mm liner help eliminate water?
This is an EPA method so we have to desorb for 4 min.!!!!
Thanks in advance