Chromatography Forum

I need a suggestion for a proper trap to use for TetraEthylLead [TEL] if one exists. I can get 739,000 counts for 160 ppb counts by direct injection: I get a nice peak with masses clustered at 207, 237, 266, 295, and a tiny molecular peak at 324. For reference, 70 ppb fluorobenzene is 4 million.

Instrument is an old HP 5971/5890 II with diffusion pump and an upgraded 5972 top board and mainboard. Running 20m x 0.18mm ID x 1um coating DB-VRX column. Purge gas is LN2; purge temperature 70C; Archon autosampler; Tekmar 3001 P&T; desorbing at 150C for 1 minute; trap is vocarb 3000. Valve body and transfer line 150C, inlet 150C. Source ~170C. Slow T ramp from 40C to 230C; TEL comes out at 16.8 minutes.

If I do this via the P&T I get a much smaller peak of 268,000 counts for the same 4uL of 200 ppm TEL standard. For reference 70 ppb fluorobenzene is 5 million.

Its more about purge efficiency than the trap, but your desorb temp at 150C is way too low. 250C is the recommended desorb temp for that trap.

Our desorb temperature is normally 250C and the inlet is normally 200C. We lowered the temperature on this older instrument to experiment with conditions.

Because on our more sensitive 5973inert/6890 (Fluorobenzene 15 million counts) we were getting 2.8million counts from the same 4uL of 200ppm TEL stock; which was 160 ppb for a 5 mL P&T vial.

We got something linear for 20, 40, 80, 120, 160 ppb but very non linear for 240, 320, 400, and 480 ppb. Then when we ran standards for that lower range they were all over the place.

So, do you think if we R&R the inlet, the Vocarb 3000 is going to be OK for this? I should add we are purging with gassified LN2 from a dewar rather than helium. Would helium or argon be better for TEL consistancy?