Tetraethyllead non linear response

[LALman]

Colorado is about to require TEL measurements on suspected ground water projects. I got the 200ug/mL TEL standard 200ug/mL AccuStandard Cat# S-1263. I transfered it into 1mL Mininert vial just as I use for my 8260 standards.

I had just cleaned my source and was putting on an 8260 calibration. I got very good RSD's for my new calibration on the order of 5-7% RSD for all 79 regular compounds; except for TEL. It is distinctly non linear. I was able to fit a response factor curve (20, 40, 80, 120, 160 ppb) but any higher concentrations (240, 320, 400, 480 ppb) gave a sharply upward parabolic response. Running a 1 ppb and 0.2 ppb check standard of my whole cal curve gave me a nice 1.x and 0.2x ppb result.
My mass library hit for TEL shows the 208, 237 and 266 peaks. I ran it as SIM in SIM/SCAN mode using 237 for quant and 208 for check. 1,4-dichlorobenzene-d4 is the internal standard. TEL comes out on a DB-VRX column at 16.17 minutes just before the last 4 peaks. Not a strong peak.

Instrument is Agilent 5973inert/6890N with an Edwards 230 turbopump and a fastscan side board and log amplifier. Running 20m x 0.18mm ID x 1um coating DB-VRX column. Purge gas is LN2; purge temperature 70C; Archon autosampler; Tekmar 3000 P&T; desorbing at 250C for 1 minute; trap is vocarb 3000. Valve body and transfer line 150C, inlet 200C. Source 150C Quad 230C. Slow T ramp from 40C to 230C; 1,2,3-trichlorobenzene is the last peak out at 16.80 minutes.

After a quicktune the next day my 40ppb is coming back as 22ppb for both my CCV and MS aliquots in a sample run.

If you have had good luck with TEL; please chime in.

[DR]

Not experienced in this, but the reasoning for adding TEL to fuel all those years ago tells me that it will very likely muck up your source on a frequent basis...

TEL was added to fuels to coat valves and their seats and cushion the impact of valves on the unhardened seats and to help maintain that seal.

When TEL was outlawed, engine manufacturers started hardening valve seats and the business end of valves and incorporated tighter fit tolerances for them.

[LALman]

I've done some reading and here are some nuggets.
TEL boils at 89C and decomposes at 200C. Its solubility in water is 200ppb. It rapidly looses ethyl groups in soil bi- and mono- being the most likely remainder. Presence of gasoline or naple can stabilize TEL for longer.

I am desorbing at 250C; valve and transfer line at 150C; and inlet at 200C. So, I could be breaking off the first 2 ethyl groups in the trap. The mass mass library entry has 237, and 208 as the two largest peaks with 266 much lower. So bi- and mono-ethyllead may be the most stable in a purge and trap system. I can get a 9% RSD curve with 20, 40, 80, 120, 160 ppb using either 208 or 237 for quantitation and it goes bad above that concentration. So, that makes sense given the maximum solubility of 200ppb in water.

The GC-MS method I found suggested quantitating on 237 and 208 with 209 (PbH ?) and 266 as confirmation peaks.