BHT in Water Matrix

[mbdixon]

Hi I have been trying to calibrate my HP6890GC with FID detector to detect BHT (Butylated Hydroxy Toluene) in a water matrix. I have standards of 3 to 60 ppm, with myristic acid (I had it in the fridge) as IS. The BHT and IS were dissoled in methanol in intermediate standards.

Inlet Conditions : Splitless, Temp 250°C, Purge Time 1.00, purge Flow 50.0, saver Flow 20.0, Saver Time 5.00 - Drilled Uniliner Direct injection (hole at top)
Injection 1µl manual
Column ZB- Wax Plus (30m x 0.32 mm ID x 0.25µm thickness)
Oven 80 (2mins) to 160°C @ 10°C/min, hold for 2.00min, then 50°C/min to 250 for 2 minutes
FID Detector 250°C (H2 30, Air 300, Make Up N2 30.0)
Carrier Gas Nitrogen @ 3.0ml/min

I can see the IS no problem but have not seen the BHT peak.

Any suggestions??

[dblux_]

Are you sure your two compounds are separated ?

[Consumer Products Guy]

I've assayed trace BHT directly but used split injection and a non-polar capillary, and BHT is quite non-polar.

Most times, our finished products were fragranced, so for those we derivatized the BHT before injecting.

For a water matrix, I might even consider extracting the BHT to concentrate it, or just trying HPLC.

[mbdixon]

Thanks for the quick responses.

I'm pretty confident the BHT and myristic acid are not co-eluting, as the peak is the same size with the 60ppm and 3 ppm BHT std.

I do have a SGE BP1 (100% Dimethyl Polysiloxane) column sat around doing nothing in the cupboard. How will it cope with the water matrix? I might just try it anyhow....I'll stick with the splitless injection to start with a go back to split if it doesn't work.

I have been asking for a HPLC for a while as I could then do a sweep for a host of antioxidants with 1 method that we should be checking for. Getting them to invest is never easy though....

[Bigbear]

At first glance I'd say you are over loading your liner. It's counter intuitive for water injections, but you should lower the injection temp to 110-120, change to a straight 4mm liner, and inject no more than 0.5 ul.