Chromatography Forum

Running VOCs (EPA524), and getting diminished response for 1,4-Dichlorobenzene-d4 and 4-BFB w/ respect to the other internal standards and surrogates. Area counts for these two standards slowly rise in successive levels of the calibration curve. There is also excessive carryover that needs multiple washes to get rid of. These issues do not occur when manually adding a sample fortified w/ internal standard/ surrogate directly to sparge vessel. Thinking this probably indicates contamination or active site somewhere in the pathway of the autosampler (Archon)? Flushing the autosampler with methanol, sonicating the equilibrium blocks, and replacing the water transfer line have not helped. Any suggestions to remedy this situation would be appreciated.

I would wonder about the Archon syringe, the associated valve and seals on top of it, and the 6 port valve that adds the internals - this can get rusty over time. It may be worth replacing the line that runs from the Archon to the sparge vessel.

Not familiar with that sampler. I just solved a similar problem on my Aquatek 70. When I modified the method so that there was no internal sample added, I got one of the 3 compounds I use. When I repeated this test with only MeOH in the IS vial, I got very much less of my FlBz. Come to find out the one way valve (check valve) suppling pressure to the IS vial was leaking. Replaced check valve and my problem is gone.

Thanks to you both for your suggestions. I've already replaced the water transfer line with no benefit, so that is ruled out. With regard to the Aquatek70, I'm assuming the pressure check valve is analogous to the Archon's 6-port valve. I remember checking that for leaks without finding any, but with will have another look.