diisooctyl phthalate contamination located to HESI source

[Arne]

Wanted to share this:

We've had terrible problems with phthalate contamination in our positive mode chromatograms. We see very abundant ions at 149 m/z (phthalic anhydride, fragment of 391), and 391,413,429 (diisooctyl phthalate +H,+Na,+K).

We replaced many parts on the LC and flushed and cleaned it very carefully but to no avail. We even moved the instrument to a different room to see if it was the lab air. We then used a different LC and the contaminant signal was almost exactly the same.

That's how we located the problem to our heated ESI source (HESI). Likely, the phthalate is evaporating from source parts other than the actual spray needle assembly, which was replaced with no ensuing change in contaminant level.

After starting the instrument, the signal from the ion at 391 m/z continues to increase over several 10s of minutes (long after the needle temperature readback has stabilized at 300C) until the whole source housing has equilibrated to a temperature that is hot to the touch. We will now clean the source housing and metal sheath encasing the spray needle.

This is a source of contamination is something I have never seen before and took a long time to pin down.

has anyone seen this problem? Where did it stem from? How did you clean the source and solve the problem?

[bunnahabhain]

I did not see the most obvious source for such a contamination in your list: The eluents.
- Did you swith manufacturer of your solvents?
- Did you change your solvent lines? Was your HPLC degasser serviced and has a new membrane? (OK these might not be the reaseon because you already tried two different HPLC systems)
- Did you switch to an other supplier for membrane filters for filtration of eluents? Everything that comes into contact with your solvents might be a source for plasticizers.

Good luck!
Jörg

[Arne]

Hi Joerg,

we already addressed all of your suggetions. We changed solvents, all lines, and bypassed the degasser. Thanks anyway!

Has anyone else had a contaminated source adn how did you clean it?

[Klaus I.]

If I understood you correctly you have already replaced the complete H-ESI probe? I’m assuming ion transfer capillary is also replaced.

Did you tried to disconnect the drain line from the ion source housing?
Did you analyzed a huge load (or high concentrations) of phthalates recently? Maybe the ion optic after the ion transfer capillary is dirty.
I have never heard that before, but maybe there is a problem with the lines for sheath gas and aux gas?

Good luck!

[Arne]

Hello,

the source of the phthalate contamination was the tubing leading to the drain line, as Klaus had suggested. We replaced the tubign with new, phthalate-free tubing and the problem is all but gone.

The issue was difficult to identify since there was a "lag time" between the removal of the tubing and the disappearance of the phthalate ion at m/z 391.

Thank you so much for your advice!

Arne

[Consumer Products Guy]

Reminds me of the time about 2 decades ago when we thought we had dioctyl phthalate contamination in a pilot batch of product. We didn't have dioctyl phthalate standard to match up, so we extracted Tygon tubing and matched up v. its plasticizer.