Propiconazole background in LC/MS

[djacqo]

Hi everyone,

I'm measuring propiconazole by triple quad LC/MS using a Shimadzu 8060. I've noticed that there is a persistent background for this analyte, typically around 0.2 - 1 ng/mL. I have looked at every possible MRM transition I can find and it always matches propiconazole exactly in terms of ion ratios an retention time.

This happens with just gradient/no injection runs as well. Flushing the LC system with IPA/MeOH/MeCN has no effect, and neither does changing the column. Furthermore, the intensity is highest with the first injections. This all suggests that it is a contamination in the mobile phase or system tubing, but it would be very odd to have a residual pesticide in those.

I've seen data from other labs and other instrument manufactuers where people see the same thing. Anyone have a similar experience, and if so, were you able to fix it? We're trying to move this analyte to GC/MS (where this problem does not exist) but we lose a lot of analyte in our cleanup step and cannot seem to achieve the sensitivity we need.

Thank you!

[James_Ball]

Are you using a gradient elution?

If the problem is some contaminate in the flow path prior to the syringe, then it may be possible to move the position of the peak using a delay column as is used in PFAS analysis. You would put a column with similar phase in line between the pump and the autosampler, this would capture the interfering compound and hold it until the gradient elutes if from the delay column so it will elute later in the run separate from the analyte of interest. Give it a try and it will tell you if it is an impurity in the mobile phase or leaching from the pumps instead of just something contaminating the autosampler or tubing between the autosampler and column.

[richiekichi]

I take you've tried different batches of mobile phase solvent?

I had a similar problem with Dalapon (2,2-Dichloropropionic acid) a year or so back (coincidently on a Shimadzu 8060). For us it was some kind of contamination in a particular batch of methanol. Initially we switched supplier but upon returning to the original brand, the contamination was no longer present.