Chromatography Forum

Hi all,

I'm devolping a method to analyse 6 pesticides, using the following conditions:

HPLC- Waters 2695
MS - quattro premier XE
Mobile phase; A= UpH20 + 0.1% Acetic acid/ B = Methanol + 0.1% Acetic acid

MRM - 2 transitions

I was running a 10ug/L standard to check repeatability, with good results and then after +/-10 runs, I started to lose intensity on one compound (Metaldehyde).
I already prepared the standard several times, cleaned the cone, check capillary for leaks, change column, change solvents, re-tune several times with great narrow peaks, but still having the same problem.
The other pesticides (quinmerac, carbetamide, pendimethalin, metazachlor, propyzamide) are fine with great repeatability, good peak shape and intensity.

Any ideas?

Regards

Are you injecting from the same vial over and over again?

Try preparing your standard then separating it into several vials or even one vial per injection.

Problem solved! Thanks richiekichi!