Pesticide determinations in water using LC-DAD

[jdb]

Good morning !
We are currently analyzing pesticides (triazines, urones) in ground water using RP-LC-DAD. Mobile phase: water/acetonitril. Until now we just used MilliQ water from a water purification system (Millipore Elix) without any buffers. Unfortunately we observe retention time differences during a sequence run. Would you suggust us to buffer the water phase ? Which buffer would you suggest ? Do we have to add buffered water also to acetonitrile ?
I very appreciate your suggestions. Thanks

Daniel

[Mark Tracy]

Any time that ionization of either the column or the analyte is an influence on the retention time, you should use a buffer. There have been many discussions of buffers on this Forum, and I recommend you look through some of the old postings first.

[ravenwork]

Greetings,

You are analyzing some organic molecules that will probably not appreciable ionize in and aqueous/organic solvent mixture. I would doubt that the absence of a buffer is causing your retention time issue, especially since you seem to state that you have some history of successful analyses with pure water. I would suspect more simple issues like pump or proportioning system failure.

When you hear hoofbeats, look for horses, not zebra.

Evan L. Cooper