Instrument peak area decrease over time (PFAS Testing)


This is regarding EPA 537 PFAS testing.

On our LC MS MS we have been seeing our peak area for all our standards decrease over time, and also our signal to noise ratio has decreased which decreases our sensitivity in the instrument (over the course of a year give or take). We have had our field service engineers here and they have been cleaning the inside of the instrument and replacing parts but never really fixed our peak area/sensitivity issues to how it was when it was first installed. I am just wondering if this issue is common.

 Instrument: UPLC Acquity I Class plus and the MS is Xevo TQ-S Micro.