PFAS Internal standard issue

[ddambo]

We are experiencing high recovery of d3-N-EtFOSAA (internal standard), d5-N-EtFOSAA (surrogate) and N-EtFOSAA (analyte). Instrument calibrating fine and continuing calibration checks are fine. Only happening in extracted samples randomly. We initially thought it might be the preservative (Trizma) but are now leaning toward something to do the DI water or extraction cartridge. Has anyone experienced anything similar. thank you.

[wss]

Not sure what might be the issue, but I recall that the FOSAA compounds were the most sensitive to pH adjustment during extraction. If it was a bit too basic or acidic you could see a marked effect on the recovery. The exact pH range will depend on your method though.

How well is your calibration matched to your matrix (e.g. pH, solvent composition, etc.)?

[ddambo]

All samples and batch QC are preserved with Trizma to produce a pH near 7.0 in reagent water. It also removes free chlorine in finished drinking water which is what we are primarily analyzing. Since the calibration is not extracted it does not go through the extraction process.

[James_Ball]

If it is a matrix effect you may need to run some preserved blank water through the extraction process then use that as the diluent for the calibration standards to make them matrix matched.

We have to do this for 525.3 since something in the matrix causes the responses for the last surrogate to almost double. If the standards are made in pure solvent then the extracted samples have almost 200% recovery. It is listed as a option in several drinking water methods, maybe it will help with this one.