Hello all,

I tried out a new ELISA plate from ABCAM yesterday, to measure fecal IgA levels in two mouse models. The manufacturer instructions stated that PBS pH 7.2 to 7.4 can be used to prepare IgA from many different bio sample types. I used PBS prepared in our lab to isolate the fecal IgAs, and used the same PBS for serial dilutions and as a blank.

This ELISA uses "chromagen A" and "chromagen B" as the reporters (they turn blue following some horseradish peroxidase-induced reaction), and some proprietary "stop" solution that turns the blue reactions yellow. At the end of my assay, every single well containing our lab PBS, including the blank, had a similar OD reading, despite my serial dilutions ranging over a 1:3000 dilution range.

Does anyone have any idea of potential PBS contaminants that would cause such an outcome? I've attached a picture of my results, in case that is helpful. Thank you!