Chromatography Forum

In the last few months we have noticed a complete degradation of some carbamates in our in-house QC water samples upon preparation. We have found that the problem seems to be with our in-house RO water, as we pass all analytes if we make these QC samples in water that we purchased or got from a lab down the road. We have had our RO water tested for microbials, mycotoxins, a mineral screen, pH, conductivity, carbonate/bicarbonate, hardness-nothing is coming back as the problem. Has anyone ever experienced this issue in water samples? Does anyone have any other ideas what might be our problem? I appreciate any help you can offer, thanks in advance!

Do you preserve the water with the Acetate preservative listed in EPA531 before making the standards? If not that might help.

Residual chlorine is usually the problem though, and we have to check ours with a probe that measures total chlorine not just residual to make sure we are seeing it at low enough concentration.