A PFAS delay column is installed before the injector, so it traps system-related PFAS and delays their elution. This prevents them from coeluting and interfering with the PFAS in the sample. Functionally, as the gradient starts, the trapped PFAS are eluted from the delay column and then travel to the analytical column. They arrive at the analytical column after the PFAS from the injected samples, so they do not coelute with the sample PFAS.
PFAS in the sample will elute as a normal-shaped, symmetrical peak but the delayed system-related PFAS have been continuously moving throughout the system with the gradient. They were never focused on the analytical column, so when they elute, the “peak” they generate is just an elevated baseline. You know it belongs to one or more PFAS because the signal matches the MS/MS transition of the compounds you are monitoring. However, because it is after the retention time window of the same PFAS in your sample, it’s not detected and quantitated as part of the sample.
