Question about C-18 extraction disks

[Mike H.]

I have just compared the system blank chromatograms for a gradient run where the mobile phase was filtered through a C-18 extraction disk and one where it was not. The blank for the filtered run is noticeably cleaner than the non-filtered blank. Why? I don't understand why mobile phase impurities would be detected as peaks when it seems like they would be masked by the background.

[tom jupille]

Explanation is here: viewtopic.php?f=31&t=19085

[Mike H.]

I had forgotten how well you are able to explain these concepts. (I took your method development online course a couple years ago.) I now think I should have started with the troubleshooting course first. Thank you.