Has anyone ever filtered a (water) sample by means of a 0.45um nitrocellulose membrane and then froze it for future analysis? How did you go about it and do you have a reference for the method?
I used the membrane to measure chlorophyll. Fortunately you can freeze it for further analysis. Here I post the link the method you can use for this purpose.
"WATER COLUMN CHLOROPHYLL A EXTRACTION" https://tpwd.texas.gov/landwater/water/habitats/seagrass/media/qapp/Chlorophyl_a_protocol.pdf
Best to stick to standard methods for analyzing water and wastewater book. However, if you deviate, do a comparison between standard method and variant method. For some things, freezing may work well, others not. It is up to the scientist to validate results to a reasonably high level.