I have been doing the NOAA microplastics extraction on sediment samples, using NaCl for the density separation instead of lithium metatungstate (procedure says NaCl CAN be used) and then followed by the wet peroxide oxidation (typically, for 2-4 hours) using 30% hydrogen peroxide and a second density separation. The resulting material should be mostly microplastics, but I have been getting mostly organic matter. Does anyone know how I can fix this? Am i not doing the WPO long enough?

I have attached pics of the second density separation after the WPO (theoretically, everything floating should be MPs). And the resulting material from a previous procedure in the vial (the dark brown fibers were identified to be organic).

Also, how can I verify the resulting material is microplastics?

Thanks!