In studies with the 13 mm diameter membranes, the samples
were filtered using a luer-lock glass syringe of 10 mL connected to
a 13 mm diameter stainless steel filter holder (Whatman, Kent,
England). The samples were manually filtered by passage through
the nylon membranes mounted in the filter holder. After extraction,
the holder was separated from the syringe and opened. The
nylon membranes were then removed from the holder, and placed
on the spectrometer for recording the spectrum.