Treatment C. The leaching was done by dissolving the sample in 2
mL of 2 M HCl and incubating overnight, 12 h. For dry samples
that absorbed large liquid volumes, 4 mL of 1 M HCl was used instead
of 2 mL of 2 M HCl. After the incubation, 1 mL of ascorbic acid (20
g/L) and water were added to give a 10 mL total volume. This solution
was further incubated during altering sonication and thorough vortex
mixing for 2 h. Centrifugation for 10 min at 10000g followed, and if
necessary the supernatant was also ultrafiltered through a Microcon
YM-30 centrifugal filter (Millipore, Bedford, MA). The filtrate was
then injected into the IC system. Because of the acid concentration in
the leaching-treated samples, maximally 50 íL injection volumes were
used.