Water samples were
enriched using a freeze-dryer (Alpha1-4, Christ, Germany). A 40 mL
aliquot of each sample was transferred into a 50 mL falcon tube and
prefrozen at −20 °C overnight, followed by freeze-drying
at 15 °C and 1.65 mbar for 30 h until dryness. The residue was
reconstituted in 400 μL of acetonitrile and water (90:10, v:v),
transferred into an Eppendorf tube, and then centrifuged at 13000
min–1 for 10 min. The supernatant was then transferred
into glass vials and stored at −20 °C until analysis.
An ultrapure water blank was prepared following the same procedure.
enriched using a freeze-dryer (Alpha1-4, Christ, Germany). A 40 mL
aliquot of each sample was transferred into a 50 mL falcon tube and
prefrozen at −20 °C overnight, followed by freeze-drying
at 15 °C and 1.65 mbar for 30 h until dryness. The residue was
reconstituted in 400 μL of acetonitrile and water (90:10, v:v),
transferred into an Eppendorf tube, and then centrifuged at 13000
min–1 for 10 min. The supernatant was then transferred
into glass vials and stored at −20 °C until analysis.
An ultrapure water blank was prepared following the same procedure.
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