Two milliliter of DI water, followed by 3 mL of 30% H
2
O
2
,
were added to the samples and they were heated until efferves-
cence subsided. Additional 1 mL aliquots of H
2
O
2
were added
until effervescence was minimal. The samples were then re-
fluxed for 15 min in 10 mL of concentrated HCl. The digests
were filtered through Whatman no. 40 paper layered with
Whatman 2V fluted filters (Florham Park, NJ, USA)