A modified method for biogenic silica determination
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We describe a modified method for the determination of biogenic silica (BSi) in lacustrine sediment samples with BSi concentrations >0.5% SiO2 (detection limit). To speed up the leaching procedure (48 samples per day), we suggest the use of Teflon autoclaves that can be left unattended (no stirring of the solution) for 3 h at 100°C in an oven. We suggest a volume correction by Na measurement to account for volume errors during pipetting off a hot solution. We also propose to carry out a correction for minerogenic silica by the simultaneous determination of Al in the leachate. Analytical precision and accuracy of the proposed method are 2.4% (relative standard deviation) and 70–110% recovery (relative to the mean of four international reference sediment samples), respectively. Additionally, we demonstrate that pre-treatment of the samples with H2O2 and/or HCl prior to alkaline leaching is not necessary for all samples. Due to the great diversity of lacustrine and marine sediments, however, the pre-treatment procedure should be tailored for samples from different sites.
KeywordsBiogenic silica NaOH-extraction ICP-OES Teflon autoclaves
We thank Claire Treignier, Brian Sinnet, Ingrid Holderegger, Daniel Schloz (all Eawag), for developing the method in the laboratory. Sabine Stahl (Univ. Bremen, GEOPOLAR) is acknowledged for BSi analyses of reference sediment with the timed dissolution method in Bremen. The manuscript benefited greatly from critical comments by Beat Müller (Eawag) and from the comments and suggestions of Mark Brenner and an anonymous reviewer.
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