Mineral particles and other contaminants cause a serious and undesirable shift in δ 18O values of biogenic silica and should be removed prior to isotope analysis. This problem is particularly significant in the fraction containing clay particles and therefore the fraction <10μm is generally avoided. Here, we present an updated preparation protocol for the <10μm fraction based on known methods, developed using test material from short cores of Lake El'gygytgyn, NE Russia. New contamination assessment and correction techniques are discussed. Best results (low initial weight/high precision and throughput rate) for the <10μm fraction were achieved using geochemical mass-balancing and determining the "percentage of contamination" by analysing the sample's and end-member's Al 2O 3 with improved Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) and Energy-Dispersive X-ray Spectroscopy (EDS) protocols or by determining the factor for calculating the percentage of contamination from the Al 2O 3 percentage of clay assemblages. Despite using small initial weights for ICP-OES (10mg) and EDS analysis (<0.5mg) a sufficiently high precision (for low Al 2O 3 percentages between 0.1 and 1.5%) could be achieved.For the >10μm fraction, point-counting under the light microscope was the preferred option. The different size-fractions from Lake El'gygytgyn samples show a distinct and significantly different species composition (average counts: <10μm: >90% Cyclotella ocellata complex; >10μm: >60% Pliocaenicus seczkinae). Differences in the oxygen isotope composition of these different size fractions could be explained by a species-effect on the δ 18O values. However, this species-effect disappeared after the correction (avg δ 18O <10μm: 19.8±0.6‰; >10μm: 19.8±0.4‰). By comparing these δ 18O values with additional recent water samples, an average 1000 ln α of 39.6‰ for Lake El'gygytgyn sub-recent diatoms was calculated. This "tool-kit" provides support for the presented improved contamination assessment and corrections and allows utilising smaller initial weight (app. 10mg) and small fractions (<10μm) for gaining corrected, higher resolution δ 18O records. © 2012 Elsevier B.V..