An IR-laser fluorination technique is reported here foranalyzing the oxygen isotope composition (
18O) of microscopic biogenic silica grains (phytoliths and diatoms).Performed after a controlled isotopic exchanged (CIE)procedure, the laser fluorination technique that allows oneto visually check the success of the fluorination reactionis faster than the conventional fluorination technique andallows analyzing
18O of small to minute samples (1.6-0.3 mg) as required for high-resolution
paleoenvironmental reconstructions. The long-term reproducibility achievedwith the IR laser-heating fluorination/O
2 18O analysis islower than or equal to ±0.26 (1 SD;
n = 99) forphytoliths and ±0.17 (1 SD;
n = 47) for diatoms. Whenseveral CIE are taken into account in the SD calculation,the resulting reproducibility is lower than or equal to±0.51 for phytoliths (1 SD;
n = 99; CIE > 5) and±0.54 (1 SD;
n = 47; CIE = 13) for diatoms. Aminimum reproducibility of ±0.5 leads to an estimateduncertainty on
18O
silica close to ±0.5. Resulting uncertainties on reconstructed temperature and
18O
formingwater are, respectively, ±2
C and ±0.5 and fit in theprecisions required for intertropical
paleoenvironmentalreconstructions. Several methodological points such asoptimal extraction protocols and the necessity or not ofperforming two CIE prior to oxygen extraction are assessed.