Standardization for oxygen isotope ratio measurement - Still an unsolved problem

Numerous organic and inorganic laboratory standards were gathered from nine European and North American laboratories and were analyzed for their delta (18)O values with a new on-line high temperature pyrolysis system that was calibrated using Vienna standard mean ocean water (VSMOW) and standard ligh t Antartic precipitation (SLAP) internationally distributed reference water samples. Especially for organic materials, discrepancies between reported and measured values were high, ranging up to 2 parts per thousand. The reas ons for these discrepancies are discussed and the need for an exact and rel iable calibration of existing reference materials, as well as for the estab lishment of additional organic and inorganic reference materials is stresse d. Copyright (C) 1999 John Whey & Sons, Ltd.