Improved water δ2H and δ18O calibration and calculation of measurement uncertainty using a simple software tool.

The calibration of all δ(2)H and δ(18)O measurements on the VSMOW/SLAP scale should be performed consistently, based on similar principles, independent of the instrumentation used. The basic principles of a comprehensive calibration strategy are discussed taking water as example. The most common raw data corrections for memory and drift effects are described. Those corrections result in a considerable improvement in data consistency, especially in laboratories analyzing samples of quite variable isotopic composition (e.g. doubly labelled water). The need for a reliable uncertainty assessment for all measurements is discussed and an easy implementation method proposed. A versatile evaluation method based on Excel macros and spreadsheets is presented. It corrects measured raw data for memory and drift effects, performs the calibration and calculates the combined standard uncertainty for each measurement. It allows the easy implementation of the discussed principles in any user laboratory. Following these principles will improve the comparability of data among laboratories.