A simple, practical methodology for routine VSMOW/SLAP normalization of water samples analyzed by continuous flow methods

Normalization of stable isotope data is important for meaningful inter-labo ratory comparisons of data, especially for waters where there may be large natural variations in isotope ratios of oxygen and hydrogen. As a result, l arge, systematic errors may arise in continuous dow applications without co rrection, whereas normalization to the VSMOW/SLAP scale can facilitate inte r-laboratory comparison and can be accomplished by a simple procedure in wh ich secondary laboratory standards, carefully calibrated, are analyzed alon g with unknown samples, Delta values for these standards, as analyzed, are plotted against the calibrated values and a linear regression is performed. The resulting equation is applied to unknown samples to achieve the normal ization. The one-sigma [1 sigma] standard deviation fur replicate samples b y this normalization method using a Finnigan Gasbenchll should be less than or equal to 0.1 parts per thousand. Because samples are analyzed directly against calibrated laboratory standards, this method also alleviates the re quirement to carefully calibrate reference gases, to carefully control abso lute temperatures for equilibration methods, or to determine H-3(+) for del ta D-VSMOW measurements. Copyright (C) 2000 John Wiley & Sons, Ltd.