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Anal Chem

Title:		Caution on the use of liquid nitrogen traps in stable hydrogen isotope-ratio mass spectrometry
Author(s):		Coplen TB; Qi H;
Address:		"U.S. Geological Survey, 431 National Center, Reston, Virginia 20192, USA. tbcoplen@usgs.gov"
Journal Title:		Anal Chem
Year:		2010
Volume:		82
Issue:		18
Page Number:		7849 - 7851
DOI:		10.1021/ac101570f
ISSN/ISBN:		1520-6882 (Electronic) 0003-2700 (Linking)
Abstract:		"An anomalous stable hydrogen isotopic fractionation of 4 per thousand in gaseous hydrogen has been correlated with the process of adding liquid nitrogen (LN(2)) to top off the dewar of a stainless-steel water trap on a gaseous hydrogen-water platinum equilibration system. Although the cause of this isotopic fractionation is unknown, its effect can be mitigated by (1) increasing the capacity of any dewars so that they do not need to be filled during a daily analytic run, (2) interspersing isotopic reference waters among unknowns, and (3) applying a linear drift correction and linear normalization to isotopic results with a program such as Laboratory Information Management System (LIMS) for Light Stable Isotopes. With adoption of the above guidelines, measurement uncertainty can be substantially improved. For example, the long-term (months to years) delta(2)H reproducibility (1sigma standard deviation) of nine local isotopic reference waters analyzed daily improved substantially from about 1 per thousand to 0.58 per thousand. This isotopically fractionating mechanism might affect other isotope-ratio mass spectrometers in which LN(2) is used as a moisture trap for gaseous hydrogen"
Keywords:
Notes:		"PubMed-not-MEDLINECoplen, Tyler B Qi, Haiping eng 2010/08/20 Anal Chem. 2010 Sep 15; 82(18):7849-51. doi: 10.1021/ac101570f"