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Techniques and Methods 10–C2

Determination of the (18O/16O)of Water: RSIL Lab Code 489

U.S. Geological Survey

By Kinga Révész and Tyler B. Coplen

Chapter 2
Section C, Stable Isotope-Ratio Methods
Book 10, Methods of the Reston Stable Isotope Laboratory


Summary of Procedure

The purpose of the technique described by the Reston Stable Isotope Laboratory (RSIL) lab code 489 is to present a method to determine the δ(180/160), abbreviated as δ180, of water. This δ18O measurement of water also is a component of National Water Quality Laboratory (NWQL in USGS) schedules 1142 and 1172. Water samples are loaded into glass sample containers on a vacuum manifold to equilibrate gaseous CO2 at constant temperature (25°C) with water samples. After loading water samples on the vacuum manifold, air is evacuated through capillary to avoid evaporation, and CO2 is added. The samples are shaken to increase the equilibration rate of water and CO2. When isotopic equilibrium has been attained, an aliquot of CO2 is extracted sequentially from each sample container, separated from water vapor by means of a dry ice trap, and introduced into a dual-inlet isotope-ratio mass spectrometer (DI-IRMS) for determination of the δ18O value. There is oxygen isotopic fractionation between water and CO2, but it is constant at constant temperature. The DI-IRMS is a DuPont double-focusing mass spectrometer. It has a double collector. One ion beam passes through a slit in a forward collector and is collected in the rear collector. The other ion beams are collected in the front collector. The instrument is capable of measuring mass/charge (m/z) 44 and 45 or 44 and 46 by changing the ion-accelerating voltage under computer control. The ion beams from these m/z values are as follows: m/z 44=CO2=12C16O16O, m/z 45=CO2=13C16O16O primarily, and m/z 46 = CO2=12C16O18O primarily. The data acquisition and control software calculates δ18O values.

Table of Contents

Forward

Conversion Factors

Acronyms, and Abbreviations

Summary of Procedure

Reporting Units and Operational Range

Reference Materials and Documentatione

Reference Materials Used, Storage Requirements, and Shelf Life

Documentation

Labware, Instrumentation, and Reagents

Sample Collection, Preparation, Analysis, Retention Times, and Disposal

Sample Containers, Preservation, and Handling Requirements

Sample Preparation and Time Requirements

Performing the Analysis and Time Requirements

Problematic Samples

Interferences

Troubleshooting and Bench Notes

Maintenance and Maintenance Records

Sample Retention Time and Disposal

Data Acquisition, Processing, Evaluation, Quality Control, and Quality Assurance

Laboratory Information Management System for Light Stable Isotope (LIMS-LSI)

Quality-Control (QC) Samples

Acceptance Criteria for all QC Samples

Corrective Action Requirements

Responsible Parties for All QA/QC Functions for Procedures Covered in RSIL SOPs

Data Management and Records

Health, Safety, and Waste-Disposal Information

Applicable Health and Safety Issues

Personal Protection

Electrical Hazards

Chemical Hazards

Gas Cylinder Handling

Specific Waste-Disposal Requirements

Revision History

References Cited

Apendixes

Suggested citation:

Révész, Kinga, and Coplen, Tyler, B., 2008, Determination of the δ(180/160), of water: RSIL lab code 489, chap. C2 of Révész, Kinga, and Coplen, Tyler B., eds., Methods of the Reston Stable Isotope Laboratory: U.S. Geological Survey Techniques and Methods, 10–C2, 28 p.


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