title: Stable isotope analyses of oxygen (18O:17O:16O) and chlorine (37Cl:35Cl) in perchlorate: reference materials, calibrations, methods, and interferences.
abstract: BACKGROUND
  Perchlorate (ClO4-) is a common trace constituent of water, soils, and plants; it has both natural and synthetic sources and is subject to biodegradation. The stable isotope ratios of Cl and O provide three independent quantities for ClO4-source attribution and natural attenuation studies: δ37Cl, δ18O, and δ17O (or Δ17O or17Δ) values. Documented reference materials, calibration schemes, methods, and interferences will improve the reliability of such studies.
  
  
  METHODS
  Three large batches of KClO4with contrasting isotopic compositions were synthesized and analyzed against VSMOW-SLAP, atmospheric O2, and international nitrate and chloride reference materials. Three analytical methods were tested for O isotopes: conversion of ClO4-to CO for continuous-flow IRMS (CO-CFIRMS), decomposition to O2for dual-inlet IRMS (O2-DIIRMS), and decomposition to O2with molecular-sieve trap (O2-DIIRMS+T). For Cl isotopes, KCl produced by thermal decomposition of KClO4was reprecipitated as AgCl and converted into CH3Cl for DIIRMS.
  
  
  RESULTS
  KClO4isotopic reference materials (USGS37, USGS38, USGS39) represent a wide range of Cl and O isotopic compositions, including non-mass-dependent O isotopic variation. Isotopic fractionation and exchange can affect O isotope analyses of ClO4-depending on the decomposition method. Routine analyses can be adjusted for such effects by normalization, using reference materials prepared and analyzed as samples. Analytical errors caused by SO42-, NO3-, ReO42-, and C-bearing contaminants include isotope mixing and fractionation effects on CO and O2, plus direct interference from CO2in the mass spectrometer. The results highlight the importance of effective purification of ClO4-from environmental samples.
  
  
  CONCLUSIONS
  KClO4reference materials are available for testing methods and calibrating isotopic data for ClO4-and other substances with widely varying Cl or O isotopic compositions. Current ClO4-extraction, purification, and analysis techniques provide relative isotope-ratio measurements with uncertainties much smaller than the range of values in environmental ClO4-, permitting isotopic evaluation of environmental ClO4-sources and natural attenuation. Copyright © 2016 John Wiley & Sons, Ltd.
authors.affiliation: National Research Program, US Geological Survey, 431 National Center, Reston, VA, 20192, USA.
authors.forename: J K
authors.initials: JK
authors.lastname: Böhlke
authors.affiliation: National Research Program, US Geological Survey, 431 National Center, Reston, VA, 20192, USA.
authors.forename: Stanley J
authors.initials: SJ
authors.lastname: Mroczkowski
authors.affiliation: Department of Geological Sciences, University of Delaware, Newark, DE, 19716, USA.
authors.forename: Neil C
authors.initials: NC
authors.lastname: Sturchio
authors.affiliation: Department of Geological Sciences, University of Delaware, Newark, DE, 19716, USA.
authors.forename: Linnea J
authors.initials: LJ
authors.lastname: Heraty
authors.affiliation: American Pacific, 10622 West 6400 North, Cedar City, UT, 84721, USA.
authors.forename: Kent W
authors.initials: KW
authors.lastname: Richman
authors.affiliation: American Pacific, 10622 West 6400 North, Cedar City, UT, 84721, USA.
authors.forename: Donald B
authors.initials: DB
authors.lastname: Sullivan
authors.affiliation: American Pacific, 10622 West 6400 North, Cedar City, UT, 84721, USA.
authors.forename: Kris N
authors.initials: KN
authors.lastname: Griffith
authors.affiliation: Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA.
authors.forename: Baohua
authors.initials: B
authors.lastname: Gu
authors.affiliation: Biotechnology Development and Applications Group, CB&I Federal Services, Lawrenceville, NJ, 08648, USA.
authors.forename: Paul B
authors.initials: PB
authors.lastname: Hatzinger