title: Carbonate clumped isotope analyses with the long-integration dual-inlet (LIDI) workflow: scratching at the lower sample weight boundaries.
abstract: BACKGROUND
  Clumped isotope analyses (Δ47) of carbonates by dual inlet (DI) mass spectrometry require long integration times to reach the necessary high precision due to the low abundance of the rare isotopologue13C18O16O. Traditional DI protocols reach this only with large amounts of sample and/or a large number of replicates as a large portion of the analyte gas is wasted. We tested an improved analytical workflow that significantly reduces the sample sizes and total analysis time per sample while preserving precision and accuracy.
  
  
  METHODS
  We implemented the LIDI (long-integration dual-inlet) protocol to measure carbonates in micro-volume mode using a Kiel IV carbonate device coupled to a Thermo Scientific 253 Plus isotope ratio mass spectrometer without the new 1013ohm amplifier technology. The LIDI protocol includes a single measurement of the sample gas (600 s integration) followed by a single measurement of the working gas (WG) with the same integration time.
  
  
  RESULTS
  The Δ47measurements of four calcite standards over a period of 5 weeks demonstrate excellent long-term stability with a standard deviation of ±0.021 to ±0.025 ‰ for the final values of the individual aliquots. The Δ47analyses of a coral, four foraminifera and a calcite precipitated in the laboratory demonstrate that 14 replicates of 90 to 120 μg are sufficient to achieve an external precision of ±0.007 ‰ (1SE) or of ±0.013 ‰ at the 95% confidence level.
  
  
  CONCLUSIONS
  This study demonstrates that by using a Kiel IV-253 Plus system with LIDI it is possible to achieve the same analytical precision as conventional DI measurements with at least a factor of 40 less sample material. With the new 1013ohm resistor technology there is the potential to reduce the required sample material even more. This opens new avenues of research in paleoceanography, paleoclimatology, low-temperature diagenesis and other currently sample size limited applications. Copyright © 2017 John Wiley & Sons, Ltd.
authors.affiliation: Geological Institute, ETH Zürich, Sonneggstrasse 5, 8092, Zürich, Switzerland.
authors.forename: Inigo A
authors.identifier: http://orcid.org/0000-0003-1887-7380
authors.initials: IA
authors.lastname: Müller
authors.affiliation: Geological Institute, ETH Zürich, Sonneggstrasse 5, 8092, Zürich, Switzerland.
authors.forename: Alvaro
authors.initials: A
authors.lastname: Fernandez
authors.affiliation: Thermo Fisher Scientific, Hanna-Kunath-Strasse 11, 28199, Bremen, Germany.
authors.forename: Jens
authors.initials: J
authors.lastname: Radke
authors.affiliation: Geological Institute, ETH Zürich, Sonneggstrasse 5, 8092, Zürich, Switzerland.
authors.forename: Joep
authors.initials: J
authors.lastname: van Dijk
authors.affiliation: Ziggurat GmbH, Rainstrasse 56, 8712, Stäfa, Switzerland.
authors.forename: Devon
authors.initials: D
authors.lastname: Bowen
authors.affiliation: Thermo Fisher Scientific, Hanna-Kunath-Strasse 11, 28199, Bremen, Germany.
authors.forename: Johannes
authors.initials: J
authors.lastname: Schwieters
authors.affiliation: Geological Institute, ETH Zürich, Sonneggstrasse 5, 8092, Zürich, Switzerland.
authors.forename: Stefano M
authors.initials: SM
authors.lastname: Bernasconi