Perspective: Hidden biases in isotope delta results and the need for comprehensive reporting

Abstract

Measurements of stable‐isotope composition on an isotope‐delta scale can be subject to bias between laboratories or over time within a single laboratory. This bias can arise not just from differences in method protocol but also from changes in reporting guidelines, or even to the isotope‐delta scales themselves. Without a clear description of method protocols, including all sample preparation steps, instrumental parameters and settings, data processing including calibration of results and estimation of measurement uncertainty, the traceability and comparability of isotope‐delta values cannot be assured as bias(es) may remain hidden. To address this need, there are now clear guidelines published by IUPAC for reporting isotope‐delta values for the “light” elements hydrogen, carbon, nitrogen, oxygen and sulfur.1 We recommend that authors and reviewers adhere to those guidelines when preparing and reviewing future publications.

Re‐determination of R(13C/12C) for Vienna Peedee belemnite (VPDB)

“…The situation was similar for mixture AB2 where LGC employed USGS41a and CIO used USGS41 both with a very similar carbon isotope delta value to mixture AB2 itself for calibration, while the most 13 C‐enriched RM used by JSI was USGS66. Selection of RMs certainly has the potential to result in bias between calibrated carbon isotope delta values 63 …”

“…of RMs certainly has the potential to result in bias between calibrated carbon isotope delta values. 63 The two sodium bicarbonate RMs warrant some further discussion. IAEA-303A and -303B were characterized by interlaboratory comparison in 1991 and therefore predate the adoption of the VPDB-LSVEC scale in 2006.…”