The temperature dependent relationship is subtle ().
COO is a rare isotopologue (≈60 ppm [3]).
Therefore, to obtain adequate precision, this approach requires long analyses (≈2–3 hours) and very large and uncontaminated samples.
Clumped isotope analyses assume that measured Δ47 is composed of COO, the most common isotopologue of mass 47.  Corrections to account for less common isotopologues of mass 47 (e.g. COO O) are not completely standardized between labs.