The isotopic composition of VPDB

Natural variations of carbon isotope ratios are expressed relative to Vienna Peedee belemnite (VPDB) [1]. In 1998, IUPAC recommended [2] the value of the ¹³C/¹²C isotope ratio in VPDB as reported by Chang and Li [3], and this recommendation was further reaffirmed by IUPAC in 2010 [4]. However, recent measurements of carbon isotope ratios associated with VPDB have led the CIAAW to reexamine the set of reference values describing the isotopic composition of VPDB. The CIAAW now recommends the following value of the ¹³C/¹²C isotope ratio for VPDB (where the quoted uncertainty is at 95 % confidence level):

                  R(¹³C/¹²C, VPDB) = 0.011 113 ± 0.000 022

This value represents a consensus estimate from ten studies published between 1990 and 2024 from numerous independent measurement techniques. One of these studies is the work of Dunn et al. [5], which the CIAAW has identified as the best mass spectrometric measurement of the isotopic composition of carbon from a single terrestrial sample published in the peer-reviewed literature, commonly known as the “IUPAC Best Measurement.”

This revision also affects other quantities surrounding VPDB.  Values shown here, along with their associated expanded uncertainties (at 95 % confidence level), are meant to replace those recommended by IUPAC in 2010 [4, Table 2].

            δ_VPDB(¹³C/¹²C, NBS 19) = 0.001 95 (assumed exact)

            δ_VPDB(¹⁸O/¹⁶O, NBS 19) = –0.0022 (assumed exact)

            R(¹⁸O/¹⁶O, VPDB-CO₂)/R(¹⁸O/¹⁶O, VPDB) = 1.010 25 *

            R(¹⁸O/¹⁶O, VPDB)/R(¹⁸O/¹⁶O, VSMOW) = 1.030 92 *

            λ = 0.528 *

            R(¹⁷O/¹⁶O, VPDB-CO₂) = 0.000 3907 ± 0.000 0012 **

            R(¹⁸O/¹⁶O, VPDB-CO₂) = 0.002 088 39 ± 0.000 000 92

            R(¹⁷O/¹⁶O, VPDB-CO₂)/R(¹³C/¹²C, VPDB) = 0.035 16 ± 0.000 09

Asterisk identifies commonly accepted values that are assumed exact. A datafile describing the provenance of these newly recommended values is available from CIAAW website for download at https://ciaaw.org/data/vpdb-2024.xlsx.
(** The original Press Release had a value 0.000 3908 by mistake)
 

References 

1. Coplen (1994) Pure Appl. Chem. 66, 273-276; doi: 10.1351/pac199466020273
2. Rosman and Taylor (1998) Pure Appl. Chem. 70, 217-235; doi: 10.1351/pac199870010217
3. Chang and Li (1990) Chin. Sci. Bull. 35, 290-296; doi: 10.1360/sb1990-35-4-290
4. Brand et al (2010) Pure Appl. Chem. 82, 1719-1733; doi: 10.1351/pac-rep-09-01-05
5. Dunn et al (2024), Rapid Comm. Mass Spectrom. 38, e9773; doi: 10.1002/rcm.9773

(from ciaaw.org, 20 Dec 2024)