Three whole-wood isotopic reference materials, USGS54, USGS55, and USGS56, for δ2H, δ13C, δ15N, and δ18O measurements

Comparative measurements of stable hydrogen and oxygen isotopes in wood are hampered by the lack of proper reference materials (RMs). The U.S. Geological Survey (USGS) has prepared three powdered, whole-wood RMs, USGS54 (Pinus contorta, Canadian lodgepole pine), USGS55 (Cordia cf. dodecandra, Mexican ziricote), and USGS56 (Berchemia cf. zeyheri, South African red ivorywood). The stable isotopes of hydrogen, oxygen, carbon, and nitrogen in these RMs span ranges as δ²H_VSMOW from –150.4 to –28.2 mUr or ‰, as δ¹⁸O_VSMOW from + 17.79 to + 27.23 mUr, as δ¹³C_VPDB from –27.13 to –24.34 mUr, and as δ¹⁵N _AIR-N2 from –2.42 to + 1.8 mUr. These RMs will enable users to normalize measurements of wood samples to isotope–delta scales, and they are intended primarily for the normalization of δ²H and δ¹⁸O measurements of unknown wood samples. However, they also are suitable for normalization of stable isotope measurements of carbon and nitrogen in wood samples. In addition, these RMs are suitable for inter-laboratory calibration for the dual-water suilibration procedure for the measurements of δ²H_VSMOW values of non-exchangeable hydrogen. The isotopic compositions with 1-σ uncertainties, mass fractions of each element, and fractions of exchangeable hydrogen of these materials are:

USGS54 (Pinus contorta, Canadian Lodgepole pine)

δ²H_VSMOW = –150.4 ± 1.1 mUr (n = 29), hydrogen mass fraction = 6.00 ± 0.04 % (n = 10)

Fraction of exchangeable hydrogen = 5.4 ± 0.6 % (n = 29)

δ¹⁸O_VSMOW = + 17.79 ± 0.15 mUr (n = 18), oxygen mass fraction = 40.4 ± 0.2 % (n = 6)

δ¹³C_VPDB = –24.43 ± 0.02 mUr (n = 18), carbon mass fraction = 48.3 ± 0.4 % (n = 12)

δ¹⁵N_AIR-N2 = –2.42 ± 0.32 mUr (n = 17), nitrogen mass fraction = 0.05 % (n = 4)

USGS55 (Cordia cf. dodecandra, Mexican ziricote)

δ²H_VSMOW = –28.2 ± 1.7 mUr (n = 30), hydrogen mass fraction = 5.65 ± 0.06 % (n = 10)

Fraction of exchangeable hydrogen = 4.1 ± 0.5 % (n = 30)

δ¹⁸O_VSMOW = + 19.12 ± 0.07 mUr (n = 18), oxygen mass fraction = 35.3 ± 0.2 % (n = 6)

δ¹³C_VPDB = –27.13 ± 0.02 mUr (n = 18), carbon mass fraction = 53.3 ± 0.6 % (n = 12)

δ¹⁵N_AIR-N2 = –0.3 ± 0.4 mUr (n = 16), nitrogen mass fraction = 0.25 % (n = 4)

USGS56 (Berchemia cf. zeyheri, South African red ivorywood)

δ²H_VSMOW = –44.0 ± 1.8 mUr (n = 30), hydrogen mass fraction = 5.65 ± 0.05 % (n = 10)

Fraction of exchangeable hydrogen = 6.6 ± 0.3 % (n = 30)

δ¹⁸O_VSMOW = + 27.23 ± 0.03 mUr (n = 12), oxygen mass fraction = 41.1 ± 0.2 % (n = 6)

δ¹³C_VPDB = –24.34 ± 0.01 mUr (n = 12), carbon mass fraction = 47.3 ± 0.2 % (n = 12)

δ¹⁵N_AIR-N2 = + 1.8 ± 0.4 mUr (n = 15), nitrogen mass fraction = 0.27 % (n = 4)