USGS42 and USGS43: Human-hair stable hydrogen and oxygen isotopic reference materials and analytical methods for forensic science and implications for published measurement results

Because there are no internationally distributed stable hydrogen and oxygen isotopic reference materials of human hair, the U. S. Geological Survey (USGS) has prepared two such materials, USGS42 and USGS43. These reference materials span values commonly encountered in human hair stable isotope analysis and are isotopically homogeneous at sample sizes larger than 0.2 mg. USGS42 and USGS43 human-hair isotopic reference materials are intended for calibration of delta H-2 and delta O-18 measurements of unknown human hair by quantifying (1) drift with time, (2) mass-dependent isotopic fractionation, and (3) isotope-ratio-scale contraction. While they are intended for measurements of the stable isotopes of hydrogen and oxygen, they also are suitable for measurements of the stable isotopes of carbon, nitrogen, and sulfur in human and mammalian hair. Preliminary isotopic compositions of the non-exchangeable fractions of these materials are USGS42(Tibetan hair)delta H-2(VSMOW-SLAP) = -78.5 +/- 2.3 parts per thousand(n = 62) and delta O-18(VSMOW-SLAP) = +8.56 +/- 0.10 parts per thousand (n = 18) USGS43(Indian hair)delta H-2(VSMOW -SLAP) = -50.3 +/- 2.8 parts per thousand(n = 64) and delta O-18(VSMOW-SLAP) = +14.11 +/- 0.10 parts per thousand(n = 18) Using recommended analytical protocols presented herein for delta H-2(VSMOW-SLAP) and delta O-18(VSMOW-SLAP) measurements, the least squares fit regression of 11 human hair reference materials is delta H-2(VSMOW -SLAP) = 6.085 delta O-18(VSMOW-SLAP) = 136.0 parts per thousand with an R-square value of 0.95. The delta H-2 difference between the calibrated results of human hair in this investigation and a commonly accepted human-hair relationship is a remarkable 34 parts per thousand. It is critical that readers pay attention to the delta H-2(VSMOW-SLAP) and delta O-18(VSMOW-SLAP) of isotopic reference materials in publications, and they need to adjust the delta H-2(VSMOW-SLAP) and d18OVSMOW-SLAP measurement results of human hair in previous publications, as needed, to ensure all results on are on the same scales. Published by Elsevier Ireland Ltd.