Production and certification of candidate Pb δ-iCRMs ERM-3800 and ERM-3810 series

Abstract

This paper describes the preparation of a new type of Pb δ-isotopic Certified Reference Materials (δ-iCRMs), available in liquid form (Pb mass fraction ∼100 µg g⁻¹, 2 mL, 3% HNO₃) to prevent the risk of insufficient isotopic homogeneity. These materials are intended for the validation of δ-scale isotope ratio measurements, and come in four pairs. The quantities certified are the relative differences on values of n(²⁰⁷Pb)/n(²⁰⁴Pb), n(²⁰⁷Pb)/n(²⁰⁶Pb) and n(²⁰⁷Pb)/n(²⁰⁸Pb) ratios between the members of each pair. There is a material with ∼natural Pb-isotopic composition (ERM-3800, δ-0 material), common to all pairs, and the same ∼natural Pb progressively enriched in ²⁰⁷Pb (ERM-3810 series). Pairs I to IV are certified for δ²⁰⁷Pb values ∼ 0.01‰, 0.03‰, 0.05‰ and 0.1‰, respectively. These δ-iCRMs were produced by gravimetric mixing for which relative uncertainties (∼0.006% to 0.02%, k = 2) allowed us to guaranty no more than 0.1% (k = 2) relative combined uncertainty for the reference values of δ²⁰⁷Pb.