Selected isotope ratio measurements of light metallic elements (Li, Mg, Ca, and Cu) by multiple collector ICP-MS

The unique capabilities of multiple collector inductively coupled mass spectrometry (MC-ICP-MS) for high precision isotope ratio measurements in light elements as Li, Mg, Ca, and Cu are reviewed in this paper. These elements have been intensively studied at the Geological Survey of Israel (GSI) and other laboratories over the past few years, and the methods used to obtain high precision isotope analyses are discussed in detail. The scientific study of isotopic fractionation of these elements is significant for achieving a better understanding of geochemical and biochemical processes in nature and the environment

The determination of the isotopic composition of Cu and Zn in seawater

The stable isotope compositions of Zn and Cu in natural materials are newly available for measurement with the advent of multiple-collector inductively coupled mass spectrometry (MC–ICPMS). Although the oceans are prime scientific targets, no progress has been made as yet because of considerable analytical challenges involving the low concentrations of these elements in seawater. We present a procedure which allows isotopic analysis of Zn and Cu isotope compositions of seawater samples at least 1 L in size by MC ICPMS.The main difficulty in analysing Zn and Cu isotopes from seawater samples is their low concentrations (nM/kg) in a matrix with much higher concentrations of other elements. We have surmounted these problems using a procedure that involves pre-concentration using either a BioRad Chelex®100 column or co-precipitation, followed by further purification and separation of Cu and Zn on an anion column. The major advantage of co-precipitation is that the blank is low and allows the precise isotopic analysis of even the most Zn-depleted surface ocean samples. Zn samples have been analysed using a double spike in order to correct for analytical mass discrimination. This approach has been tested using standard-doped seawater samples that had previously been stripped of their metal contents using the Chelex column. The approach is highly successful and yields ?66Zn = ? 0.02 ± 0.05‰ (n = 5) relative to the standard dopant. For multiple analyses of a large sample of the English Channel we obtain a result for ?66Zn of 0.35 ± 0.08‰ (n = 11) for Chelex extraction and 0.31 ± 0.04‰ (n = 5) for co-precipitation. For both Cu and Zn, correction for instrumental mass discrimination using standard-bracketing requires some care to overcome artefacts-related sample introduction into the mass spectrometer.A depth profile from the NE Pacific is also presented. Measured concentrations are very similar to those reported elsewhere. Cu and Zn isotopes in the upper 400 m of the water column are anti-correlated and may reflect the dominance of scavenging for Cu and biological recycling for Zn. <br/

The copper isotope geochemistry of rivers and oceans

We present the first extensive dataset for copper (Cu) isotopes in rivers, as well as preliminary data for estuaries and seawater. Rivers exhibit a range in dissolved δ65Cu (relative to NIST SRM 976) of + 0.02 to + 1.45 per mil (‰). The discharge-weig

The copper isotope geochemistry of rivers and the oceans

We present the first extensive dataset for copper (Cu) isotopes in rivers, as well as preliminary data for estuaries and seawater. Rivers exhibit a range in dissolved ?65Cu (relative to NIST SRM 976) of + 0.02 to + 1.45 per mil (‰). The discharge-weighted average dissolved ?65Cu and Cu concentration for the studied rivers, representing around 25% of the global riverine water discharge, are + 0.68‰ and 18.8 nmol kg? 1, respectively. Isotopic data for the dissolved phase in two small estuaries in SE England exhibit relatively minor variation through the salinity gradient (+ 0.42 to + 0.94‰) and are close to both the data for the rivers upstream from the estuaries and a measurement of the coastal sea at their mouths. Analyses of the particulate phase in the estuaries reveal a complementary light pool (? 0.24 to ? 1.02‰). The isotopic composition of the total Cu inventory is, however, close to that of the crustal source. These data, along with published constraints, suggest that the isotopically heavy dissolved phase of all the rivers originates in an isotopic partitioning of the weathered pool of Cu between a light fraction adsorbed to particulates and a heavy dissolved fraction dominated by Cu bound to strong organic complexes. Open ocean seawater samples generally exhibit even heavier dissolved Cu isotopic compositions than the riverine input (?65Cu = + 0.9 to + 1.5‰). The heavy isotopic composition of seawater is inferred to originate from intra-oceanic processes. The small dataset presented here is most consistent with further isotopic partitioning between an isotopically light pool adsorbed to particulates and a heavy dissolved pool strongly bound to organic ligands. Scavenging appears to have greatest impact in the surface ocean and least in both the oxygen minimum zone and the ocean bottom, perhaps reflecting the relative importance of scavenging, and thus the sequestration of light Cu to particulate material, at different depths.<br/