Journal
ANALYTICAL AND BIOANALYTICAL CHEMISTRY
Volume 398, Issue 7-8, Pages 3115-3125Publisher
SPRINGER HEIDELBERG
DOI: 10.1007/s00216-010-4231-5
Keywords
Zinc isotopes; Stable isotope fractionation; Soil biogeochemistry; Double-spike; Mass bias correction; MC-ICPMS
Funding
- Biotechnology and Biological Sciences Research Council [BB/C518014/1] Funding Source: researchfish
- Science and Technology Facilities Council [ST/F002157/1] Funding Source: researchfish
- BBSRC [BB/C518014/1] Funding Source: UKRI
- STFC [ST/F002157/1] Funding Source: UKRI
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Analysis of naturally occurring isotopic variations is a promising tool for investigating Zn transport and cycling in geological and biological settings. Here, we present the recently installed double-spike (DS) technique at the MAGIC laboratories at Imperial College London. The procedure improves on previous published DS methods in terms of ease of measurement and precisions obtained. The analytical method involves addition of a Zn-64-Zn-67 double-spike to the samples prior to digestion, separation of Zn from the sample matrix by ion exchange chromatography, and isotopic analysis by multiple-collector inductively coupled plasma mass spectrometry. The accuracy and reproducibility of the method were validated by analyses of several in-house and international elemental reference materials. Multiple analyses of pure Zn standard solutions consistently yielded a reproducibility of about +/- 0.05 parts per thousand (2 SD) for delta Zn-66, and comparable precisions were obtained for analyses of geological and biological materials. Highly fractionated Zn standards analyzed by DS and standard sample bracketing yield slightly varying results, which probably originate from repetitive fractionation events during manufacture of the standards. However, the delta Zn-66 values (all reported relative to JMC Lyon Zn) for two less fractionated in-house Zn standard solutions, Imperial Zn (0.10 +/- 0.08 parts per thousand: 2 SD) and London Zn (0.08 +/- 0.04 parts per thousand), are within uncertainties to data reported with different mass spectrometric techniques and instruments. Two standard reference materials, blend ore BCR 027 and ryegrass BCR 281, were also measured, and the delta Zn-66 were found to be 0.25 +/- 0.06 parts per thousand (2 SD) and 0.40 +/- 0.09aEuro degrees, respectively. Taken together, these standard measurements ascertain that the double-spike methodology is suitable for accurate and precise Zn isotope analyses of a wide range of natural samples. The newly installed technique was consequently applied to soil samples and soil leachates to investigate the isotopic signature of plant available Zn. We find that the isotopic composition is heavier than the residual, indicating the presence of loosely bound Zn deposited by atmospheric pollution, which is readily available to plants.
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