Pb isotope analysis of ng size samples by TIMS equipped with a 1013 Ω resistor using a 207Pb–204Pb double spike. Issue 1 (20th May 2015)

• Record Type: Journal Article
• Authors: Klaver, Martijn; Smeets, Richard J.; Koornneef, Janne M.; Davies, Gareth R.; Vroon, Pieter Z.
• Is Part Of: Journal of analytical atomic spectrometry. Volume 31:Issue 1(2016:Jan.)
• Page Start: 171
• Page End: 178
• Publication Date: 2015-05-20
• Subjects: Atomic spectra -- Periodicals; Atomic absorption spectroscopy -- Periodicals; 543.0858
• DOI: 10.1039/c5ja00130g
• Languages: English
• ISSNs: 0267-9477

Abstract

Abstract : The use of a 10 13 Ω amplifier to increase the 204 Pb signal enables high-precision, double spike Pb isotope data to be obtained for ng-size Pb samples. Abstract : The use of the double spike technique to correct for instrumental mass fractionation has yielded high precision results for lead isotope measurements by thermal ionisation mass spectrometry (TIMS), but the applicability to ng size Pb samples is hampered by the small size of the 204 Pb ion beam in the natural isotope composition analysis. To overcome this limitation, we successfully demonstrate the application of a 10 13 Ω resistor in the Faraday cup amplifier feedback loop used for the collection of 204 Pb in combination with a newly produced 207 Pb– 204 Pb double spike to correct for instrumental mass fractionation. The use of a 10 13 Ω resistor for the collection of the small 204 Pb ion beam leads to a tenfold improvement in the signal-to-noise ratio, but necessitates an external gain correction using a secondary standard and careful monitoring of the ion beam stability. SRM 981 aliquots of 5 ng display unparalleled reproducibility of 90–125 ppm (2 SD) and are in excellent agreement with recommended values: 206 Pb/ 204 Pb = 16.9404 ± 0.0016, 207 Pb/ 204 Pb = 15.4977 ± 0.0019 and 206 Pb/ 204 Pb = 36.7193 ± 0.0042 (2 SD, n = 22). Comparable high quality data have been obtained for 5 ng aliquots of geological reference materials AGV-1 and BCR-1 ( e.g. 206 Pb/ 204 Pb = 18.9399 ± 0.0011 and 18.8208 ± 0.0011 respectively), indicating that analytical blank contribution is negligible for sample sizes down to 5 ng. With further reduction in, or precise correction for, analytical blanks, the combination of the double spike technique with high-resistance amplifiers has the potential to produce highly accurate and precise (<200 ppm) Pb isotope data for samples below the ng level. This methodology will open a range of research possibilities presently impeded by the low amount of Pb available for analysis.