New Multi-Collector Mass Spectrometry Data for Noble Gases Analysis

Transcription

1 New Multi-Collector Mass Spectrometry Data for Noble Gases Analysis Alessandro Santato, 1 Doug Hamilton, 1 Jan Wijbrans, 2 Claudia Bouman 1 1 Thermo Fisher Scientific, Bremen, Germany 2 VU University Amsterdam, Faculty of Earth and Life Sciences, Amsterdam, The Netherlands

2 Overview Purpose: We test the performance of new high gain amplifiers equipped with Ω feedback resistors. The tests are carried out on the multi-collector Thermo Scientific HELIX MC Plus noble gas MS. Methods: Circa 2.4 x mole of argon was analyzed using three different multi-collector modes and 40 Ar/ 36 Ar and 38 Ar/ 36 Ar was measured. Results: The new Ω amplifier show a decisive improvement in the measurement of small samples. Introduction On the Earth, noble gases are present as rare elements and in most of the cases their concentration within samples is extremely low. Therefore their analysis requires a high detection efficiency which implies ultra high vacuum systems, mass spectrometers able to operate in static mode, and detectors capable of reading small signals. Here we present a comparison between the latest amplifiers equipped with Ω resistors and the established state-of-art Thermo Scientific detector technology, represented by: amplifiers and the latest electron multiplier: Compact Discrete Dynode (CDD). Methods Sample Preparation and Analysis Argon from atmospheric air was prepared with the Thermo Scientific NG Prep System and used as standard sample for all the tests. Circa 2.4 x mol of argon were repeatedly analyzed using three different collector configurations. Collector Configurations Argon mass 40, 38 and 36 were analyzed using three different multi-collector modes, see figure 1. FIGURE 1. Scheme showing the three different multicollector settings used in this work. 2 New Multi-Collector Mass Spectrometry Data for Noble Gases Analysis

3 40 Ar and 38 Ar were always analyzed, respectively: on a Faraday cup coupled with a Ω amplifier and on an electron multiplier CDD. The 36 Ar was analyzed with three different detector configurations: a Faraday cup coupled with the Ω amplifier, an electron multiplier CDD and a Faraday cup coupled with the latest Ω amplifier. Mass Spectrometry The Thermo Scientific HELIX MC Plus multi-collector static vacuum mass spectrometer is the ultimate solution for noble gas analysis. Equipped with a high-resolution magnetic sector analyzer and with a variable multi collector array, which incorporates 5 Combined Faraday Multiplier (CFM) detectors, and is capable of analyzing up to five isotopes of neon, argon, krypton and xenon simultaneously, at new levels of resolution. Data Analysis Thermo Scientific Qtegra Intelligent Scientific Data Solution (ISDS) was used for data acquisition and control software. Plots were made using Microsoft Office Excel Results The isotopic ratio of 40 Ar/ 36 Ar, using the Ω amplifier for 36 Ar, gave a value of 308 ± 0.90 and the standard error among the samples ranged from 1.3 to 3.09, whereas using the CDD configuration (for 36 Ar) the value of 40 Ar/ 36 Ar was ± 0.56 and a standard error among the samples ranged from 0.21 to With the new Ω amplifier, used for 36 Ar, we were able to achieve the following results: 40 Ar/ 36 Ar = ± 0.55 and a standard error among the samples ranged from 0.40 to (For this analysis the new Ω was not calibrated to the Ω). 38 Ar/ 36 Ar ratios were ± , ± and ± ; respectively for 36 Ar measured on: the Faraday cup with the Ω amplifiers, the CDD and the Faraday cup with the Ω amplifiers. Thermo Scientific Poster Note PN-SANTATO-GOLDSCHMIDT-2014-EN-0614S 3

4 FIGURE 2. Thermo Scientific HELIX MC Plus noble gas MS (right) and NG Prep System (left). FIGURE Ar/ 36 Ar AIR. Comparison among CDD/CDD, CDD/Faraday Ω amplifier and CDD/Faraday Ω amplifier. The Ω amplifier was not gain calibrated. This is why there is a bias in the absolute ratio. 4 New Multi-Collector Mass Spectrometry Data for Noble Gases Analysis

5 Calibration of the New Amplifier with a Ω Resistor The Ω amplifier is by design 10 times more sensitive than the corresponding Ω amplifier. Given this increased sensitivity, at this time, it is not possible to calibrate the new Ω amplifier with the existing cross calibration system, as is routinely done on the Ω and Ω amplifiers fitted to the Helix MC Plus. A reference / standard should be used to calibrate the Ω amplifier. FIGURE Ar/ 36 Ar AIR. Comparison among CDD/CDD, CDD/Faraday Ω amplifier and CDD/Faraday Ω amplifier. The Ω amplifier was not gain calibrated. This is why there is a bias in the absolute ratio. Current amplifier Noise Decay Ohm 0.2 fta (20 4 s 10 ppm in 2 s Ohm 50 ata (5 4 s 100 ppm in 8 s FIGURE 5. Specifications of the Ω amplifier compared with the Ω amplifier. Thermo Scientific Poster Note PN-SANTATO-GOLDSCHMIDT-2014-EN-0614S 5

6 FIGURE 6. Complete resolution of 36 Ar from the hydrocarbon interference 12 C 3 and partial resolution from the H 35 Cl. High Resolution Mass Spectrometer One of the key features of the HELIX MC Plus noble gas MS is its high resolution capability. The instrument utilizes a large radius geometry and is capable to achieve a resolution > 1500 and a resolving power > 5000 (routinely >7000) when using the high resolution entrance slit. FIGURE 7. Resolution of the three interferences of 20 Ne (top) and resolution of 21 Ne from 20 NeH (bottom). 6 New Multi-Collector Mass Spectrometry Data for Noble Gases Analysis

7 Conclusion The higher sensitivity of the new amplifiers equipped with a Ω feedback resistor represents a decisive improvement in small sample analysis. In the 40 Ar/ 36 Ar measurement the new Ω amplifier is capable of achieving a relative standard error between 0.13 and 0.44%, which represents a significant progress if compared with Ω amplifier (relative standard error is between 0.41 and 1%). The electron multiplier is the best detector in terms of sensitivity but its drift due to the variation of the yield is still a limiting factor. Future Work Further important steps in small sample analysis of noble gases will involve the development of an appropriate gain calibration technique for the new amplifiers as well as the improvement of the yield calibration for the electron multipliers during multi-collector analysis. Acknowledgements This project has received funding from the European Union s Seventh Framework Programme for research, technological development and demonstration under grant agreement no We gratefully thank Prof. Masahiko Honda from ANU Canberra for the two high resolution Neon scans. We would also like to thank the following person for their constant support: Soehnke Rathmann (test field engineer), Andreas Trint (test field engineer), Alexander Duhr (support noble gas MS), Peter Komander (electronic engineer), Michael Deerberg (R&D department) Thermo Fisher Scientific Inc. All rights reserved. Microsoft and Excel are trademarks of Microsoft Corp. All other trademarks are the property of Thermo Fisher Scientific, Inc. and its subsidiaries. Specifications, terms and pricing are subject to change. Not all products are available in all countries. Please consult your local sales representative for details. Africa Australia Austria Belgium Canada China (free call domestic) Denmark Europe-Other Finland France Germany India Italy Japan Latin America Middle East Netherlands New Zealand Norway Russia/CIS Singapore Spain Sweden Switzerland UK USA PN-Santato-Goldschmidt-2014-EN-10/16S