TIMS: High Precision Cr TRITON Plus Isotope Analysis with Virtual Amplifier

Importance of the Topic

High precision chromium isotope analysis by thermal ionization mass spectrometry plays a critical role in tracing physico-chemical processes in planetary formation and environmental systems Chromium has four stable isotopes whose small mass-dependent anomalies at the ppm level yield insights into solar system chronology and environmental sources

Study Objectives and Overview

This application note evaluates the precision accuracy and throughput of chromium isotope analyses on a Thermo Scientific TRITON Plus TIMS in static multicollection mode using a virtual amplifier The goal is to achieve comparable external reproducibility to literature values while reducing total analysis time by more than a factor of three

Methodology and Instrumentation

• Instrument Thermo Scientific TRITON Plus Thermal Ionization Mass Spectrometer configured with zoom ion optics and Faraday cup array
• Virtual amplifier scheme employs rotation of 1011 Ω current amplifiers across four chromium isotopes and one internal standard cup to average out stochastic gain biases
• Sample preparation and loading MERCK chromium ICP standard applied to a single rhenium filament with silica gel boric acid and aluminium additives followed by staged outgassing at 3.2 A and 3.5 A
• Acquisition static multicollection with inter-block amplifier-cup switching at millisecond intervals to ensure each amplifier measures each isotope multiple times
• Operating conditions filament temperature 1200-1250 °C baseline integration and exponential mass bias correction using 52Cr 50Cr normalization

Main Results and Discussion

External reproducibility for 53Cr 52Cr ratios reached 4 ppm and 54Cr 52Cr ratios 15 ppm (2 RSD n=10) in under 2.5 hours compared to ~8 hours in previous studies Increasing cycles of amplifier-cup rotation beyond three yielded no further improvement Residual correlation between mass bias corrected 53Cr 52Cr and 54Cr 52Cr ratios was within analytical uncertainty indicating negligible nonideal fractionation under these conditions

Benefits and Practical Applications

• Threefold reduction in analysis time increases sample throughput in planetary and environmental laboratories
• High external reproducibility enables precise detection of subtle isotopic anomalies in geological meteorite and environmental samples
• Virtual amplifier approach enhances calibration stability without mechanical realignment of cups

Future Trends and Potential Applications

Extension of virtual amplifier techniques to other isotope systems and integration with automated filament loading could further boost throughput Continued long-term validation will establish suitability for routine QA QC environmental monitoring and cosmochemistry studies Miniaturization of sample preparation may allow high precision analysis of sub-nanogram chromium loads

Conclusion

The static multicollection mode with virtual amplifier rotation on the TRITON Plus delivers high precision chromium isotope data in significantly shorter time frames This method validates the stability of the amplifier and cup system and opens avenues for rapid routine analyses of diverse sample types

Used Instrumentation

• Thermo Scientific TRITON Plus Thermal Ionization Mass Spectrometer
• Virtual amplifier scheme with 1011 Ω Faraday amplifiers
• Zoom ion optics and multicollection Faraday cup array
• Single rhenium filament assembly

Reference

1. A Trinquier J-L Birck C J Allegre J Anal At Spectrom 2008 23 1565–1574
2. D Tuttas J B Schwieters Thermo Fisher Scientific Application Note 30015
3. W R Shields et al J Res Natl Bur Stand 1966 70A 193–197