Thermal Ionization Mass Spectrometers (TIMS)
The Nu TIMS was installed at PCIGR in November 2014 and is first TIMS ever commercially produced by Nu Instruments Ltd. (UK). It was designed as part of a collaborative research and development partnership between PCIGR and Nu that aims to improve analytical techniques and instrument design for the benefit of the scientific community.
The Nu TIMS is equipped with the variable dispersion multi-collector technology to improve the versatility and overall performance of this long established analytical technique. This newly designed TIMS combines advances in filament assembly, with ease of use and high precision. The Nu TIMS utilizes a patented Zoom lens system to ensure perfect peak alignment without the requirement of moving the detectors. It is equipped with an ion-counting mini Daly and an ion counter capable of precise measurement of small samples and low abundance isotopes, providing the ultimate in stability and dynamic range.
The Nu TIMS at PCIGR is used to measure Sr and Nd isotopic ratios. So far, in static mode, the average for SRM987 300ng is 0.710229 ± 26 (n=23) and for JNdi 100ng is 0.512121 ± 39 (n=12). In dynamic mode the average for SRM987 300ng is 0.710250 ± 8 (n=19) and for JNdi 100ng is 0.512107 ± 11 (n=11).
We are also experimenting with analyses with much smaller sample loads, down to <10ng for Sr and <20ng for Nd.
Thermo Finnigan Triton TIMS
The Triton TIMS was installed in April 2002 and is heavily used by the geochemical tracer lab for high-precision analyses of radiogenic isotopes. The Triton is equipped with 9 Faraday cups and one ion counter and a special matrix system for data integration that cancels out individual collector gain (virtual amplifier), thus allowing for the acquisition of high-precision analyses (<5×10-6 for 87Sr/86Sr and 143Nd/144Nd on 135 ratios [2SE, internal precision]). The barrel carries 21 samples that when running automatically for “routine” analyses (Sr, Nd) can be at a pace of a barrel every 2-3 days.
Since completion of the installation in October 2002, the UBC Triton has analyzed more than 9200 sample isotopic compositions. Initially we had an even distribution between Nd and Sr analyses but nowadays the Triton is entirely dedicated to Sr analyses. We are now on barrel number 525 (17/18 samples and 4/3 standards per barrel).
In terms of reproducibility and instrument performance, with the help of Isomass, we replaced the H3 collector in October 2003 and the running means for the standards were:
NBS 987: 0.710252 ± 12 (n=77)
La Jolla: 0.511853 ± 11 (n=91)
Then in September 2005, all the inserts of the collectors were replaced; the running means for the standards after these replacements were:
NBS 987: 0.710246 ± 17 (n=89)
La Jolla: 0.511852 ± 12 and 0.348406 ± 8 (n=50)
In January 2008, an amplifier and all the inserts of the collectors were replaced AGAIN; our new running means for the standards since January are:
NBS 987: 0.710243 ± 27 (n=114; January-September)
La Jolla: 0.511853 ± 15 and 0.348407 ± 12 (n=102)
In the fall of 2008, the NBS 987 values started creeping up again, up to barrel averages of 87Sr/86Sr = 0.710276 ± 9. We therefore changed the cup configuration and put 88Sr in H2; the NBS 987 values came back down to 0.710253 ± 21 (n =49). As the 87Sr/86Sr started climbing immediately, we shifted to 88Sr in the H1 collector and had an average of 0.710242 ± 12 (n=9). After observing a new increase in the 87Sr/86Sr ratios in the end of 2012 we replaced again the inserts of all the cups in January 2013. As of today the average is 0.710236 ± 18 (n=145). This is clearly of great concern to us and we keep monitoring the evolution of the standard ratios as well as processing complete procedural duplicates for each batch of samples.
VG54R and VG Sector 54 TIMS
The Micromass VG54R single-collector TIMS was purchased in 1982 with NSERC support and underwent major upgrades in 1987 and 1995. It is currently configured with a Faraday collector and Daly photomultiplier, the latter for low level U-Pb analyses (<1 ng radiogenic Pb), digital voltmeter and an automated 16-sample turret. This instrument is now primarily used for single grain zircon chemical abrasion (CA-TIMS) U-Pb as well as U-pb accessory phase analysis. It is also used for common Pb analysis of sulphide minerals and feldspar, Pb and U blanks from in-house produced ultrapure reagents, as well as blanks from common Pb and U-Pb studies.
This single-collector TIMS instrument with Sector 54 electronics was acquired in 2008 from the University of California at Berkeley, where it was housed in the lab of D. DePaolo. It is currently configured with an automated 20-sample turret, an oversized faraday collector (originally acquired to facilitate Ca isotopic analyses), an analogue Daly collector used for low level U-Pb analyses, a digital voltmeter and digital pyrometer. It is operated with the most recent version of Sector 54 software. Since 2009 this instrument has been used exclusively for single-grain CA-TIMS U-Pb analysis of zircon, and a variety of accessory phases. In late 2009 to early 2010 we plan to upgrade from an analogue to digital ion counting Daly detector system.
Both of these instruments support the PCIGR geochronology lab, which separates a wide range of minerals for ID-TIMS U-Pb analysis including zircon (for CA-TIMS single-grain work), baddeleyite, monazite, titanite, allanite, garnet, apatite and rutile from mafic through felsic rocks, employing standard crushing, pulverizing and wet shaker table techniques followed by heavy liquid and magnetic separations and hand picking. The PCIGR geochronology lab has been involved with the EARTHTIME initiative since 2006. During that year we acquired the three U-Pb reference solutions made available for spike calibration and used them to recalibrate the UBC mixed 205Pb-233-235U isotopic tracer. During 2008 we acquired and began to analyse the EARTHTIME synthetic solution reference materials (100 Ma, 500 Ma and 2 Ga). We continue to routinely analyse these solutions to the present time. In June 2010 we received our first aliquot of ET535 spike and in September 2015 we received a refill of this EARTHTIME isotopic tracer. This spike is used for much of the U-Pb work conducted in the lab. The relatively recent developments of U-Pb zircon work in the lab are as follows. During 2005 we moved from exclusively multi-grain fractions to single-grain work and fractions with less than about 10 grains. During 2006 and ongoing all zircon work was switched to no chemistry single-grain. In 2008 we began switching to chemical abrasion (CA-TIMS) work and by 2009 this technique was used for all zircon work. In 2008 we switched from an in-house U-Pb data reduction program to U-Pbr, an excel-based routine based on the error estimate algorithms published by Schmitz and Shoene (2007).
Since PCIGR was established in January, 2002, and through Sept 2015 the UBC U-Pb group has produced: more than 6000 U-Pb isotope dilution analyses from in excess of 1100 rock samples. More than 2000 sulphide mineral common Pb isotopic compositions and more than 2500 U-Pb standard and blank analyses.
Schmitz, M. D. and Schoene, B., (2007). Derivation of isotope ratios, errors, and error correlations for U-Pb geochronology using 205Pb-235U-(233U)-spiked isotope dilution thermal ionization mass spectrometric data, Geochem. Geophys. Geosyst., 8, Q08006, doi:10.1029/2006GC001492.