Sample preparation

Trace Isotopes
Geochronology
Stable Isotopes
Whole Rock Trace Element Geochemistry
Rules for Element2 Users

Trace Isotope Geochemistry

PCIGR recently published a series of papers documenting its recent work on USGS reference materials and other standards; the main aim being to achieve high-precision/accuracy in our analytical scheme. These papers also present in detail our analytical procedures.

Weis, D., Kieffer B., Hanano D., Nobre Silva I., Barling J., Pretorius W., Maerschalk C., and Mattielli N. 2007. Hf isotope compositions of U.S. Geological Survey reference materials, Geochem Geophys. Geosyst., 8, Q06006, doi:10.1029/2006GC001473.
[Abstract]

Weis D., Kieffer B., Maerschalk C., Barling J., De Jong J., Williams G., Hanano D., Pretorius W., Mattielli N., Scoates J.S., Goolaerts A., Friedman R., Mahoney J.B. 2006. High-precision isotopic characterization of USGS reference materials by TIMS and MC-ICP-MS. Geochem. Geophys. Geosyst., 7, Q08006, doi:10.1029/2006GC001283.
[Abstract]

Pretorius W., Weis D., Williams G., Hanano D., Kieffer B. and Scoates J.S. 2006. Complete Trace Elemental Characterization of Granitoid (USGSG-2,GSP-2) Reference Materials by High Resolution Inductively Coupled Plasma-Mass Spectrometry. Geostandards and Geoanalytical Research, 30(1), 39-54.
[Abstract]

Weis D., Kieffer B., Maerschalk C., Pretorius W. and Barling J. 2005. High-precision Pr-Sr-Nd-Hf isotopic characterization of USGS BHVO-1 and BHVO-2 reference materials. Geochemistry, Geophysics, Geosystems, DOI number 10.1029/2004GC000852.
[Abstract]

Goolaerts A., Mattielli N., de Jong J., Weis D. and Scoates J.S. 2004. Hf and Lu isotopic geochemistry of zircon by multiple collector inductively coupled plasma mass spectrometry. Chemical Geology, 206, 1-2 pp 1-9.
[Abstract]

U-Pb, Ar-Ar and K-Ar Geochronology

Samples for U-Pb dating are processed using a Rhino jaw crusher, a Bico disk grinder equipped with ceramic grinding plates, and a Wilfley wet shaking table equipped with a machined Plexiglass top, followed by conventional heavy liquids and magnetic separation using a Frantz magnetic separator. A number of binocular microscope work stations are available for sample picking. Most zircon fractions are air abraded prior to dissolution. The external morphology of mineral grains for analysis can be documented by SEM, and internal structure can be examined in polished grain mounts using either BSE imaging or cathodoluminescence on an SEM.

Argon Sample Preparation

Sample Mount

Stable Isotope Measurement

d18O and d13C Isotope Analysis of Carbonate Rock
Dry and finely ground carbonate mineral samples and standards are weighed into clean exetainers, which are sealed with rubber septa. The exetainers are loaded in the gas bench at 72oC and all subsequent operations are carried out using the PAL A200S autosampler. Air is removed by replacement with ultrapure helium using the autosampler, then the sample is acidified with 100% phosphoric acid. After an hour the CO2 produced by the reaction is sampled and sent to the mass spectrometer in helium, via a water trap and GC column in the gas bench. Analysis is in continuous flow mode, with CO2 gas of known isotopic composition used as the reference gas. Fractionation is calculated by multiple analysis of internal standards that have been calibrated against international standards NBS 18 and 19.

d18O and d2H Isotope Analysis of Water
Water samples are loaded into the autosampler tray with a pierceable septum on the bottle. The autosampler takes 1 microlitre and drops it into the furnace of the TC/EA. The furnace runs at 1450oC, which pyrolyses the water. The component gases are carried in continuous flow mode in helium to the mass spectrometer via a GC and Conflo III interface. CO and H2 gases of known isotopic composition used as the reference gases. Fractionation is calculated by multiple analysis of internal standards that have been calibrated against international standards SLAP and SMOW.

d15N and d13C Isotope Analysis of Solid Samples
Dried and finely ground samples packed in tin cups are introduced to an NC2500 elemental analyzer through an AS autosampler. Solid samples are combusted at 1000 degrees Celsius in a UHP O2 rich environment to form NOx, CO2, and H2O. These gases are transported in a carrier gas of UHP He to a reduction column set at 750 degrees Celsius where NOx is converted to N2. Water is removed with a trap and N2 and CO2 are separated with a gas chromatograph column. Sample combustion products N2 and CO2 are carried to an open split of a Finnigan, Conflo III where the separated gases are taken up with a fine glass capillary that leads to a Finnigan, Deltaplus mass spectrometer. Isotope ratios of nitrogen and carbon are measured and isotopic values of d15N and d13C are determined.

Whole Rock Trace Element Geochemistry

Rock samples are reduced to small chunks using a Rocklabs™ hydraulic crusher prior to final pulverization. The samples come into contact only with Tungsten Carbide plates during this stage, thereby minimizing contamination. Further grinding to yield homogenous powders suitable for acid digestion, is done in either of our Fritsch Pulverisette 5 or 6 series of electric planetary mills. The mills are equipped with between one and 4 sample holders and the use of sintered corundum further minimizes any contamination. Between sample contamination is avoided by grinding pure quartz sand, followed by grinding and subsequently discarding of a small quantity of the next sample to be milled, between samples. Samples may be ground to 1µm in order to ensure homogeneity, particularly important in PGE analyses, or when preparing coarse grained samples. Loading and acid digestion of prepared sample powders takes place in our Certified Class 100 clean laboratories, in either Savillex® PFA sample vials (i.e. hotplate digestion), or high pressure Teflon™ bombs (i.e. oven digestion) for samples that contain refractory minerals, e.g. zircon. We have optimized the ratios and mixtures of acids used for sample digestion at PCIGR in order to ensure full recovery of the complete suite of geologically relevant trace elements, irrespective of sample mineralogy and bulk rock composition. Sample powders prepared elsewhere are routinely inspected with binocular microscope in order to verify homogeneity of the powder prior to digestion. Samples are analyzed on the Element2 HR-ICP-MS for the complete suite of trace elements in Low, Medium or High resolution mode, after appropriate dilution and addition of internal standard, using either external calibration, standard addition or isotope dilution.

Rules for Element2 Users

The high resolution ICP-MS facility in the Department of Earth and Ocean Sciences, UBC is located in the basement of the EOS Main building, room 036. This facility is operated on a cost recovery basis. Use of the Element2 high resolution ICP-MS is made available to Academic collaborators (NSERC), Academic (University), Government and Industry Researchers at hourly rates of $40, $60, $75 and $100 per hour respectively. Use of the UP213 laser for laser ablation is available at an additional $20, $30, $40 and $50 per hour respectively. Assistance, training and trouble-shooting by the lab manager is also available at the same rate structure. The instrument is maintained by the lab manager who also configures the sample introduction apparatus prior to start-up, ignites the plasma, warms up the instrument, tunes and performs performance checks and mass calibrations at the beginning of the day. Daily startup and tuning usually takes 1.5 hours of instrument and manager time which are charged to the user. Thereafter the user takes over running their own blanks, standards, samples and quality control checks as necessary. The quality and acceptability of the results are the responsibility of the user; the lab and manager offer no guarantees. Because of current demand for instrument time and the facility’s mandate to provide hands-on training and experience the lab does not perform analyses on a per sample basis. Initial training requires about 3 hours time during which the instrument is not in use. This training covers theory of the instrument operation, practice, familiarization with the instrument software and often a discussion of the user’s particular analytical problem.

Practical Matters

• Samples to be introduced to the Element2 must be free of particles. Particles will lodge within the sample path preceding the mass spec and can cause increased signal noise and memory effects. Therefore, samples must be either: a) completely digested (no solid matter remaining), b) centrifuged and an aliquot diluted or c) filtered through a 0.45 um or finer filter. Filtration is the preferred method since it provides the best assurance that particles have been completely removed and only dissolved components remain.

• Dissolved organic matter in samples often causes changes in sensitivity due to differences in viscosity, plasma loading and polyatomic interferences. Organic components within the sample may also be deposited within the sample introduction lines causing poor washout and poor nebulizer performance. Self aspirating nebulizers will often stop aspirating if too much organic matter is present in a sample.

• The sample matrix must be under 0.1% dissolved solids. If you are unsure of the dissolved solids content of your samples weight out 10 g of a typical sample, dry it down and weigh what is left; it should be below 0.01 g.

• The most favourable sample matrix is 1% conc HNO3 (Seastar Baseline acid or equivalent). When using self aspirating nebulizers this concentration can be critical so any deviations from 1% HNO3 should be considered carefully and tested. Using HCl instead of HNO3 causes confounding spectral (polyatomic) interferences with chlorine 35 and 37 while H2PO4 causes rapid corrosion of the cones. HF may be added to the matrix for some elements but usually no more than 0.01% of concentrated HF.

• Internal standards must be used.

• The concentration limit for standards and samples of most elements is 100 ppb. The Element2 is a highly sensitive instrument and operates best in the ppb (parts per billion), ppt (parts per trillion) and sub-ppt concentration ranges. While it can measure ppm concentrations this usually leads to shortened detector life and contamination of the instrument sample introduction lines which precludes subsequent measurements in the ppb and ppt ranges. If you need to measure elements in the ppm range or higher then either be prepared to dilute big-time or find a more appropriate instrument for these measurements.

• Users must prepare their own matrix matched standards using the same distilled deionized water and ultraclean acids used to dilute/prepare their samples. We can supply most elemental standards at 1000 ppm concentrations from which your analytical standards can be diluted and mixed.

• Be prepared to learn that matrix matching is the shortest path to good analytical results.