The class 100 clean-chemistry room contains five laminar-flow stations, two PVC-lined exhaust hoods, and a custom-made acrylic chamber which houses two-bottle distillation vessels of the Mattinson design. The clean-chemistry laboratory is capable of supporting six scientists at work simultaneously and each workstation has within it an evacuated chamber wit hot plate so that U and Pb eluates may be evaporated to dryness in a clean-air environment. Air quality to the mass spectrometry and clean-chemistry laboratories is achieved by three stages of filtration prior to final passage through HEPA filters. Air to the laboratories is delivered via a system of ducts, with direct-drive blowers, independent of the building supply.
The Geochronology Laboratory at Washington University is a facility specializing in high-precision U-Pb geochronology by the isotope dilution method. Small sample sizes (<100 pg Pb) and exacting, time-consuming purification procedures require that most of our isotope ratio measurements be made manually; typical zircon samples (single-crystal and small multi-grain fractions) range in weight between 1-50 micrograms. Use of a clean 205Pb/235U tracer solution (205Pb/204Pb > 100,000) facilitates analysis by eliminating the need for independent isotope concentration and composition measurements.Precise and reliable ages are determined for high-quality grains cleaned with distilled reagents after prolonged abrasion treatment. Sample to background ratios are uniformly high because our low total-procedure blanks for Pb and U typically average between 1-5 pg and <1 Pb, respectively. The Geochronology Laboratory operates with 36 TFE teflon digestion vessels for dissolution of zircon, an assortment of PFA Teflon vessels for digestion of sphene, monazite, and baddeleyite, numerous ion exchange columns for element purification, and two aliquots of ultra-clean 205Pb/235U enriched tracer solutions.