[ Chemistry Lab ] [ Mass Spectrometry ] [ Sample Preparation ]
Separation of the specific elements of interest from a bulk rock sample or mineral separate is accomplished by first digesting the sample, followed by separation on one of more ion-exchange columns. Often we need to know the concentrations of the elements of interest, as well as their isotopic composition, and these may be determined to a very high precision by a method called "isotope dilution", which involves adding an enriched isotope (other than that of interest for say a radiogenic isotope determination) at the time the sample is weighed out. Digestion of silicate minerals requires HF and perhaps other acids, whereas carbonates, for example, may be dissolved in acids such as HCl. Ion-exchange chromatographic separations may involve either anion or cation exchange resins, and acids ranging from HCl to HBr to HF to water. Following separation of the specific element of interest, the "column cuts" are evaporated to dryness under very clean conditions, and then may be directly loaded onto a filament for TIMS analysis, or diluted (and probably aliquoted) for ICP-MS analysis. Blanks are run with each set to monitor processing contamination; because the amounts of the separated elements are generally in the picogram (10-12) to microgram (10-6) range, total processing blanks must be in the femtogram (10-15) to nanogram (10-9) range.
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The main chemistry lab, with graduate students Nancy Mahlen and Aaron Shultis for scale. We have the best view of any lab in the building. |
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Hot plates in the main chemistry lab - beaker cleaning, which is essential for low blanks. |
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Graduate student John Hora loading up the REE ion-exchange columns, which are used to separate the REEs for isotopic analysis. |
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We use different ion exchange columns for different elements. Here Tom Lapen is washing a small Pb column. |
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Garret Hart is shown here using one of the balances to weigh out a sample and spike, as part of his study of volcanic rocks from the Cascades. |
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Three of the HEPA-filtered evaporation boxes used to dry down "cuts" from the ion-exchange columns that contain the element of interest. We have a total of 8 of these boxes in various locations, and they are directly exhausted to the roof through the exhaust systems that are dedicated to the Radiogenic Isotope Lab. |
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All acids are distilled under clean conditions to attain the low blanks we need. These HCl and HF stills, made of pure silica glass and Teflon, respectively, sit in a clean box that is exhausted so that stray fumes do not get into the main lab. |