The dynamic range of sample size for isotope studies varies greatly. For stable isotope studies of “major elements”, which might exist at the wt. % level in samples, samples are generally not limited in size. In contrast, for studies of radiogenic isotopes, many these elements commonly exist in only trace quantities (ppt to ppm). Therefore, modern isotope geochemistry may requires isotopic analysis of picogram (10-12) to microgram (10-6) quantities of an element (to an precision of +/- 0.001% sometimes!). These stringent requirements (ultra-high precision analyses of samples you literally cannot see in the bottom of your beaker!) require that chemical processing of samples be done in a very clean environment, where sample handling, reagent preparation, and chemical separation is all done in an environment where contamination is minimized. 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.
The clean-chemistry laboratories of the ICP-MS Isotope Lab are divided into sub-labs/areas for clean sample preparation, balance room, reagent preparation and cleaning, and chemical separation in ultra-clean or non-metal environments. Very clean water is directly produced from two Barnstead Nanopure ion-exchange systems (a third is in the Mass Spectrometry Lab). A pure silica glass still is used for preparing clean HCl, which is further purified in sub-boiling Teflon stills. Other reagents, such as HNO3, HBr, and HF are purified in sub-boiling Teflon stills. Chemical separation is usually accomplished by a variety of ion-exchange chromatographic methods, all of which are done under laminar-flow (HEPA-filtered), clean-air conditions. Evaporation of separated “cuts” from the ion-exchange columns is also done in small HEPA-filtered evaporation boxes. Current chemical separation capabilities include elements used in “non-traditional” stable isotopes, including Mg, Si, Fe, and Mo, as well the radiogenic isotope systems Rb-Sr, REEs, Sm-Nd, Lu-Hf, common Pb, U-Th-Pb (long-term geochronology), and U series (U-Th; short-term geochronology).