Sample preparation is a critical yet time consuming step in many cosmogenic nuclide applications. We have developed an efficient and robust mineral separation and chemistry procedure. Mineral separation involves sizing to 0.25 - 0.50 mm and cleaning in aqua regia. A rolling drum magnetic separator rapidly removes iron-bearing minerals. To separate feldspar and mica we use a froth flotation method adapted from industrial applications. After pretreatment with dilute hydrofluoric acid the sample is mixed with dilute lauryl amine in carbonated water. In this solution the quartz is hydrophilic while other silicates are hydrophobic and attach to CO2 bubbles in the froth. The sample is etched in dilute HF/HNO3 in an HDPE bottle on heated rollers. We use commercial hotdog cookers. Gravimetric separation of rutile, garnet, and zircon is done using LST. The quartz elemental abundance is characterized using ICP-MS. The elements assayed are Al, Be, Mg, Ca, Fe, and Ti. Knowing the elemental abundances gives us the flexibility to tailor chemistry procedures for individual samples. After dissolution and spiking with low-level Be carrier, a small aliquot is taken for subsequent measurement of the Al concentration. The sample is dried in H2SO4 to expel fluorides. In most situations the sample is precipitated as a hydroxide, dissolved in oxalic acid, and introduced onto stacked cation/anion exchange columns. Be is eluted from the cation column in HCl, and Al is eluted from the anion column in an oxalic/HCl solution. We have found the oxalic acid separation to be robust against high concentrations of Al, Ti, and Fe. Our new multi-step mineral separation procedure has improved the quartz purity at Prime Lab. In particular, the addition of froth flotation and the use of hotdog cookers have reduced the time involved and volume of waste generated in quartz separation. The use of ICP-MS allows us to choose the most efficient methods for separation and purification of Al and Be.
See more of Poster Session II
See more of The 10th International Conference on Accelerator Mass Spectrometry (September 5-10, 2005)