Quartz purification for in-situ ¹⁰Be and ²⁶Al. For many geological applications of in-situ ¹⁰Be and ²⁶Al in quartz, the first processing steps consist of crushing and grinding rock samples and sieving to a suitable grain size fraction (e.g., 250-500 μm). Paramagnetic and heavy minerals are removed by Frantz magnetic and heavy-liquid separation, respectively (check out USGS Open-File Report 2016-1022 for a comprehensive explanation of these techniques). Chemical leaching in HCl or acetic acid removes any calcite present in the sample.

The resulting mineral separate consists mostly of quartz and feldspar. Feldspar can be chemically removed by repeated leaching in a HCl-H₂SiF₆ mixture (Merchel et al., 2019) or by froth floatation (Sulaymonova et at., 2018). Quartz is further purified by leaching in diluted (2-4%) HF, which also etches the quartz grains and removes 'meteoric' (i.e., atmospherically produced) ¹⁰Be.

About 20 g of cleaned quartz is weighted, spiked with a ⁹Be carrier, and dissolved in concentrated HF at room temperature. We use the Phena EA ⁹Be carrier with a concentration of (2246±11) μg ⁹Be/(g solution) and a ¹⁰Be/⁹Be ratio of ∼1E-16 (Merchel et al., 2013). To bring the sample solution into chloride form HClO₄ is added, the solution is boiled down on a hotplate, and the residue is dissolved in HCl.

Meteoric ¹⁰Be samples, deep-sea Mn crusts, and other samples. For meteoric ¹⁰Be applications, Be is extracted from the reactive Fe,Mn-oxyhydroxide phases on the surface of the mineral grains by leaching soil or sediment samples with a solution of NH₂OH⋅HCl in acetic acid (Bourles et al., 1989, Gutjahr et al., 2007). Some materials can be dissolved in HCl (e.g., iron meteorites or deep-sea Mn crusts and nodules) or in HNO₃/H₂O₂ (e.g., organic samples); for other materials total fusion, e.g., by microwave digestion, may be necessary to bring the sample into solution.

Once the sample is in solution, we use a combination of ion exchange chromatography and hydroxide precipitation to separate the element(s) of interest from the matrix. Some elements (Fe, Mn, Be, Al, Ti) form insolable hydroxides at pH≥8, which can be separated from the elements that stay in solution (Na, K, Ca, B) (e.g., Ochs and Ivy-Ochs, 1997).

We use Dowex 1x8, mesh 100-200 anion exchange resin (see here for a brief introduction to ion exchange chromatography) to separate Fe and Dowex 50Wx8, mesh 100-200 cation exchange resin to separate Be and Al. For actinide (Pu, U, Cm, Am) separation we use different extraction chromatographic resins including Eichrom TEVA, UTEVA, TRU and DGA resins.

After chemical processing, the sample consists of <1 mg of the target element in its hydroxide form. For actinide analysis or carrier-free Be measurements, the last processing step is a co-precipitation of the target element with a carrier Fe-solution. Other chemical separation techniques are used for the preparation of Ca, Cl, or I samples.

The sample is transferred to a quartz crucible and dried at 80°C, then calcinated in the muffel oven to transform the hydroxides into oxides (e.g., 1 h at 900°C). For Be and Al analysis the oxides are weighted and mixed with metal powder (Nb:BeO ∼4:1; Ag:Al₂O₃ ∼1:1). The sample material is then pressed into a cathode for AMS measurement.