Precise, accurate measurement of the natural Aluminium content in quartz powder, [Al], extracted from surface bedrock/sediment for in situ cosmogenic nuclide studies is critical for reliable 26Al exposure ages and 26Al/10Be ratios for burial dating. Numerous articles have cited issues regarding reliability of 26Al ages paired to 10Be ages, not only due to poor statistical error, but also due to uncertainty in [Al]. Loss of Al during aliquot preparation for ICP-OES from bulk HF solutions of dissolved quartz, or inaccurate or inefficient assay via ICP (or AA) will lead to fictitious burial ages. Long-term (~ 4 years) Al assay in HF solutions of quartz powder (NIST-165a) used as an in-house standard in our laboratory shows a limiting 1 ? of  ± 5% (n ~ 50) via ICP-OES at a commercial laboratory. The spread in paired NIST-165a duplicates measured per batch is better than ±1%. To determine the accuracy of our procedures, we prepared sets of solutions (1–10 ppm Al) from 3 different quartz powders via the standard addition method. Initial results indicate a 3-7% offset between [Al] based on the standard addition method and that based on the conventional calibration curve.

Quartz purification is essential for the successful measurement of 10Be and 26Al by AMS. The common etching technique has been an ultrasonic agitation in a dilute (~2%) HF solution. We have developed an alternative method using hot phosphoric acid (~250°C), which preferentially dissolves silicates but not quartz. Differentiation of quartz from other minerals (e.g., feldspars, plagioclase) is excellent, and usually less cycles are required than the conventional HF etching. The hot phosphoric etch method is particularly effective for rocks containing fine grain quartz, e.g., greywacke, silcrete and chert, to enhance quartz recovery. We present semi-quantitative data that compares the efficiency and the benefits of the two methods.