Undersized (12.5 mm diameter) glass beads with minimal amount (11 mg) of geochemical and archeological silicic samples for X‐ray fluorescence determination of major oxides

Abstract

The small glass bead technique was developed to assay precious silicic samples for geochemical and archeological analyses. Undersized (12.5 mm diameter) glass beads were prepared for wavelength dispersive X‐ray fluorescence determination of major oxides (Na2O, MgO, Al2O3, SiO2, P2O5, K2O, CaO, TiO2, MnO, and total Fe2O3). Synthetic calibration standards were prepared by compounding chemical reagents (oxides, carbonates, and diphosphate). For reliable calibration, recipe compositions of standard specimens were constructed on the basis of the evenness of plot intervals on a calibration curve. Calibration curves showed good linearity (correlation coefficient: r > 0.998). Analytical results of major oxides in granitic and basaltic rocks, obsidian, and ancient pottery were obtained with good precision (relative standard deviations were the following: <3% for more than 10.0 mass% of analyte, <5% for 1.0–10.0 mass% of analyte, and <15% for 0.1–1.0 mass% of analyte). Lower limits of detection were roughly a sub‐percentage of analyte in an unprepared sample: 0.3 mass% for Na2O, 1.0 mass% for SiO2, 0.01 mass% for MnO, and so on. The present preparation reduced the following analytical scales: (1) amount of sample from 400 mg to 11 mg (97% cutting out), (2) amount of Li2B4O7 as an alkali flux from 4000 mg to 396 mg (90% cutting out), and (3) weight of platinum crucible from 80 g to 12.5 g (84% cutting out). This small‐scale preparation might enable us to conduct destructive pretreatment of valuable and limited silicic samples such as archeological ceramics and stone tools, geochemical minerals in rock, and sediments and sand. Copyright © 2012 John Wiley & Sons, Ltd.