“…The glass bead specimens were prepared by fusing a mixture of the powdered sample (0.400 g) and anhydrous Li 2 B 4 O 7 (4.000 g) as an alkali flux in a Pt-Au crucible (CS-2 type, bottom inner diameter: 35 mm, Pt 95%-Au 5%) using a high-frequency electromagnetic fusion machine (Bead Sampler NT-2000, Nippon Thermonics Co. Ltd.) under the following conditions: preheat at 800°C for 120 s; melt at 1,200°C for 120 s; and melt at 1200°C for 120 s with agitation. [23] 3.2 | X-ray fluorescence spectrometry The X-ray intensities of the characteristic lines (Kα lines of Na, Mg, Al, Si, P, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Rb, Sr, Y, Zr, and Nb, Ba Lα, and Pb Lβ) from each analyte were measured using a wavelength-dispersive XRF spectrometer (RIX3100, Rigaku Corp.) equipped with an endwindow 4 kW Rh X-ray tube operated at a 50 kV tube voltage and 80 mA tube current. The measurement chamber was regulated at a vacuum of several Pa.…”