Chemical State Analysis of Chromium by Mixed Resin Preconcentration-X-Ray Fluorescence Spectrometry

Abstract

A mixture of anion exchange, cation exchange and chelating resin beads shows an excellent ability to collect trace elements in water samples. Moreover, when the constituent resin beads have different adsorption characteristics and can be separated from water after concentrating reactions, the measurement of each kind of resin beads can allow chemical state analysis.
Commercially available resin beads (AG 1 X 8 Cl, AG 50 WX 8 Na and Chelex-100Na) were dried and sieved to give narrow bead size distribution. The mixture of anion exchange (200∼250 mesh, ROH, 0.2 g), cation exchange (115∼150 mesh, RH, 0.2 g) and chelating (<350 mesh CHLNa₂, 0.18 g) resin beads was added to the water sample. The resin beads were separ ated by filtration and dried under vacuum. Then, they were sieved by a 170 mesh and a 300 mesh standard sieve. Cr⁶⁺ was adsorbed by the anion-exchange resin beads. Cr³⁺ was concentrated onto the chelating and the cation exchange resin beads.It was distributed between the cation exchanger and the chelateformer when the concentration of total ions was low. With an increase in the amount of total ions, Cr³⁺ tended to be collected by the chelating resin. The separated and dried resin beads were fixed onto an adhesive tape to form a monolayer resin bead sample of excellent reproducibility. The proposed method (Fig.8) showed concentrating factors of 1000 and 500 for Cr⁶⁺and Cr³⁺ respectively. The lower detection limits were 2.3and 8∼10 ppb for Cr⁶⁺ and Cr³⁺ respectively, by a standard wavelength dispersive X-ray fluorescence spectrometer.