Simultaneous trapping of Zn and Cd by a tungsten coil and its application to grain analysis using electrothermal inductively coupled plasma mass spectrometry

Abstract

For the first time, a tungsten coil (TC) was employed to trap Zn and Cd at room temperature and release them simultaneously by heating. In this study, using porous carbon as a vaporizer and a tungsten coil as a Zn and Cd trap, a novel method of solid sampling electrothermal vaporization (SS-ETV) coupled with inductively coupled plasma mass spectrometry (ICP-MS) was developed for the direct detection of Zn and Cd in grain samples. The optimal ashing, vaporization, and releasing conditions as well as the flow rate of the 4% H₂ (v/v) and Ar mixture as the extra and carrier gases were investigated. Under the optimized conditions, the detection limits (LOD) were 1 pg for Zn and 0.1 pg for Cd; the relative standard deviations (RSD) of 11 repeated measurements were 4.7% for Zn and 7.9% for Cd using 2 mg of rice powder samples; the spiked recoveries ranged from 88% to 113%. The concentrations of Zn and Cd in wheat, corn and rice samples measured by the established method were all found to be in the range of the certified values of reference materials. Furthermore, it was proven that the vaporized and trapped species of Zn and Cd were almost atoms by atomic fluorescence spectrometry (AFS) and X-ray photoelectron spectrometry (XPS).