Determination of trace amounts of zinc, cadmium,and mercury by nitrogen afterglow emission spectroscopy

Abstract

An emission analysis for the determination of trace metals by the nitrogen afterglow is discussed. A dielectric discharge generator was employed as an excited nitrogen source. Metal salts deposited on a tantalum boat from aqueous solutions were dried in vacuo and were vaporized electrothermally. The analyte vapor was introduced into the flowing reaction cell and was excited by energy transfer from excited nitrogen molecules, mainly at the metastable triplet state N2(A3f+u). Detection limits for zinc (472.2 nm line), cadmium (326.1 nm line), and mercury (253.7 nm line) were determined to be 5, 0.1, 0.03 ng, respectively. Effects of anions on calibration curves were studied by employing metal nitrate, sulfate, and chloride. Calibration curves for cadmium salts were not affected by anions. Zinc and mercury chlorides gave weaker signals than salts with other anions. This may suggest that these chloride salts are not sufficiently dissociated. Mercury(II) nitrate could not give the calibration curve, because the signal from mercury had significant amount of noise. This is due to the spectral interference from the emission band of nitrogen monoxide produced from nitrate ion. The influence of acid concentration on peak height of title elements was studied by varying the concentration up to 0.8 M. As the concentration of acid increased, sulfuric acid and hydrochloric acid reduces the peak height, but nitric acid increased it. This suggestes that the vapor of sulfuric or hydrochloric acid is a quencher of N2(A3f+u) and nitric acid vapor effectively works during the energy transfer process. However, the reproducibility of peak height became poor at high concentrations of all acids. This may be caused by the change in the surface state of the tantalum atomizer. © 1985, The Japan Society for Analytical Chemistry. All rights reserved.