Determination of trace cadmium in zinc concentrate by liquid cathode glow discharge with a modified sampling system and addition of chemical modifiers for improved sensitivity

摘要

In this work, a sampling system of liquid cathode glow discharge (LCGD) was developed for the highly sensitive determination of Cd in digested Zn concentrate samples, in which buffer bottle was used to eliminate the pulsation of peristaltic pump and increase the stability of discharge, and six-port valve injection system was employed to ensure the continuity of discharge and improve the precision and speed of analysis. The results showed that the flow rate of modified LCGD is reduced to 2.4 mL min(-1) from the previous 4.5 mL min(-1). The presence of anions and cations does not significantly interfere with the detection of Cd. Compared with the addition of no chemical modifier, the net intensity of Cd with 0.15% hexadecyltrimethylanimonium bromide (CTAB) and 18% formic acid is improved by 2.4- and 2.7-fold, respectively. The relative standard deviations with 18% formic acid, 0.15% CTAB and no chemical modifier are 0.87%, 2.01% and 2.39%, respectively. The sensitivity of Cd is improved with the addition of chemical modifiers by factors of 4.5 for 18% formic acid and 2.6 for 0.15% CTAB. The LOD with 18% formic acid for Cd is arrived at 0.0049 mg L-1 which improved by 2.7 times. The results measured by modified LCGD-AES are in accordance with the reference value as well as verification values measured by ICP-AES. In addition, the recoveries are in the range of 96.5-105.4%. The accuracy, reliability and practicality can satisfy the requirements of monitoring of trace Cd in complex samples.