Novel Platinum–Nickel Composite Trap for Simultaneous and Direct Determination of Mercury and Cadmium in Soil and Its Mechanism Study

In this work, following a metal-ceramic heater (MCH) as an electrothermal vaporizer (ETV), a novel composite Pt/Ni trap based on platinizing the foamed nickel was first fabricated to trap Hg and Cd simultaneously. So, a solid sampling Hg–Cd analyzer was developed to simultaneously detect trace Hg and Cd in soil samples, mainly consisting of an MCH, a composite Pt/Ni trap, and an atomic fluorescence spectrometer (AFS). This small-size MCH-ETV system only consumes 100 W for the complete vaporization of Hg and Cd in soil matrices. The Pt/Ni trap fulfills the complete trapping of Hg and Cd following the solid sampling MCH-ETV system and then fast releases them by heating. It was proved that trapped and released Hg and Cd by the Pt/Ni trap are atomic species using X-ray photoelectron spectroscopy (XPS) and other approaches; specially, the effective cotrapping of Hg and Cd might be due to forming alloys of Hg + Pt and Cd + Ni on the Pt/Ni trap. Under the optimized conditions, the method detection limits (LODs) of Hg and Cd reached 0.4 μg/kg and 0.04 μg/kg for a 20 mg sample size, the relative standard deviations (RSDs) were within 12% and 8% for soil samples, respectively, and the recoveries ranged from 96% to 105%, indicating favorable analytical sensitivity, precision, and accuracy. The whole analysis time can be controlled within 5 min without the soil digestion process. The proposed Hg–Cd analyzer is thus suitable for rapid detection of Hg and Cd in soil samples with advantages such as simplicity, green, and safety. Further, the proposed solid sampling ETV-composite trap method has a promising application potential in the field and rapid detection for multielements.