Determination of Cadmium and Zinc in Soil Samples Using Magnetic Field-Assisted Solution Cathode Glow Discharge

A magnetic field-assisted solution cathode glow discharge (MF-SCGD) was established and then applied for the detection of Cd and Zn in soil samples. In order to reveal the signal enhancement mechanism of the magnetic field, the influence of the magnetic field strength on plasma parameters, such as electron temperature and electron density, was investigated. The results showed that adding a 0.5 T magnetic field significantly reduces the red-hot degree of the Pt needle, decreases the volume of the plasma torch, extends the lifespan of the Pt needle, and widens the application range of voltage. The optimal operating parameters of MF-SCGD were identified as a 0.5 T magnetic field, 680 V discharge voltage, 3.2 mL/min solution flow rate, and pH 1.0 HNO₃ as the supporting electrolyte. Under optimal conditions, the intensities of Cd and Zn signals increased by 1.7 and 1.8 times, respectively. The limits of detection were 9.1 μg/L for Cd and 12.0 μg/L for Zn. After adding a 0.5 T magnetic field, electron temperature slightly decreased while electron density increased. The plasma parameter β was found to be less than 1, indicating that signal intensity enhancement is due to magnetic confinement. The analysis results of Cd and Zn in certified reference materials and two soil samples are consistent with the certified standard and verified values obtained via inductively coupled plasma optical emission spectroscopy. MF-SCGD is a promising technique with a compact instrument, low cost, low power consumption, and high discharge stability.