Detection of trace heavy metals using atmospheric pressure glow discharge by optical emission spectra

In this Letter, atmospheric pressure glow discharge based on a small discharge gap is excited by sine AC voltage in air on purpose of detecting trace heavy metal elements in solid samples, which makes the detection limits of trace heavy metal elements reach tens μg/kg. The waveforms of voltage and discharge current, discharge images, plasma gas temperature, and optical emission spectra are obtained to discuss the feasibility of atmospheric pressure glow discharge on detection of trace heavy metals. The formation mechanism of optical emission spectra and the strong emission intensity of heavy metal elements show that energetic electrons and excited metal atoms are easily generated by atmospheric pressure glow discharge. The effects of applied voltage and discharge gap on atmospheric pressure glow discharge are discussed to acquire the optimal experimental conditions. And a smaller discharge gap and applied voltage can restrain the transition from glow discharge to arc discharge. Besides, the limits of detections of Cu and Cd are about 0.0241 and 0.0318 μg/g, respectively, by using atmospheric pressure glow discharge with an applied voltage of 3.8 kV, discharge gap of 3.5 mm, and driving frequency of 10 kHz.