A microwave plasma torch quadrupole mass spectrometer for monitoring trace levels of lead and cadmium in water

Abstract

RATIONALE: The microwave plasma torch (MPT) is a low power-consumption and easily operated plasma generator. As an ambient ion source, the MPT can be coupled with various mass spectrometers and applied in real-time analysis of metal elements in water for the demands of environmental control and water quality inspection. METHODS: We constructed a quadrupolemass spectrometer with an MPT as the ion source to detect directly trace levels of lead and cadmiumin water. Without any pretreatments, water sampleswere first pneumatically nebulized with a desolvation unit, then flowed through the central tube of the MPT and finally entered the plasma. After that, themetal ions produced were introduced into the mass spectrometer to be analyzed via an atmospheric inlet of a stainless steel capillary tube. RESULTS: The MPT mass spectra of lead and cadmium ions were characterized with clear unit isotopic resolution. The sensitivity reached levels of 20 ng/L for lead and 72.7 ng/L for cadmium in water, respectively. The linear response range covered at least 2 orders of magnitude. Moreover, a single aqueous sample could be completely analyzed within 3 minutes, providing reasonably relative standard deviation values. CONCLUSIONS: Our results demonstrated that this MPT mass spectrometer is a useful tool for the monitoring of lead and cadmium ions in water, which makes it a potential alternative to ICP-MS, to be used in the fields of environmental control and water quality and foodstuff safety inspection.