Development and Applied Research on Elemental Detection of Microwave Plasma Torch Time-of-flight Mass Spectrometer

Microwave plasma torch (MPT) has the advantages of low power consumption, convenient operation, simple structure, etc. It can be used with mass spectrometer for rapid analysis of elements. Inductively coupled plasma mass spectrometer (ICP-MS) has many advantages, such as high sensitivity and wide range of analyzed elements, but its high gas consumption and power consumption of ion source make the detection and analysis cost high. In order to effectively reduce the cost of mass spectrometry for the detection and analysis of alkali metal elements, this study reported a self-made low power-consuming microwave plasma torch time-of-flight mass spectrometer (MPT-TOF MS), including a three-cone system consisting of an ion source, a sampling cone, an interception cone, a super-interceptor cone, an ion transport lens set, a time-of-flight mass analyzer, a sample injection device, and a data acquisition system. The effects of five experimental factors, namely, maintenance gas flow rate, carrier gas flow rate, super-interception cone voltage, MPT torch flame position and microwave power, on the detection of alkali metal elements were investigated. The performance of the instrument was systematically investigated, covering the linear range, mass resolution, and isotopic accuracy of measurement. The results showed that the MPT-TOF MS has the advantages of low gas consumption (800 mL/min for argon maintenance gas, 400 mL/min for argon carrier gas, and 2 000 mL/min for nitrogen drying gas), low power consumption of the ion source (100 W), and long-time stable operation when working, and the linear range of the measurement of this device covers five orders of magnitude with high mass resolution. The detection limits of lithium, sodium, potassium, rubidium and cesium are 0.49, 3.05, 1.31, 0.74, 0.34 μg/L, respectively, which are better than the results of ICP-MS. The instrument was used for the rapid detection of lithium, sodium, potassium, rubidium and cesium alkali metal elements in the salt lake. Our study showed that the MPT-TOF-MS instrument can be used as an alternative to the elemental detection of ICP-MS, and can be further developed into an on-line analytical method.