Direct Mass Spectrometric Analysis of Zinc and Cadmium in Water by Microwave Plasma Torch Coupled with a Linear Ion Trap Mass Spectrometer

Abstract

Microwave plasma torch (MPT) is a simple and low power-consumption ambient ion source. When MPT Mass spectrometry is applied in the detection of some metal elements, the metallic ions exhibit some novel features which are different with traditional ICP Mass spectrometry and may be helpful for the metal element analysis. Zinc and cadmium both are important transition metals with wide applications in modern industry. Here, we presented the research results about the MPT mass spectra of zinc and cadmium elements by a linear ion trap mass spectrometer (LTQ) both in positive and negative mode. Without any sample pretreatment, the aqueous samples were pneumatically nebulized and generated the aerosols. The dried aerosols were introduced into the plasma through the central tube of the MPT to generate the complex metallic ions. For the positive composite ions of zinc and cadmium, the general forms are the hybrid of M(NO 3)•nOH•mH 2 O, thus the MPT mass spectra are extremely complicated and unsuitable for the quantitative monitoring. However, the MPT negative ionic of zinc and cadmium are quite regular in the forms of M(NO 3). We also showed the limit of detection (LOD) for zinc and cadmium in negative mode can achieve at the level of 10μg/L (ppb). Therefore, the negative mode MPT mass spectrometry can be used as one of alternative supplements of ICP-MS applied in on-line monitoring of zinc and cadmium metal ions in water at trace levels, which will be promising in the field analysis of metal elements and the rapid water quality inspection.

Spray-inlet microwave plasma torch ionization tandem mass spectrometry for the direct detection of drug samples in liquid solutions

“…Moreover, these methods have been a breakthrough in the application of MS to high‐throughput analyses where the samples are placed directly between the ambient environment and the vacuum inside the mass spectrometer so that the state of the sample can be ignored . Depending on the ionization/post‐ionization methods, ambient techniques can be divided into the following three classes: (1) interaction with spray‐droplets, including desorption electrospray ionization (DESI) and probe electrospray ionization (PESI); (2) multimodal ionization containing both electrospray and plasma (where the interaction with the plasma stream is generated by an electric discharge), including direct analysis in real time (DART), microwave plasma torch (MPT), and low temperature plasma (LTP) analysis methods; and (3) ionization/desorption with radiation, including laser desorption electrospray ionization (LDESI) . These ambient ionization sources have been used to analyze a wide variety of compounds, ranging from small molecules to biomacromolecules, including nondestructive, high‐throughput, and reaction‐monitoring analyses .…”

“…As a novel high‐frequency plasma generator at atmosphere pressure, the MPT ionization source was developed in 1985 at Jilin University of China, and substantial improvements were subsequently made at Indiana University . The traditional applications of the MPT were mainly focused on optical spectroscopy in the excitation source to analyze metallic and nonmetallic elements . Recently, the MPT has begun to be used as an ion source for ambient mass spectrometry.…”

The Study of Titanium and Zirconium Ions in Water by MPT-LTQ Mass Spectrometry in Negative Mode

“…ICP-MS is a quite sensitive elemental analysis method and can determine the contents of titanium and zirconium. Nevertheless, in the current field analytical sense, ICP-MS is limited due to the general essential tedious chemical pretreatment, expensive and cumbersome equipment [ 17 , 18 , 19 ]. Microwave plasma torch (MPT)-mass spectrometry is one of the recently developed ambient mass spectrometric techniques with numerous merits.…”

“…The plasma technique possesses strong excitation ability and good universality, hence MPT has been used widely as a powerful light source in spectrometric instruments [ 21 , 22 , 23 , 24 , 25 , 26 ], and even then been applied in the direct analysis of solid samples [ 27 ]. Our previous studies have showed that the MPT, as an ambient ion source, coupled with a linear ion trap mass spectrometer, can be a potential analytical tool in various fields, especially in the analysis of metal elements [ 17 , 18 , 19 , 20 , 28 ]. By adopting a desolvation unit, and injecting aqueous samples through the central-tube of the MPT unit, MPT-mass spectrometry has been applied to detect directly and sensitively many kinds of metal elements in water without tedious sample pretreatment procedures [ 29 , 30 , 31 ].…”

“…Meanwhile, the positive and negative modes of the LTQ (linear ion trap) mass spectrometer can both couple with the MPT source to perform the detection of metal elements. However, for transition metal elements, the negative mode usually exhibits lower background and simpler spectral structure [ 28 ] due to the fact that less complex metallic anions (containing several OH and H 2 O groups) produced in the MPT plasma are superposed with their corresponding isotopes, such as in the typical examples, zinc and cadmium [ 17 ]. Moreover, some transition metal elements, including titanium, zirconium and noble metals, have no obvious signal in positive mode.…”