Signal Enhancement Of Active-matrix In LA-ICP-MS And Its Applications

Laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) known as the most powerful in situ analysis technology, has been widely used in various fields, such as geoscience. Recently, the precise and accurate quantitative analysis of trace element and isotope, especially simultaneous determination of trace element with isotopes or multi-isotopes, in samples of complex matrix, low concentration and high spatial resolution requires higher sensitivity and lower interference level. Introduction of active matrix, such as nitrogen, water vapor and organic solvents etc., to improve the properties of plasma is an effective method to enhance sensitivity and suppress interferences, which has been extensively researched in SN-ICP-MS, but rarely studied in LA-ICP-MS. In this thesis, we investigated the effects of the addition of water and/or ethanol vapor to the central gas flow (Ar+He) of an Ar plasma in combination with a shielded torch on the signal intensity, polyatomic ion level, and discussed the possible mechanisms of enhancement effect, basic on systematically references research. We also estimated new analysis strategy with low DL, high precision and accuracy, which has been successful utilized in U-Pb dating of zircon. This work was carried out from the following three aspects:1、In this section, we focused on discussing the changes of the general physical and chemical properties of traditional Ar plasma due to introduction of nitrogen and organic solvents, and their applications in signal enhancement and mass interferences suppression. We also discussed the possible mechanisms of mixed gas plasma in terms of general physical and chemical property changes during ICP analysis.2、We investigated the effects of the addition of water and/or ethanol vapor to the central gas flow (Ar+He) of an Ar plasma in combination with a shielded torch on the signal intensity, polyatomic ion level, and discussed the possible mechanisms of enhancement effect in193nm ArF LA-ICP-MS setup. The results show that:(1) water and/or ethanol vapor were added directly into dry aerosols with a custom made introduction system providing long-term stability.(2) the effect of the shielded torch on the LA-ICP-MS sensitivity is minimal for dry plasma conditions but becomes significant in the presence of water and/or1-4%(v/v) ethanol vapor. For most of the60investigated elements reported in this study, the addition of small amounts of water and/or1-4%(v/v) ethanol vapor into the carrier gas increases the sensitivity by a factor of2.5-3.0or1.2-1.5with or without the shielded torch, respectively. The suppression of the ion kinetic energy distribution by the shield in the presence of water and/or1-4%ethanol vapor may account for the increase in sensitivity.(3) with the shielded torch, the oxide ratio increases from0.47%in dry plasma to6.41%in water plasma and decreases to0.81%in4%ethanol plasma. Hydride formation increases by a factor of27in the presence of4%ethanol vapor relative to dry plasma. The yield of doubly charged ions decreases from1.2%in dry plasma to0.8%and0.7%in water and4%ethanol plasmas with the shielded torch, respectively.(4) relative to the spatial profiles of the ion distributions in dry plasma, the addition of water and/or2%(v/v) ethanol vapor in combination with a shielded torch shows several effects-significantly narrow axial profiles, the shift of maximum ion density zone away from the load coil and more uniform ion distributions for elements with different physical and chemical properties.(5) The combination of changes in ICP geometry, enhanced vaporization, atomization and ionization of analyte, and efficient ion transmission with a shielded torch contributes to the sensitivity enhancement observed in this study.3、We used the technology of water and/or ethanol vapor in combination with shielded torch to estimate a new analysis strategy with low DL, high precision and accuracy which has been successful utilized in high spatial resolution of U-Pb dating of zircon. The experiment results show that:(1) By introducing water/ethanol vapor in combination with shielded torch, we could precise and accurate detemined the U-Pb age of zircon standards of91500and GJ-1. The detemined206Pb/238U age of91500and GJ-1in this study is1064±10Ma (2a, MSWD=0.30, n=19) and600.1±4.7Ma (2σ, MSWD=0.0053, n=19) respectively, which agree well with ID-TIMS analysis ages.(2) Under each experimental condition, the precision (2σ) improved gradually with spot size and laser frequency increasing, and was significantly better in2%ethanol plasma than in dry plasma. In additional, the RSDs and accuracy (REs) reduced slowly with spot size increasing, but the trend was not obviously. Laser frequency and plasma conditions had litter effect on RSDs and REs. Thus, the RSDs and REs were identically at1%RSDs and REs at each experimental conditions.(3) The effect of spot size, laser frequency and plasma conditions on precision and accuracy of U-Pb age depended on analysis sensitivity.