Application Of DSN/LA-ICP-MS In The Determination Of Geological Samples

During the last decades inductively coupled plasma-mass spectrometry(ICP-MS) has been developed into an accurate and sensitive technique for multi-element determinations in a range of sample matrices.Compared with AFS,AAS and ICP-AES,ICP-MS offers better sensitivity and excellent accuracy with multi-element and isotope ratio measurement capabilities.However,the low abundance of trace elements makes the direct determination of silver in geological samples very challenging.Most methods require separation and pre-concentration of trace elements from complex matrices.Membrane desolvation system(DSN) is very effective to increases sensitivity and reduces the oxide and hydroxide interferences by removing water vapor.A method for direct determination of Ag by DSN-ICP-MS in geological samples has been developed.Laser ablation inductively coupled plasma-mass spectrometry(LA-ICP-MS)is an accurate and precise in situ and real time technique for trace element analysis of a wide variety of solid samples.It has becomes a powerful method,providing age and trace element data comparable to those of SIMS in both accurary and precision but with significantly high throughputs.U-Pb dating and trace elements of zircon megacrysts(1-10Ma) from three different places were studied in this work.Zircon standards 91500,GJ-1,SK10-2 and zircon megacrysts were detemined by LA-ICP-MS at a spot size of 44μm and 5ml/min N₂ adding.The results of zircon standards are agree with the reference valus and published values.The main results were summarized as following:1.Determination of Ag in geological samples by DSN-ICP-MS.1) Compared with the results obtained by using conventional ICP-MS,the signals intensity by DSN-ICP-MS were improved the oxide and hydroxide ratios were found to be reduced remarkably.The significant reduced oxide and hydroxide interferences should be attributed to the elimination of water vapor in sample aerosol.2) Increasing nitrogen addition leads to decrease in oxide and hydroxide ratios and increase in signal intensity.The removal of oxygen through NO formation was advocated as the dominant reason for the reduction of the oxide and hydroxide ratio.3) The determined concentration values of Ag by conventional ICP-MS are much higher than those obtained by membrane desolvation-ICP-MS.Most of the results obtained by menbrane desolvation ICP-MS are in good agreement with the reference values.This indicates that the equivalent concentrations of Ag caused by oxide and hydroxide interferences of Zr are far more than the actual concentration of Ag in geological samples.2.U-Pb dating and trace elements analysed of zircon megacrysts by LA-ICP-MS.1) To addition of 5ml/min nitrogen to the central channel gas in LA-ICP-MS increases the sensitivity for most of the 65 investigated elements by a factor of 1.5-2.5.2) Zircon standard 91500 was used as an external satandard for correcting mass discrimination and isotope fractionation for U-Pb dating,which was analyzed twice every 5 analyses of zircon samples.Zircon standards GJ-1,SK10-2 and zircon megacrysts were calculated by 91500.The results of GJ-1 and SK10-2 are agree with the reference valus or published values.3) The USGS glasses BCR-2G and BIR-1G were used as multi-calibration standards for external calibration of trace elements.4) U-Pb dating and trace elements of zircon megacrysts(1-10Ma) from three different places were analysed by the founded method,and got the satisfying results.