Applied Research On High Resolution Inductively Coupled Plasma Mass Spectrometry For Analysis Of High Purity Metal Samples

With the development of high purity metal applied to high-tech fields,it is requested for higher purity.Due to the severe effect of trace elements on the physical and mechanical properties of the high pruity metal,it is an urgent task for high purity metal to contral critically and analyse accurately the concentration of these elements.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 other methods,ICP-MS offers better sensitivity and excellent accuracy with multi-element and isotope ratio measurement capabilities, and it is used widely in the measurement of high purity material.The interference of overlapped spectrums caused by the solvent and plenty of metal substances is still a serious problem occurring in ICP-MS.High resolution inductively coupled plasma mass spectrometry(HR-ICP-MS) can effectively remove a lot of interferences caused by plasma-mass, water and matrix element.The theoretical foundation of HR-ICP-MS is expounded systematically and the HR-ICP-MS applied to the measurement of high purity metal in the following ways is discussed.The studies in the thesis are summarized as follows:(1) The determination of 13 trace impurities including Na,Mg, Ca,Cr,Mn,Fe,Co,Ni,Cu,Mo,Cd,Sb and Pb in high purity zinc oxide by HR-ICP-MS was described.The spectral interferences in determination of trace elements in high purity zinc oxide and the probable eliminating methods were investigated.Through apropriate settings of the operational parameters and correcting interferences,the individual elements interfered could be determianed.To overcome some potentially problematic spectral interference,measurements were acquired in both medium and high resolution modes.The matrix effects due to the presence of excess HCl and zinc were evaluated.The optimum conditions for the determination was tested and discussed.The standard addition method was employed for quantitative analysis,13 elements in high purity zinc oxide powders could be determined directly, and the results were in good agreement with the referred values.The detection limits range from 0.02μg/g to 6μg/g depending on the elements,the relative standard deviation(RSD) was less than 4.7%and the recoveries were between 90%¹10%.Another approach for checking the trueness of the method was to compare the results obtained by this method characterizing the high purity zinc oxide with those obtained by application of inductively coupled plasma atomic emission spectrometry(ICP-AES) and atomic absorbtion spectrometry(AAS). The result showed that HR-ICP-MS was significantly lower than the detection limit of ICP-AES and AAS about 1² orders of magnitude.(2) Without matrix separation but(NH₄)₂SO₄ and H₂SO₄ dissolution, the interferences and matrix effects in ICP-MS for high purity titanium dioxide were serious.An analytical method using HR-ICP-MS for rapid simultaneous determination of Be,Na,Mg,Al,V,Cr,Mn,Fe,Co,Ni, Cu,Zn,Ga,Ge,As,Mo,Cd,Sn,Sb,Ba,Ce,Nd,Sm,Pt,Pb and Bi in high purity titanium dioxide was described.Samples were decomposed by(NH₄)₂SO₄ and H₂SO₄,the solution was analyzed by HR-ICP-MS. Most of the spectral interferences could be avoided by measuring in the high resolution mode.Correction for matrix effects was tried using internal standard elements.The standard addition method was employed for quantitative analysis.The optimum conditions for the determination was tested and discussed.The detection limits was 0.004μg/g⁰.63μg/g,the recovery ratio was 87.6%¹06.4%,and the RSD was less than 3.5%,most of the trace elements in high purity titanium dioxide were of the same higher sensitivity by HR-ICP-MS compared to that by ICP-MS.(3) The trace elements in high purity gallium have serious effects on their physical functions.In this study,an analytical method using HR-ICP-MS for rapid simultaneous determination of Be,Mg,Al,Si,Ti, V,Cr,Mn,Fe,Co,Ni,Cu,Zn,Ge,As,Mo,Ag,Cd,In,Sb,Ba,Pb and Bi elements in high purity gallium was described.The sample was dissolved in HNO₃ and HCl by microwave digestion then the above 23 elements in the solution was analyzed directly by HR-ICP-MS.Most of the spectral interferences could be avoided by measuring in the high resolution mode(HRM).The matrix effects due to the presence of excess HCl and Ga were evaluated.The optimum conditions for the determination was tested and discussed.The result showed that the correction for matrix effects was made using Sc,Rh and Ti as internal standards.The detection limits of the method was in the range of 0.001μg/L⁰.21μg/L,the relative standard deviation(RSD) was less than 3.3%and the recovery of the samples was in the range of 89.8% 111.6%.Research method could meet the analytic demand of high purity gallium between 99.99%(4N) and 99.99999%(7N).(4) An analytical method for rapid simultaneous determination of 24 elements(Be,Mg,Al,Ti,V,Cr,Mn,Fe,Ni,Cu,Zn,Ga,Ge,As,Se, Mo,Ag,Cd,Sn,Sb,Ba,Pt,Au and Pb) in high purity cobalt by high resolution inductively coupled plasma mass spectrometry(HR-ICP-MS) with microwave was described.The conditions of microwave digestion, the matrix effect and spectral interferences were investigated,and the parameters of the ICP inoization source,mass spectrometry and microwave digestion were optimized.Sample digestions were performed in closed microwave vessels using HNO₃ and HCl.The matrix effects due to the presence of excess HCl and Co were evaluated.The usefulness of high mass resolution for overcoming some spectral interference was demonstrated.The trend of RSD of the correction results corresponding to the isotopes by the multi-internal-standard(Sc, Y,Rh,In and Bi) correction was illustrated.Research results showed that it was better to use the internal standard of which the mass was near to that of the analytical elements,so multi-internal-standard correction was recommended for multi-element analysis in high purity cobalt.The result showed that the detection limit range of the method was within the scope of 0.016μg/g¹.50μg/g for 24 elements.The precision and recovery tests were made and the results obtained were as follows:the recoveries in the range of 92.2% 111.2%and the RSD was less than 3.6%.(5) There are difficulties in determining the hard-to-ionize elements, such as Be,Zn,As,Se,Sb and Hg by ICP-MS.Although most elements in the periodic table are ionized with an efficiency of more than 90%in ICP,hard-to-ionize elements are ionized with considerably lower efficiency,resulting in relatively poor analytical sensitivity.In this paper, the matrix effects arising from oxalic acid,lactic acid,tartaric acid and citric acid in ICP-MS has been investigated for the first time.It has been proved that the sensitivity of analytes can be significantly enhanced by adding small amounts of organic acid compounds with adjusted nebulizer flow-rate gas,especially for the elements with ionization potential between 9 and 11eV.The tartaric acid has higher enhancement effect on the signal intensity of the hard-to-ionize elements than that of oxalic acid,lactic acid and citric acid.The mechanism of the enhancement was investigated.The tartaric acid can be used to compensate the signal depression caused by inorganic matrix and to improve the detection limits about five to twenty-two times,for the hard-to-ionize elements(Be,Zn,As,Se,Sb and Hg) in ICP-MS determination.The method has been used to determine Be,Zn,As,Se, Sb and Hg in water standard reference materials(SRM).The analytical results are agreement with the certified values.The RSD was in the range of 1.40%-4.42%.