2005 PerkinElmer The Study of Mass Spectrum Interferences in the Determination of High Purity 1 Rare Earth Products by using Inductively Coupled Plasm

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1 2005 ( ) PerkinElmer ICP-OES ICP-MS

2 2005 PerkinElmer The Study of Mass Spectrum Interferences in the Determination of High Purity 1 Rare Earth Products by using Inductively Coupled Plasma Mass Spectrometry Direct Determination of Rare Earth Impurities in High Purity Ytterbium Oxide 15 by Inductively Coupled Plasma Mass Spectrometry 21 ICP-MS 30 -ICP-OES 35 ICP-AES 38 ICP-OES ICP-AES ICP-OES 60 - Si Fe Na ICP-OES 15 75

3 PerkinElmer Environmental Applications o f the ELAN DRC-e ICP-MS 82 Interference Removal and Analysis of Environmental Waters Using the ELAN 86 DRC-e ICP-MS Bromine Speciation by HPLC/ICP-MS 96 Simultaneous Arsenic and Chromium Speciation by HPLC/ICP-MS in 100 Environmental Waters Radionuclide and trace element contamination around Kolaghat Thermal 103 Power Station, West Bengal Environmental implications Using Dynamic Reaction Cell ICP-MS Technology to Determine the Full Suite 111 of Elements in Rainwater Samples Experience Using Filter Paper Techniques for Whole Blood Lead Screening in 118 a Large Pediatric Population As(III) and Sb(III) Uptake by GlpF and Efflux by ArsB in Escherichia coli 126 Continuous Flow Hydride Generation Using the Optima ICP 134 Trace Level Analysis of Calcium, Magnesium, Potassium and Sodium Using 138 the Optima ICP Determination of Impurities in High-purity Gold 142 Determination of Impurities in Purified Terephthalic Acid (PTA) 145 Correction for non-spectroscopic matrix effects in inductively coupled 148 plasma-atomic emission spectroscopy by internal standardization using spectral lines of the same analyte A Drift Correction Procedure 159 Single-Element Solution Comparisons with a High-Performance Inductively 166 Coupled Plasma Optical Emission Spectrometric Method An ICP-OES Method with 0.2% Expanded Uncertainties for the 175 Characterization of LiAlO 2 Natural Remediation of Contaminants along the Forgotten River Stretch of the 183

4 Rio Grande Cardiovascular effects of Tacca integrifolia Ker-Gawl extract in rats 190 Determination of organo-zinc based fungicides in timber treatments employing 199 gas chromatographic analysis with mass selective detection and/or inductively coupled plasma atomic emission spectroscopy Structure and magnetic properties of rf thermally plasma synthesized Mn and 207 Mn Zn ferrite nanoparticles Field scale study results for the beneficial use of coal ash as fill material in 210 saturated conditions, varra coal ash burial project, weld county, colorado Digestion and Characterization of Ceramic Materials and Noble Metals 214

5 2005 PerkinElmer ICP-OES ICP-MS The Study of Mass Spectrum Interferences in the Determination of High Purity Rare Earth Products by using Inductively Coupled Plasma Mass Spectrometry Xinquan Zhang*, Jinlei Liu, Yonglin Liu, Xiang Li, Yong Yi, Yumei Jiang, Yaqin Su Jiangxi Institute of Analyzing and Testing, Nanchang , China Abstract This paper reported the mass spectrum interfering problems during analytical procedures with trace rare earth elements (REES) as impurities in fifteen high purity rare earth products by using ELAN 9000 inductively coupled plasma mass spectrometry (ICP-MS) technique. The interfering effects caused by interfering species originated from background mass spectrum, isobaric overlaps, mass spectrum overlaps and matrix-induced polyatomic ions that interfer the quantification of the specified analytes were evaluated deeply. The relationship between polyatomic ions originated from matrix-induced and the instrumental conditions was also investigated. Through quantitative analysis, the appearance concentrations of polyatomic ions arose from matrix-induced and matrix mass spectrum overlaps were presented. According to the mass spectrum interferences, the resolving methods of correction interferences were put forward. The limit of quanlitation (LOQ) for trace of REEs impurities and acquiring purity under direct determination of fifteen high purity rare earth products were also investigated. Keywords: Inductively coupled plasma mass spectrometry; High purity rare earth products; mass spectrum interferences 1. Introduction With the development of widely applications of high purity rare earth products in many fields, such as industry, nuclear technique, aviation and spaceflight, the demand for purity analysis of rare earth products with precision and accuracy is increasing. In general, several analytical techniques such as X-ray fluorescene (XRF), neutron activation analysis (NAA) and inductively coupled plasma emission spectrometry (ICP-AES)[1-3] have been employed for the quantification of REEs as impurities in relative lower purity rare earth products. However, these analytical techniques, are only effective for the lower purity of rare earth products but not adequate for rare earth products with high purity (99.99%~99.999%) in terms of sensitivity, complex spectral interference [4-5]. After Houk et al.[6] first published their methodology by using inductively coupled plasma (ICP) as an ion soure combined with mass spectrometer (MS), twenty five years have passed. Today, This analytical technique regarded as a principal measure is widely applied in the analytical fields such as high purity materials, circumstance, metallurgy, biochemistry et al. Due to its performance with high sensitivity, low detection limits, determination capability of multielements at ultra-trace level at the same time and wide dynamic range, it also becomes the major analytical method used for the determination of ultra-trace REEs as impurities in high purity rare earth products day by day[7-14]. Although ICP-MS technique possesses protrusive advantages compared with other atomic 1

6 2005 PerkinElmer ICP-OES ICP-MS spectrometric techniques, but some mass spectrum interferences produced from plasma- and matrix solvent-induced polyatomic ions as background spectrum, isobaric overlaps, matrix-induced polyatomic ions and matrix-induced spectrum overlaps that affect the neighbouring two mass numbers (M-1, M+1) analytes, limit the applications in the analytical field of high purity materials in certainly degree. Zhang et al.[11,12] utilized ICP-MS technique and reported the determination of the ultra-trace REEs as impurities in high purity CeO 2 and Sm. Through the method of matrix-match, the mass spectrum interferences generated from matrix-induced polyatomic ions and matrix-induced spectrum overlaps were overcame partly, then the determination of the two kinds of high purity rare earth products was enhanced to 99.9%~99.99%. Pedreira et al. [13, 14] accomplished the determination of rare earth analytes as impurities in high purity La 2 O 3 and Pr 6 O 11 with ICP-MS combined with high-performance liquid chromatography (HPLC) technique after matrix elements as La and Pr had been separated respectively by HPLC. Some papers evaluated the mass spectrum interferences associated with the matrix, such as polyatomic ions (MO +, MOH + ) generated in the plasma [15, 16]. But few of papers maked a systematic and quantitative investigation utilized ICP-MS technique in the determination of fifteen rare earth products during analytical procedures about a series of mass spectrum interference generated from background spectrum, isobaric overlaps, 2 matrix-induced polyatomic ions and matrix-induced mass spectrum overlaps, which interfere in the quantification of the REEs of interest with precision and accuracy. This is the exactly purpose that we will be discuss in this paper. 2. Experimental 2.1 Instrument A Perkin-Elmer Sciex ELAN 9000 ICP-MS equipped with a integrated peristaltic pump and a cross flow nebulizer combined with a scott spray chamber that was made from Ryton TM material was used. The instrumental conditions are summarized in Table 1. Before the analytical procedure, the X, Y positions of torch, the nebulizer gas flow and the lens voltage were optimized by using a quality concentration standard solution of 10µgL -1 Mg, Ce, Rh, In, Pb, Ba. After those optimization was accomplished, then optimized Auto Lens TM voltage by using another quality concentration standard solution of 10µgL -1 Be, Co, In. Finally, selected the Daily Performance. wrk from ELAN software to check the instrumental performance, confirmed that the sensitivity of spiked elements as In, Mg, Pb with quality concentration of 10µgL -1 amounted to about more than counts per second (cps), cps and Pb for cps respectively, percentage 140 Ce 16 O + / 140 Ce + and Ba 2+ /Ba + ratios about less than 3.0%, and the background of mass number 220 was also less than 10 cps. Table 1 Operating condition of ELAN 9000 ICP-MS RF Power (w) 1000 Resolution (amu) 0.70 Nebulizer Gas Flow (Lmin -1 ) 0.90 Detector dual Lens voltage (v) 6.0 Speed of Peristaltic Pump (rpm) 26 Analog Stage Voltage (v) Sweeps/Reading 3 Pulse Stage Voltage (v) 1000 Replicates 3 Discriminator threshold (v) 70 Scan Mode Peak hopping or scanning Ac rod offset (v) Reagents The superpure HNO 3 used in this work was acquired by the analytical-reagent grade HNO 3 under sub-boiling condition. H 2 O 2 was the AR grade. Sample solutions were prepared with purified water from a TYUV05 water unit with the resistivity being more than 18.3M cm ( Tao Yuan

7 2005 PerkinElmer ICP-OES ICP-MS Company, Nanchang, China). 2.3 Samples and sample preparation High purity samples with purity more than about %: La 2 O 3, Sm 2 O 3, Eu 2 O 3, Ho 2 O 3, Er 2 O 3, Tm 2 O 3, Yb 2 O 3, Lu 2 O 3 and Y 2 O 3 were acquired from Hunan Institute of Rare Earth Material (Hunan, China). High purity samples with purity more than about 99.99%: CeO 2, Pr 6 O 11, Nd 2 O 3, Gd 2 O 3, Tb 4 O 7 and Dy 2 O 3, were purchased from Johnson Matthey Company (Warel Hill, USA). 0.1g of the fifteen rare earth samples was accurately and respectively weighted into a 100mL beaker, and decomposed with ultrapure water 10mL and superpure HNO 3 2mL on a hot plate which heated at about 80 (3mL H 2 O 2 was added in addition when CeO 2 was decomposed). After the dissolving solution cooled, transferred it into a 100mL volumetric flask individually and finally diluted with ultrapure water, so the quality concentrations of each of the fifteen rare earth products were 1.0gL -1. After those dissolving solutions regarded as stock solution were accomplished with preparation procedures, then diluted them into 50mL volumetric flask with ultrapure water and added 0.5mL superpure HNO 3 in addition. Finally, The quality concentrations of the matrix of fifteen rare earth samples in the solutions were 1.0 gml -1 and 500µgmL -1 respectively. The 500 gml -1 solutions were spiked with In as internal standard with the quality concentration of 10 gl -1. Prepared blank solution at the same time. All of the beakers and volumetric flasks used in this work were carefully washed with 10% HNO 3 and then washed repeatedly with ultrapure water in order to reduce blank value. Analyte 2.4 ICP-MS determination The ELAN software provides two different modes for acquiring mass spectral data of interest during a analytical procedure. These options are the modes of peak hopping and scanning. In the solutions which fifteen rare earth matrix concentration were 500 gml -1, the appearance concentrations of the interfering ions generated from matrix-induced polyatomic ions and matrix-induced mass spectrum overlaps were obtained quantitatively by the option of selecting peak hopping mode and setting the MCA channels value to one. Otherwise, in the solutions which fifteen rare earth matrix concentrations were 1.0 gml -1, the mass spectrum were acquired individually through the option of selecting scanning mode and setting the MCA channels value to eleven. 3. Results and discussion 3.1 Plasma and matrix solvent induced polyatomic ions The presence of atmospheric gases or the argon carrier is source of potential interfering ions as the result of reaction with other analyte or matrix components [17]. These interfering ions occur as polyatomic, molecular ions. In addition, the solvent or acid in which the sample is dissolved can also be another source of interfering polyatomic ions. Chlorine from hydrochloric or perchloric acid and sulfur from sulfuric acid all form polyatomic ions with argon and other plasma gases. For organic solvents, carbon and oxygen can form polyatomic ions. Interfering ions of various types listed above can affect the determination of some analytes, These are illustrated in Talbe 2. Table 2 Plasma-induced and matrix solvent-induced polyatomic ions interferences Abundance of Isotope 28 Si S K Ca Ca Ti Interfering Ion Analyte Abundance of Isotope 12 C 16 O + 51 V O Fe ArH + 64 Zn Ar + 75 As C 16 O Se S 16 O + Interfering Ion 35 C 16 O + 40 Ar 16 O + 32 S 16 O + 2, 32 S Ar 35 Cl + 40 Ar + 2 3

8 2005 PerkinElmer ICP-OES ICP-MS Taking an analytical procedure of mass spectral scanning with blank solution, the mass spectrum as Figure 1 was obtained. It is evident from Figure 1 that those interfering ions listed in Table 2 mainly affect the determination of the analytes which mass numbers are less than 80. In the periodic table, the mass range of 14 REEs (La~Lu) varies from 138 to 176 and the lowest mass of rare earth products is 89 of yttrium, so there has no influence of spectral overlap interferences that can affect the determination of REEs as impurities in high purity products because the mass of those polyatomic ions are less than 80. It can be seen from Figure 2 of the mass spectrum of Y 2 O 3 with a solution of 1.0 gml -1. Fig. 1. Background mass spectrum with blank solution Fig. 2. Y 2 O 3 mass spectrum with concentration of 1.0µgmL Isobaric overlaps interference Since most elements have more than one naturally occurring isotope, it is possible for the mass spectrum of an isotope of one element to directly overlap that of an isotope of another element. These interferences are termed isobaric overlaps. It means that some elements can not be determinate with accuracy due to the isobaric overlaps interferences. Most of the 15 REEs have more than one naturally occurring isotope except several REEs have only one isotope, such as 89 Y, 141 Pr, 159 Tb, 165 Ho and 169 Tm. So there have some overlap interferences that affect the results of the determination of trace amount of REEs as impurities in high purity rare earth products during ICP-MS analytical procedures. Table 3 illustrates the isobaric between some REEs. Table 3 Isobaric of rare earth elements* Isobaric Analyte Isobaric Analyte 138 La(0.09), 138 Ce(0.26) 156 Gd(20.6), 156 Dy(0.06) 142 Ce(11.1), 142 Nd(27.1) 158 Gd(24.7), 158 Dy(0.1) 144 Nd(23.9), 144 Sm(3.1) 160 Gd(21.7), 160 Dy(2.3) 148 Sm(11.2), 148 Nd(5.7) 162 Dy(25.5), 160 Er(0.14) 150 Nd(5.6), 150 Sm(7.4) 164 Dy(28.2), 164 Er(1.6) 153 (26.7), 152 Gd(0.2) 168 Er(27.0) 168 Yb(0.14) 154 Sm(22.8), 154 Gd(2.2) 170 Er(15.0), 170 Yb(3.0) 176 Yb(12.7), 176 Lu(2.6) *: (x), x refers to abundance value This problem can be overcomed by selecting of isotopes carefully when developing analytical methods. For example, in the determination of trace of amount of REEs as impurities in high purity La 2 O 3 with purity varying from % to % [18], it had isobaric overlap interferences that affected the determination of the analyte 4

9 2005 PerkinElmer ICP-OES ICP-MS of Ce. The reason for this was that overlap interferences existed between 136 Ce(0.19) and 136 Xe(8.9), 138 Ce(0.26) and 138 La(0.09), 142 Ce (11.1) and 142 Nd(27.1). Otherwise, overlap interference occurred from matrix [ 139 La(99.9)]-induced affected the isotope as 140 Ce(88.5). Under the circumstance of not changing the instrumental resolution value, the concentrations of specified analytes of Ce and Nd were obtained by selecting isotopes as 142 Ce(11.1) and 143 Nd(12.2). After the concentration of isotope 143 Nd(12.2) was obtained, then the concentration of isotope 142 Ce(11.1) was also acquired by subtracting the contributing of 142 Nd(27.1) to the mass of 142, that was established a correction equation: C (142)Ce =C 142 -Abundance of 142 Nd/Abundance of 143 Nd C (143)Nd. Where C 142 was the total concentration at mass 142. Mirror isobaric overlaps can be corrected through establishing elemental equations like this. The instrumental software provides some equations and automatically corrects for known isobaric overlaps when calculating analyte concentrations in samples. But we must make a concrete analysis according to concrete condition in order to acquire accurary results. 3.3 Matrix-induced polyatomic ions interferences Polyatomic ions, such as MO +, MOH and MO + 2 may also be generated by sample matrix combination with oxygen and hydrogen [15,16]. These interfering ions create extreme influence on the measurement of the trace amount of REEs as impurities in high purity rare earth products. In order to protect the ETP detector due to extremely higher sensitivity of ELAN 9000 ICP-MS, a series of mass spectrum of matrix and matrix-induced polyatomic ions were obtained respectively with using the solutions of fifteen rare earth products In order to distinguish accurately the forms of polyatomic ions came from matrix of high purity rare earth samples and mass spectral interfering degree, the which quality concentrations were 1.0 gml -1 and taking mass spectral scanning according to mass range individually. Figure 3 and figure 4 describe typically that matrix have generated polyatomic ions with oxygen or hydrogen and formed mass spectral interferences overlap the mass of analytes of interest, such as 163, 164, 165, 166, 167, 168, 169, 170, 171 from Sm-matrix and 170, 171, 172, 173, 174, 175 from Gd-matrix. Fig. 3. Sm 2 O 3 mass spectrum with concentration of 1.0µgmL -1 Fig. 4. Gd 2 O 3 mass spectrum with concentration of 1.0µgmL -1 high purity La 2 O 3 with quality concentration of 500 gml -1 solution was selected and then executed a mass spectral scanning procedure. The mass spectrum was acquired without selecting isotopes of 5

10 2005 PerkinElmer ICP-OES ICP-MS the matrix element as 138 La or 139 La and that is illustrated in Figure 5, It can be seen from figure 5 that there have many polyatomic ions generated from La matrix combination with oxygen and hydrogen present at mass 154, 155, 156, 157, 158 and 171, with corresponding in order, these polyatomic ions are 138 LaO +, 139 LaO +, 139 LaOH +, 139 LaOH + 2, 139 LaOH + 3 and 139 LaO + 2. I mass /I In /C (138)La or C (139)La 100% (1) I mass /I In (2) Where: I mass refers to the intensity of the specified mass I In refers to the intensity of the internal reference as In of cps (n=3) C (138)La refers to concentration of 138 La[500µgmL -1 Abundance(0.09%)=0. 45µgmL -1 ] C (139)La refers to concentration of 139 La[500µgmL -1 Abundance(99.9%)=49 9.5µgmL -1 ] 10 refers to concentration of internal reference as In, gl refers to coefficients for unit of gl -1 converts as gml -1 The producing ratios and appearance concentrations for interfering ions occurred from matrix-induced polyatomic ions are shown in Table 4. Fig. 5. La 2 O 3 mass spectrum with concentration of 500µgmL -1 The producing ratios and appearance concentrations of polyatomic ions were quantitative determinated with selecting peak hopping scan mode and calculated as following equations (1) and (2): Table 4 Producing ratios and appearance concentrations of polyatomic ions generated from matrix of La with concentration of 500µgmL -1 (n=3) Polyatomic ions Intensity (cps) Producing ratio (%) Appearance concentration ( gml -1 ) 138 LaO LaO LaOH LaOH LaOH LaO Table 4 shows that the producing ratios for interfering ions described as above vary from % to 2.42%, and appearance concentrations from µgmL -1 to 12.08µgmL -1, that is the overlap interfering concentrations amount to from 0.00xµgmL -1 to xxµgml -1. The interference of polyatomic ion as MO + is the most serious interference and that for MOH + is the second. The interfering degree of these polyatomic ions is in the order: MO + >MOH + >MOH + 2 >MOH + 3 >MO + 2. It needs to notice in this example that the matrix element La has another naturally occurring isotope as 138 La(0.09). It can also form polyatomic ions as same as that of isotope of 139 La(99.9). The mass spectrum of these interfering ions overlap that of mass of 154, 155, 156, 157, and 170 in order. Since the concentration of 6

11 2005 PerkinElmer ICP-OES ICP-MS 138 La(0.09) is only of 0.45µgmL -1, the concentration of 138 LaO + generated from 138 La(0.09) is about of 0.01µgmL -1 and that of 138 LaOH and 138 LaO + 2 formed by 138 La(0.09) are more lower than 0.01µgmL -1, so it can be neglected that interferences caused by these polyatomic ions as 138 LaOH and 138 LaO + 2 overlap the mass of 155, 156, 157 and 170. In the application of the analysis of fifteen high purity rare earth products using ICP-MS analytical technique, only four high purity products of Y, Ho, Tm and Lu could be directly determinate the trace of amount of REEs as impurities [10,19]. The reason for this was that it was difficult for accurate determination of some of the REEs as impurities in the eleven high purity products because of the interfering ions arose from matrix-induced polyatomic ions and else. The overlap interferences caused by matrix-induced polyatomic ions could be partly overcame by using the procedure of matrix-match [11,12], but this method could not solve completely the problem about mass spectral interferences occurring from matrix-induced polyatomic ions. Determination of trace amount of REEs in high purity rare earth products using ICP-MS after separation of matrix is another often taken measure for overcoming mass spectrum of overlap interferences generated from matrix-induced polyatomic ions. Li et al. [20] reported for the determination of trace of REEs in high purity CeO 2 by ICP-MS after separation by solvent extraction. After removal of the matrix by using 2-ethlhexyl hydrogen-2-ethylhexylphosphonate (EHEHP), the polyatomic interference in ICP-MS were negligible. 3.4 Matrix mass spectral overlap interferences In the determination of trace REEs as impurities in high purity rare earth products by using ICP-MS technique, there is another interference arose from matrix (assuming mass with M) mass spectrum overlap interferences that affect the accurate measurement of the neighbouring analytes with mass for M-1 and M+1. The appearance concentration of the neighbouring analytes relation to the matrix elements in 500µgmL -1 solutions of fifteen rare earth products were acquired quantitatively by using peak hopping scan mode and setting the instrumental resolution value to 0.7amu and the results are given in Table 5. The appearance concentrations were calculated as the same as part 3.3 of equation (2). Table 5 Appearance concentration (µgl -1 ) of mass M-1 and M+1 arose from matrix mass spectrum overlap interferences (n=3)* Matrix 139 La(99.9) Analyte (M-1) Appearance concentration ( gl -1 ) Analyte (M+1) Appearance concentration ( gl -1 ) 140 Ce(88.5) Ce(11.1) 142 Ce(11.1) 141 Pr(100) 142 Nd(27.1) 146 Nd(17.2) 139 La(99.9) Ce(88.5) Pr(100) Pr ** (100) 143 Nd(12.2) Ce(11.1), 142 Nd(27.1) Sm(15.0) Sm(15.0) 152 Sm(26.7) 154 Sm(22.8) 151 Eu(47.8) 153 Eu(52.2) 158 Gd(24.7) 160 Gd(21.7) 146 Nd(17.2) 151 Eu(47.8) Nd(5.6), 150 Sm(7.4) Eu ** (52.2) 155 Gd(14.9) 152 Sm ** (26.7), 152 Gd(0.2) 154 Sm(22.8), 154 Gd(2.2) 159 Tb ** (100) 161 Dy(18.9)

12 2005 PerkinElmer ICP-OES ICP-MS 159 Tb(100) 164 Dy(28.2) 158 Gd(24.7), 158 Dy(0.1) Gd(21.7), 160 Dy(2.3) Ho(100) Ho(100) 164 Dy(28.2), 164 Er(1.6) Er(33.4) Er(33.4) 165 Ho(100) Er(27.0) 170 Er(15.0) 169 Tm(100) 174 Yb(31.8) 175 Lu(97.4) 168 Er(27.0), 168 Yb(0.14) Yb(31.8) Tm ** (100) Yb(14.3) Er(15.0), 170 Yb(3.0) Lu ** (97.4) 3.86 Note: * : If the abundance of some isotopes belong to some matrix are less than the value of 10%, since the concentrations of these isotopes are less than 50µgmL -1, so the mass spectrum overlap interferences arose from matrix for the neighbouring analytes of mass as M-1 and M+1 can be neglect; **: some analytes suffer mass spectrum overlap interferences from the two isotopes belong to a matrix element, for example, 169 Tm**(100) suffers mass spectrum overlap interferences from 168 Er(27.0) and 170 Er(15.0). It can be seen from Table 5, we can know that the interfering appearance concentrations vary from 0.94µgL -1 to 23.29µgL -1. By referring back to Table 4, upon comparison of Table 4 and Table 5, we find that the interfering appearance concentrations arose from matrix mass spectral overlap interferences approach to that of MOH + 2~3 and MO + 2 generated from matrix-induced polyatomic ions. Taking a determination of analytes of interest by selecting other isotopes which are free from matrix mass spectrum overlap interferences is one of the methods which overcome this type of interferences. Separation matrix is the other one of the method of avoiding the interferences described as above. Authorial recently work [21] accomplished successfully with the determination of the 14 REEs as impurities in high purity metal Yb with purity of % by using ICP-MS technique through with making a direct measurement for the analytes as La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er combination with separating Yb matrix by using EHEHP for determination of the analytes as Tm, Lu. In order to resolve this interfering problem, adjusting the instrumental resolution value is the another efficient method. In this work, the variations of intensity of the isotopes of 140 Ce(88.5) in 500µgmL -1 La 2 O 3 solution and that of 168 Er(27.0) and 170 Er(15.0) in 500µgmL -1 Tm 2 O 3 solution are observed under different resolution values. These are listed in Figure 6. Intensity (10 5 cps) Ce in 500 ugml -1 La 2 O Er in 500 ugml -1 Tm 2 O Er in 500 ugml -1 Tm 2 O Resolution (amu) Fig. 6. Intensity vs. resolution for 140 Ce, 168 Er, 170 Er in matrix solutions of 500µgmL -1 of La 2 O 3 and Tm 2 O 3 respectively Fig. 7. Matrix mass spectrum of 500µgmL -1 La 2 O 3 solution with the resolution setting to 0.3amu 8

13 It is evident from Figure 6 that the intensity of 140 Ce(88.5), 168 Er(27.0) and 170 Er(15.0) decreases constantly with the adjustment of the instrumental values varying from 0.7amu to 0.3amu. The matrix mass spectrum were obtained by using a solution of 500µgmL -1 for La 2 O 3 and 500µgmL -1 for Tm 2 O 3 with the resolution values setting to 0.3amu and that are given in Figure 7 and Figure 8. It is apparent that the mass spectrum of the neighbouring isotope of 140 Ce(88.5), 168 Er(27.0) and 170 Er(15.0) at mass of 140,168, 170 are completely separate from that of matrix of 139 La(99.9) and 169 Tm(100) at mass of 139 and 169. Through this experiment described as above, we can get an conclusion that it is possible that we can determinate directly the trace neighbouring analytes with concentrations vary from 0.xµgL -1 to xµgl -1 in some high purity (99.999%) rare earth products with a solution of matrix of 500µgmL -1 without using a complex procedure of separating matrix. For example, in the determination of trace amount of REEs as impurities in high purity Er 2 O 3 (purity was %) by using ICP-MS technique, since the analyte of Ho and Tm both have only one naturally occurring isotope of 165 Ho(100) and 169 Tm(100), that is the measurement of monoisotopes of 165 Ho(100) and 169 Tm(100) suffer the interferences arose from Er matrix mass spectrum overlap interferences, so the determination of high purity Er 2 O 3 (99.999%) was exactly difficult except for using a complex procedure of separating matrix. In this work, we measured directly the trace amount of 12 REEs in high purity Er 2 O 3 (99.999%) by using ELAN 9000 ICP-MS with the instrumental resolution value setting to 0.7amu and obtained that of the monoisotopes of 165 Ho(100) and 169 Tm(100) with the resolution value setting to 0.3amu. We also measured directly the concentrations of isotopes of 165 Ho(100) and 169 Tm(100) with the resolution value setting to 0.7amu, the concentrations of 165 Ho(100) and 169 Tm(100) were 22.7µgL -1 and 3.7µgL -1 in Er matrix solution of 500µgmL -1. Fig. 8. Matrix mass spectrum of 500µgmL -1 Tm 2 O 3 solution with the resolution setting to 0.3amu As is clear from Table 6, the concentrations with the determination the for monoisotopes of 165 Ho(100) and 169 Tm(100) are 1.72µgL -1 and 0.39µgL -1 respectively in a 500µgmL -1 Er 2 O 3 (99.999%) solution with the resolution value setting to 0.3amu and it is much lower than that obtained respectively with the resolution value setting to 0.7amu by using ELAN 9000 ICP-MS. 139 La Table 6 Results for trace of 14 REEs (µg g -1 ) in high purity Er 2 O 3 (99.999%) 140 Ce 141 Pr 143 Nd 147 Sm 151 Eu 155 Gd 159 Tb Dy 165 Ho 169 Tm 172 Yb 175 Lu 89 Y REEs

14 2005 PerkinElmer ICP-OES ICP-MS 3.5 Relationship between the interfering effects and instrumental conditions By referring back to the parts of 3.1 to 3.4, we can find it is the most serious interference of the MO + generated from matrix-induced polyatomic ions with the producing ratio amount to about from 2.0% to 3.0%. Generally speaking, the concentration of a matrix solution is controlled 500µgmL -1 for the determination of trace amount of REEs in high purity rare earth products by using ICP-MS, so the concentrations of interfering MO + vary from 10µgmL -1 to 15µgmL -1. We must take some measures for reducing these interferences that affect the determination with accuracy of REEs of interest. In this work, it was investigated that the relationship between the intensity of matrix-induced polyatomic ions and the instrumental conditions with a 500µgmL -1 La 2 O 3 solution Relationship between matrix-induced polyatomic ions and RF power In the presence of the resolution value setting to 0.7amu and nebulizer gas flow to 0.9 Lmin -1, adjusting RF power to 800, 900, 1000, 1100 and 1200w respectively, the intensity of the polyatomic ions, such as 139 LaO +, 139 LaOH +, 139 LaOH + 2, 139 LaOH + 3 and 139 LaO + 2 changing with the adjustments was observed with a 500µgmL -1 La 2 O 3 solution. These are given in Figure 9. Intensity (cps) RF Power (w) 139 LaO + / LaOH + / LaOH + 2 / LaOH + 3 / LaO + 2 /10 4 Fig.9. Intensity vs. RF power of polyatomic ions in 500µgmL -1 La 2 O 3 solution It can be seen from Figure 9 that the 139 LaO + intensity (up to x 10 8 cps) continuous decreases with RF power constantly increasing. At the end of RF power equals to 1200w, the 139 LaO + intensity arrives at the most lowest value. In opposition to this, the intensity of 139 LaOH + (up to x 10 7 cps) continuous increases with RF power constantly increasing. When the value of RF power equals to 1100w, the intensity of 139 LaOH + remains approximately constant. The phenomenons of the intensity of 139 LaOH + 2 (up to x 10 6 cps) and 139 LaOH + 3 (up to x 10 4 cps) value with adjusting RF power value are very similar to that of 139 LaO + and 139 LaOH + respectively. However, the intensity of 139 LaO + 2 (up to x 10 4 cps) continuous increases with RF power constantly increasing. When the value of RF power equals to 1000w, the intensity of 139 LaO + 2 reaches the most highest value and then arrives at the most lowest value while RF power equals to 1100w, at the end, the intensity of 139 LaO + 2 continuous increases with RF power constantly increasing. As mentioned above, in a practical analysis procedure, it is favour of decreasing the polyatomic ions interferences of MO + and MOH + 2 with increasing RF power and is also favour of decreasing that of MOH +, MOH + 3 and MO + 2 with decreasing RF power Relationship between matrix-induced polyatomic ions and nebulizer gas flow Nebulizer gas flow is another important factor that affects the polyatomic ions interferences which interfere the determination of analytes of interest by using ICP-MS technique. In case of resolution value setting to 0.7amu and RF power to 1000w individually, adjusting nebulizer gas flow to 0.90, 0.91, 0.92, 0.93, 0.94 and 0.95 Lmin -1 respectively, the intensity of polyamotic ions, such as 139 LaO +, 139 LaOH + 1-3, 139 LaO + 2 change with adjustment of nebulizer gas flow was investigated by using a 500µgmL -1 La 2 O 3 solution. These are shown in Figure 10. From Figure 10 it is apparent that the intensity of polyatomic ions of 139 LaO +, 139 LaOH LaO and 2 continuous increases with nebulizer gas flow constantly increasing. Therefore, it is favour of decreasing the polyatomic ions interferences arose from matrix-induced with decreasing nebulizer gas flow. 10

15 2005 PerkinElmer ICP-OES ICP-MS Intensity (cps) Fig. 10. Intensity vs. Nebulizer gas flow of polyatomic ions in 500ugmL -1 La 2 O 3 solution 3.6 Appearance concentration of polyatomic ions arose from matrix-induced In the presence of setting the resolution value to 0.7amu, RF power to 1000w and nebulizer gas flow to 0.9Lmin -1, we took a quantitative determination of appearance concentrations of polyatomic ions generated from matrix-induced in nine high purity rare earth products by using ELAN 9000 ICP-MS. These results were calculated with the same equation as party 3.3 of equation (2), and then the concentrations are given in Table 7. The results of polyatomic ions arose from matrix-induced of high purity of Y, Ho, Er, Tm, Yb and Lu in a 500µgmL -1 solution are not given in Table 7, the reason for this is that the mass range of polyatomic ions generated from the matrix like that does not cover the mass range of trace of amount REEs which will be measured in this samples. It can be seen from Table 7 that the appearance concentrations of polyatomic ions arose from matrix-induced are from to 17.49µgmL -1. Table 7 Appearance concentration (µgml -1 ) of polyatomic ions generated from matrix (n=3) Matrix Polyatomic ion Interfered Mass Appearance concentration La Ce Pr Nd Nebulizer gas flow (Lmin -1 ) 139 LaO + / LaOH + / LaOH + 2 / LaOH + 3 / LaO + 2 / LaO LaOH LaOH LaOH LaO CeO CeOH CeO CeOH CeOH CeOH CeOH CeO CeO CeOH PrO PrOH PrOH PrOH Pr O NdO NdO NdOH NdO NdOH NdOH NdO NdOH NdOH NdO NdOH NdOH NdOH NdOH NdOH NdO NdOH NdOH NdOH NdOH NdO NdOH NdOH NdOH NdOH NdOH

16 2005 PerkinElmer ICP-OES ICP-MS Sm Eu Gd Tb Dy 144 SmO SmOH SmOH SmO SmOH SmO SmOH SmO SmOH SmOH SmO SmOH SmOH SmOH SmOH SmOH SmOH SmO SmOH SmOH SmOH SmOH SmO SmOH SmOH SmOH SmOH SmOH EuO EuOH EuO EuOH EuOH EuOH EuOH EuOH GdO GdO GdOH GdO GdOH GdOH GdO GdOH GdOH GdOH GdO GdOH GDOH GdOH GdOH GdOH TbO DyO DyO DyOH DyOH LOQs and acquiring purity under direct determination of fifteen high purity rare earth products The LOQs and the acquiring purity under direct determination for trace of REEs as impurities in fifteen high purity rare earth products by using ELAN 9000 ICP-MS technique were presented in this part. The LOQs for trace of REEs impurities are defined as the corresponding concentration values of ten times of the stand deviation (10δ) in eleven measurements of 1% HNO 3 blank solution and with consideration of dilution factors of the samples. On the other hand, the LOQs for those trace of REEs impurities that suffer the overlap interferences arose from isobaric, polyatomic ions and mass spectrum overlaps generated from matrix in some high purity rare earth products under direct determination using ICP-MS are defined as the corresponding concentration values of ten times of the stand deviation (10δ) in eleven measurement of 500µgmL -1 matrix solutions. Higher abundant isotopes of REEs of interest in fifteen high purity rare earth products were also selected along with consideration of isotopes free from the overlap interferences arose from that described as above in case of direct determination using ICP-MS without separation procedure of matrix. The LOQs and acquiring purity under direct determination are given in Table 8. The acquiring purity refers to here the capabilities of the method under direct determination of the trace of REEs impurities in high purity rare earth products by using ICP-MS technique with consideration of total LOQs of all of the 12

17 2005 PerkinElmer ICP-OES ICP-MS REEs impurities. The values are calculated as the following equation: 100-(Σ LOQ x 10-6 ) 100% Where : Σ LOQ x refers to total LOQs for the fourteen trace of REEs impurities in a high purity rare earth product 10-6 refers to the coefficient of unit for µg converts as g 4. Conclusions A series of mass spectrum interferences, the appearance concentrations of overlap interferences and polyatomic ions arose from matrix-induced and overcoming these interfering problems et al. in the determination of trace of amount of REEs as impurities in fifteen high purity rare earth products by using ELAN 9000 ICP-MS technique were reported in this paper. No influence of mass spectrum overlap interferences of polyatomic ions arose from lasma- and matrix solvent-induced that can affect the accurate determination of REEs in high purity products because the mass rage of these interfering ions is less than 80 Isobaric overlap interferences between some REEs can be overcame by selecting isotopes that free from overlap interference or establishing correction equations. The interferences caused by matrix-induced polyatomic ions can be partly overcame by using the method of matrix-match, but separation of matrix is the most efficient method to avoid these interferences. The overlap interferences caused by matrix can be resolved by selecting isotopes that free from overlap interference or by separation of matrix, but through adjusting the resolution value is a simple method to avoid these interferences sometimes. Table 8 LOQ (µg g -1 ) and acquiring purity (%) under direct determination of fifteen high purity rare earth products Matrix La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Y Analyte Isotope La --- LOQ Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Isotope LOQ Isotope LOQ Isotope LOQ Isotope LOQ Isotope LOQ Isotope LOQ Isotope LOQ Isotope LOQ Isotope LOQ Isotope LOQ Isotope LOQ

18 2005 PerkinElmer ICP-OES ICP-MS Yb Lu Y Isotope LOQ Isotope LOQ Isotope LOQ ΣLOQ x Acquiring purity 6N 4N 4N 2N 3N 3N 2N 2N 4N 6N 4N 6N 4N 6N 6N Note: 2N refers to the purity for 99% of a high purity rare earth product, 3N for 99.9%, 4N for 99.99% and 6N for %. --- Acknowledgements This work was supported by the important item [No. (2004) 210] of Jiangxi provincial Department of Science and Technology. Reference [1] C. R. Lalonde, J. I. Dalton, Can. J. Spectrosc. 26 (1982) 163. [2] E. S. Gladney, N. W. Bower, Geostand. Newsl. 9 (1985) 261. [3] J. G. Crock, F. E. Lichte, Anal, Chem. 54 (1982) [4] S. S. Biswas, R. Kaimal, A. Sthumadhavan, P. S. Murty, Anal. Lett. 24 (1991) [5] N. Daskalova, S. Velichkov, N. Krasnobaeva, P. Slavova, Spectrochim. Acta 47(1992) E1595. [6] R. S. Houk, V. A. Fassel, G. D. Flesch, H. J. Svec, A. L. Gray, C. E. Taylor, Inductively coupled argon plasma as an ion source for mass spectrometric determination of trace elements, Anal. Chem. 52 (1980) [7] K. E. Jarvis, A. L. Gray, R. S. Houk, Handbook of inductively coupled plasma mass spectrometry, Blackie, Glasgow, [8] C. J. Park, G. E. M. Hall, Analysis of geological matericals by inductively coupled plasma mass spectrometry with sample introduction by electrothermal vaporization, J. Anal. Aton. Spectrom, 3 (1998) [9] K. G. Heumann, Trace determination and isotope analysis of the elements in life sciences by mass spectrometry, Biomed, Mass spectrum, 12 (1985) [10] J. L. Liu, Y. D. Tong, X. Q. Zhang, Determination of trace impurities of rare earth elements in high purity yttrium oxide by ICP-MS, J. Rare Earths. 13 (1995) [11] X. Q. Zhang, Y. D. Tong, J. L. Liu, Determination of trace rare earth elements in high purity cerium oxide by ICP-MS, Fenxi Ceshi Xuebao, 17 (1998) [12] X. Q. Zhang, J. L. Liu, Y. M. Jiang, Y. Yi, T. D. Tong, P. Lin, Determination of impurities in high purity samarium by ICP-MS, Fenxi Ceshi Xuebao, 24 (2005) [13] W. R. Pedreira, J. E. S. Sarkis, C. Rodrigues, I. A. Tomiyeshi, C. A. da siva Queiroz, A. Abrao, Determination of trace amounts of rare earth elements in high pure praseodymium oxide by double focusing inductively coupled plasma mass spectrometry and high-performance liquid chromatography, J. Alloys and compounds, (2001) [14] W. R. Pedreira, J. E. S. Sarkis, C. A. da siva Queiroz, C. Rodrigues, I. A. Tomiyeshi, A. Abrao, Determination of trace amounts of rare-earth elements in high pure neodymium oxide by ICP-SFMS and HPLC techniques. J. Solid sate Chemistry, 171 (2003) 3-6. [15] M. A. Vaughn, G. Horlick, Oxide, hydroxide and doubly charged species in inductively coupled plasma mass spectrometry. Appl. Spectrosc, 40 (1986) [16] A. L. Gray, Mass spectrometry with an inductively coupled plasma as an ion source: the influence on ultra trace analysis of background and matrix response. Spectrochim, Acta. 41B (1986) [17] S. H. Ta, G. Horlick, Background spectral features in inductively coupled plasma mass spectrometry. Appl. Spectrosc. 40 (1986) [18] X. Q. Zhang, J. L. Liu, Y. M. Jiang, Y. Q. Suo, Y. L. Liu, X. Li, Determination of trace REEs and Non-REEs impurities in high purity lanthanum oxide by ICP-MS, J. Chinese mass spectrometry society.25 (2004) [19] M. Yin, B. Li, T. F. Fu, Determination of rare earth impurities in high purity Sc 2 O 3, Y 2 O 3 Ho 2 O 3, Tm 2 O 3 and Lu 2 O 3 by ICP-MS, J. Analytical science. 11(1995) [20] B. Li, Y. Zhang, M. Yin. Determination of trace amount of rare earth elements in high-purity cerium oxide by ICP-MS after separation by solvent extration, Analyst. 122 (1997) 543~547. [21] X. Q. Zhang, J. L. Liu, Y. Yi, Y. M. Jiang, P. Lin, Y. D. Tong, Determination of trace impurities of trace impurities in high purity ytterbium by ICP-MS, Fenxi Ceshi Xuebao, 23 (2004)

19 2005 PerkinElmer ICP-OES ICP-MS Direct Determination of Rare Earth Impurities in High Purity Ytterbium Oxide by Inductively Coupled Plasma Mass Spectrometry Xinquan Zhang*, Jinglei Liu, Xiang Li, Yonglin Liu, Yong Yi, Yumei Jiang, Yaqin Su Jiangxi Institute of Analyzing and Testing, Beijing East Road 171, Nanchang , Jiangxi Province, China Abstract A novel methodology was developed for the direct determination of trace quantities of rare earth elements (REEs) in high purity ytterbium oxide by inductively coupled plasma mass spectrometry (ICP-MS) in this work. The mass spectra overlap interferences arose from Yb matrix on the neighbouring analytes of 169 Tm(100) and 175 Lu(97.4) were eliminated by adjusting instrumental peak resolution value from 0.7amu to 0.3amu. The matrix suppression effect of Yb on the ion peak signals of REEs impurities was compensated effectively for the addition with internal standard as In. The limit of quantitation (LOQ) of REEs impurities was from µgg -1 to 0.022µgg -1, the recoveries of spiked sample for REEs were found to be in the rage of 91.2%~105% through the use of proposed method and relative standard deviation (RSD) varied between 3.1% and 7.2%. The novel methodology had been found to be suitable for the direct determination of trace REEs impurities in %~ % high purity Yb 2 O 3. Keywords: Direct determination; Rare earth impurity; High purity ytterbium oxide; Inductively coupled plasma mass spectrometry 1. Introduction With the development of widely applications of high purity rare earth products in many material fields, such as phosphor materials in a display, gain media in a solid state laser, optomagnetic materials in an optical isolator and high temperature superconductor, etc., the REEs are increasing their importance in many industrial fields. Therefore, a sensitive, rapid and reliable analytical method for trace analysis of REEs impurities in high purity rare earth products is strongly required for quality control, product certification and evaluation of material performance. After Houk et al. [1] first published their methodology by using inductively coupled plasma (ICP) as an ion source combination with mass spectrometer (MS), twenty five years have passed. Today, this analytical technique regarded as a principal measure is widely applied in the analytical fields such as high purity materials, environment, metallurgy, biochemistry et al. due to its attractive and excellent performance in terms of high sensitivity, low determination 15

20 2005 PerkinElmer ICP-OES ICP-MS limits, determination capability of multielements at trace or ultra-trace at the same time and wide dynamic rage compared with other analytical techniques such as inductively coupled plasma atomic emission spectrometry (ICP-AES), so, it becomes the major analytical method used for the determination of trace of REEs impurities in high purity rare earth products day by day [2-9]. Although ICP-MS technique possesses protrusive advantages described as above, some major problems encountered in the application of this measure to the determination of trace REEs in high purity rare earth products are the matrix suppression effect and the mass spectra interferences arose from isobaric overlap, polyatomic ions and overlap interferences generated from parent matrix except for the measurement of trace of REEs impurities in high purity Y, Ho, Tm, Lu products employed with ICP-MS technique [5, 7]. The matrix suppression effect could be compensated for adding internal standard [2, 5, 6], but these overlap interferences may restrict its direct applicability for the determination of trace of REEs impurities in high purity rare earth products. From the literature reports, many attempts had been made to solve these interferences with the procedure of separation of trace quantities of REEs impurities from the sample matrix. Pedreira et al [10,11] investigated the determination of rare earth analytes as impurities in high purity La 2 O 3 and Pr 6 O 11 with ICP-MS combined with high-performance liquid chromatography(hplc) technique after parent matrix as La and Pr had been separated respectively by HPLC. Otherwise, the techniques of ion chromatography (IC) and eletrothermal vaporation(etv) combined with ICP-MS were employed for separation of the trace of REEs impurities from parent matrix to overcome these overlap interferences[12,13]. In case of %~ % high purity Yb 2 O 3 analytical procedure employed with ICP-MS, overlap interferences generated from Yb matrix lead to the failure in direct measurement of Tm, Lu. Several papers evaluated for the determination of trace of REEs in high purity Yb 2 O 3 using ICP-MS technique. Cai et al. [14] determined thirteen trace quantities of REEs in high purity Yb 2 O 3 using ICP-MS based on Ga internal standard, but the important analyte value of Lu was not reported because of the mass spectra overlap interferences arose from parent matrix of Yb. Zhang et al. [15] accomplished recently with the determination of 14 REEs as impurities in % high purity metal Yb using ICP-MS technique through with making a direct measurement for the analytes as La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er combination with separating Yb matrix by using 2-ethlhexyl hydrogen-2-ethylhexylphosphonate (EHEHP) as solvent extraction for the determination of analytes of Tm and Lu. However, in these multi-stage combined procedures, a risk of increasing contamination and worsening LOQs may be encountered. It can also spend a long time and is difficult to grasp sometimes, because the concentration large difference between matrix (1000µgmL -1 ) and trace quantities of REEs impurities (0.00xµgmL -1 ) can amount to about or more. Direct determination of trace quantities of REEs impurities in high purity rare earth products has the advantages of minimizing sample preparation, reducing the potential for sample contamination and simplest manipulation comparing with those procedures described as above of separation parent matrix. In this work, with the aid of adjusting the instrumental peak resolution, the overlap interferences arose from Yb matrix on the neighbouring analytes of Tm and Lu were overcame, it was realized that the direct determination of trace quantities of 14 REEs in %~ % high purity Yb 2 O 3 employed with ICP-MS technique, to our best knowledge, this was not reported. 2. Experimental 2.1 Instrument A Perkin-Elmer Sciex ELAN 9000 ICP-MS equipped with a integrated peristaltic pump and a cross flow nebulizer combined with a scott spray chamber which was made from Ryton material was used. The instrument conditions are summarized in Table 1. 16