An Overview of Magnetic Sector Inductively Coupled ICP and GD-MS. Isaac (Joe) Brenner

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1 An Overview of Magnetic ctor Inductively Coupled ICP and GD-MS Isaac (Joe) Brenner Environmental rvices, 9 Dishon Street, Malkha, Jerusalem, Israel, brenner@cc.huji.ac.il Abstract Although Inductively Coupled Plasma Quadrupole-based Mass Spectrometry (ICP- QMS) is a well established technique for multitrace element determinations, it has limitations due to plasma and matrix derived spectroscopic interferences that result in degeneration of detection limits and biased analytical results. Therefore, unambiguous separation of analyte ions from spectroscopic interferences is a prerequisite of accurate and precise elemental analysis. veral strategies have been employed to reduce these interference effects: tedious and contamination prone preconcentration and matrix separation procedures, correction equations, front-end sample introduction, plasma optimization, collision and reaction cells and high resolution magnetic sector ICP-MS (HR-MS-ICP-MS). In this overview we will focus on instrumentation and application of HR-MS-ICP-MS) and glow discharge (GD) MS for determination of low analyte concentrations in solutions and in solid samples. Introduction Quadrupole-based inductively coupled plasma mass spectrometry (ICPQMS) with and without collision-reaction cells is now accepted as an efficient tool for ultra trace element determinations. However there are significant analytical limitations in their application owing to insufficient resolving power. Quadrupole-based systems, characterized by a resolution of amu are inadequate for resolving numerous matrix-induced polyatomic interferences. In these cases collision-reaction cells have been used with a myriad of different gases and flow rates and RPq cutoff values to compensate for these interferences. High resolution double-focusing magnetic-sector spectrometers, coupled to inductively coupled plasma (HR-MS-ICP-MS) and a glow discharge (GD) source have been widely employed for the analysis of complex liquid and solid samples. These instruments are characterized by enhanced limits of detection in the ppq-sub ppq range and outstanding resolving power amounting to 10,000. This resolving power allows many interfered analytes such as the REEs, Fe, As, V, Cr to be determined quantitatively in complex and unknown samples In this presentation, the current instrument configurations and applications will be reviewed. Instrumentation In the Nier-Johnson HR-MS-ICP-MS, there is an electromagnet and an electrostatic analyzer (ESA); in the "forward" configuration, the ESA is located before the magnet, and in the reverse design it is positioned after. A schematic of the Thermo Fisher reverse Nier- Johnson Element 2 spectrometer is illustrated in Figure 1. Ions derived from samples and plasma enter the electromagnet (which is dispersive with respect to ion energy and mass),

2 and are focused with diverging angles of motion. In the ESA ions are dispersed according to ion energy and focused onto variable exit slits. In double focusing instruments, ion angles and ion energies focus ions of a particular mass-to-charge into the detector. Data acquisition When the magnet is scanned to a defined mass, an electric scan is then employed to cover a mass window of %. Multiple points are then used to measure analyte peaks and other masses of interest. With state of art instruments, a full mass scan (0 250 amu) can be made in the order of 200 ms. This rate is somewhat slower than ICP-QMS. Nevertheless, routine applications with laser ablation and other transient signal applications can be made. Resolving power and overcoming spectroscopic interferences In addition to enhanced subppq LODs, the excellent and variable resolving power of magnetic-sector ICP-MS instruments amounting to 10,000 (5 % peak height/10 % valley definition), can differentiate the majority of plasma and sample induced spectroscopic interferences (Table 1). In the Thermo Fisher Element 2 HR-MS-ICP-MS, mass resolution is achieved by using slits one at the entrance to the spectrometer, another at the exit, before the detector. Low resolution is obtained using wide slits, whereas high resolution is achieved with narrow slits (Figure 2). This figure shows that flat top peaks are obtained at low resolution (300), whereas triangular peaks are obtained at high resolution (8000). However, with decreasing resolution, ion signals decrease substantially (Figure 3). Nevertheless, it should be emphasized that detection limits even at low resolution exceed those obtained in quadrupolebased systems. Moreover what is more important than instrument LODs are so-called TRUE LODs LODS that can be realistically and routinely obtained when analyzing real samples in the presence of interferences! The advantage of variable and high resolution is that plasma and sample derived polyatomic interferences can be separated as needed. Figure 4 compares the mass spectrum of 56 Fe and Ar 16 O using a quadrupole instrument and a magnetic sector instrument. In the latter case these masses were separated at a resolution of about 2500 and in the former, these peaks cannot be resolved. Limits of Detection In addition to high resolving power of magnetic-sector instruments is the outstanding typical very high sensitivity of 1G and extremely low background levels of < 0.1 cps as a result the LODs even at low resolution exceed those obtainable using a quadrupole instrument. Figure 5 shows as mass scan of Ra indicating an LOD in the Range of femtograms. Precision At low resolution using flat top peaks, % relative standard deviations (% RSD) of 0.01 can be obtained routinely for the determination of isotope ratios (Table 2). At high resolution, precisions of 0.1% RSD are attained.

3 Applications A wide range of applications in geosciences, nuclear and advanced material technologies, biology and speciation will be described. Multicollectors In multicollector ICP-MS (MC-ICP-MS), simultaneous detection of ions produces isotope ratio RSDs comparable to those obtained by TIMS. The former instruments are used widely for isotope ratio determinations in geo and environmental investigations using conventional sample introduction, laser ablation and transient GC coupling for speciation. Conclusions HR-MS-ICP-MS and glow discharge are characterized by very high sensitivity, high and variable resolution and ultrahigh-precision. These favorable instrument characteristics and performance are particularly important in geochemistry and isotope environmental science and nuclear technologies. Multicollector coupled ICP MS systems extend the scope of reconstructing the paleo-environment and geochronology. Glow discharge direct solids analysis is an important tool for surface analysis, metallurgy, nuclear and advanced materials technologies. Dr. Isaac (Joe) Brenner currently serves as a senior scientist and research director at the Environmental Analytical Laboratory (EAL), as a senior consultant for QA/QC, iso accreditation and method validation at the Dan Region of Cities Authority for Effluents and the Environment in Israel. He is a certified auditor for ISO for analysis and waters and wastes using compliant plasma-based procedures. He obtained his Ph.D. in Geochemistry from the Hebrew University, Jerusalem, Israel in Dr. Brenner is a visiting professor in the Department of Earth Sciences, National Cheng Kung University, Tainan, Taiwan, a guest scientist with the Institute of Chemistry and Radiochemistry, Technical University, Graz, Austria, the Institute of Analytical Chemistry, Autonoma University, Barcelona, Spain, and the Faculty of Sciences and Environmental Studies, University de Castilla-La Mancha, Antigua Fabrica de Armas, Toledo Spain, previously at the Department of Environmental Analytical Chemistry, Chuo University, Tokyo, Japan, and Laboratoire de Chimie Analytique Bio Inorganique et Environnement, (LCABIE) CNRS, Pau, France. In all these appointments he is involved in development of methods for analysis of environmental, geo-environmental and refractory materials using ICP-AES and MS, environmental studies using trace elements and isotope ratios.. Dr Brenner has extensive experience in the development and implementation of plasma-based analytical methodologies using ICP-AES and ICP-MS for environmental samples. He was the application laboratory manager in Jobin Yvon, Longjumeau, France, a

4 senior analytical adviser at the Varian Research Center, Palo Alto, California, USA, and for ICP-MS using collision cells, high ion transmission and robust interfaces at Thermo Elemental, Winsford, UK and with Thermo Fisher Scientific in Madrid, Spain. In Spain Brenner is a senior application and special project adviser for compliant methods of analysis of waters and wastes. Dr Joe Brenner has delivered more than 0 presentations, short courses, round table discussions at universities, international symposiums, research institutes, and instrument manufacturer forums; he has 100 peer-reviewed scientific publications. He has delivered numerous short courses on compliant methods of analysis of water and wastes, geoanalysis, sample preparation, direct solids analysis, and magnetic sector ICP-AES and MS worldwide. M/Z 51 V 52 Cr 53 Cr 54 Cr 54 Fe 55 Mn 56 Fe 57 Fe 58 Ni 59 Co 65 Cu Table 1. Problems of analysis of Ca-Na-Ca- Cl waters- Polyatomic ion interferences Polyatomic ions 35 Cl 16 O Ar 12 C, 36 Ar 16 O, 35 Cl 16 O 37 Cl 16 O, 35 Cl 18 O 37 Cl 16 OH 38 Ar 16 O, 37 Cl 16 OH 37 Cl 18 O Ar 16 O, Ca 16 O Ca 16 OH 42 Ca 16 O 43 Ca 16 O 25 Mg Ar M/Z 60 Ni 63Cu 64 Zn 66 Zn 75 As Sr Polyatomic ions 44 Ca 16 O, 23 Na 37 Cl, 24 Mg 36 Ar Na 23 Ar 48 Ca 16 O, 26 Mg 38 Ar, 35 Cl 28 NH 26 Mg Ar Ar 35 Cl Ar 36 Ar Ar 37 Cl 38 Ar Ar Ar 2, 79 BrH 81 BrH 48 Ca Ar 1

5 Table 2 High precision for isotope ratios Heumann et al., JAAS, 13 (1998) Type of instrument RSD% ICP-QMS ICP-SFMS (single) ICP-TOFMS ICP-MCMS TIMS GDMS GIRMS < factor 10 better comparable GIRMS superior 2 Figure 1 Principle components of SF ICP-MS Electro Static Analyzer Dual mode ion detector Slit Electro Magnet Mass paration Sample Introduction Transfer and focusing ion optics Plasma interface Ion generation Laser HPLC GC FFF CE. 3

6 Figure 2 1 Figure 3. Transmission vs. resolution (Axiom) 100 % Transmission RP - 100% 3,000RP - 20% 6,000RP - 8% 10,000RP - 4% Resolution (Resolving Power, RP) 5

7 Figure 4 Resolution of ArO + from 10 ng/l 56 Fe + 10 ppt Fe Ar 16 O + 56 Fe + 6 Figure 5 Background mineral water 5% HNO 3 ~200 fg/l 226 Ra Low Resolution bkg <0.2 cps bkg <0.2 cps 7