Advanced Analytical Chemistry – CHM 6157® Y. CAIFlorida International University Updated on 9/13/2006Chapter 3ICPMS 1. References: John R. Dean, Atomic Absorption and Plasma Spectroscopy, Wiley. Steve J. Hill, Inductively Coupled Plasma Spectrometry and Its Applications, CRC Press. K.E. Jarves, A.L. Gray, and R.S. Houk, Handbook of Inductively coupled Plasma Mass Spectrometry, 1997, Blackie Academic & Professional. A. Montaser and D.W. Golightly, Inductively Coupled Plasma in Analytical Atomic Spetcrometry, 1987, VCH. J.W. Robinson: Atomic Spectroscopy, Second Edition, Revised and Expended, C. Vandecasteele, and C.B. Block: Modern methods for Trace Element Determination, 1997.

Advanced Analytical Chemistry – CHM 6157® Y. CAIFlorida International University Updated on 9/13/2006Chapter 3ICPMS-1 1. AGILENT 7500

Advanced Analytical Chemistry – CHM 6157® Y. CAIFlorida International University Updated on 9/13/2006Chapter 3ICPMS 1. Inductively Coupled Plasma Mass Spectrometry (ICPMS) 1.Fundamental aspects of ICPMS Briefly, in this technique, singly charged analyte ions generated in an ICP are extracted into and measured with a mass analyzer. The rapid development of ICPMS has been fueled by its unique measurement capabilities Detection Limit: 1 to 100 ng/L In many cases, these limits are 100 to 1000 times superior to those that can be routinely achieved by ICP-AES. Spectral interferences Isotopic ratio measurement capability

Advanced Analytical Chemistry – CHM 6157® Y. CAIFlorida International University Updated on 9/13/2006Chapter 3ICPMS 1.1ICP as an ion source When a system is in thermal equilibrium, the degree of ionization of an atom is given by the Saha equation (Note that the degree of excitation of an atom is described by Boltzmann equation: n i n e /n a = 2Z i /Z a (2πmkT/h 2 ) 3/2 exp(-E i /kT) where n i, n e and n a are the number densities of the ions, free electrons and atoms in the plasma, respectively. Z i and Z a are the ionic and atomic partition functions, respectively. m is the electron mass. k is the Boltzmann constant. T is the temperature. h is the Planck’s constant. E i is the first ionization energy.

Advanced Analytical Chemistry – CHM 6157® Y. CAIFlorida International University Updated on 9/13/2006Chapter 3ICPMS Degree of ionization is dependent on: electron number density temperature ionization energy Assume: electron number density for an argon ICP: 4 x cm -3 ionization temperature: 8730 K Then the degree of ionization as a function of first ionization energy, predicted by the Saha equation.

Advanced Analytical Chemistry – CHM 6157® Y. CAIFlorida International University Updated on 9/13/2006Chapter 3ICPMS Over 80% ionized for elements having 1st ionization energies of less than 9 eV. The most poorly ionized elements: He, Ne, F, O, and N (<1%); Kr and Cl (1 – 10%) C, Br, Xe and S (10 –30%),P, I, Hg, As, Au and Pt (30 –80 %). Note that this calculation is carried out based on assumption of a local thermodynamic equilibrium (LTE) be reached. From Jarvis et al., 1997

Advanced Analytical Chemistry – CHM 6157® Y. CAIFlorida International University Updated on 9/13/2006Chapter 3ICPMS 1. Jarvis et al., 1997

Advanced Analytical Chemistry – CHM 6157® Y. CAIFlorida International University Updated on 9/13/2006Chapter 3ICPMS 1. Jarvis et al., 1997

Advanced Analytical Chemistry – CHM 6157® Y. CAIFlorida International University Updated on 9/13/2006Chapter 3ICPMS 1.

From Houk ICP Course Advanced Analytical Chemistry – CHM 6157® Y. CAIFlorida International University Updated on 9/11/2004Chapter 2Plasma Atomic Emission Spectrometry YO, Y(I), Y(II) EMISSION ZONES COURTESY VARIAN 1.2Distribution of ions in the plasma

Advanced Analytical Chemistry – CHM 6157® Y. CAIFlorida International University Updated on 9/13/2006Chapter 3ICPMS 1. Jarvis et al., 1997 Cooler central Hotter area

Advanced Analytical Chemistry – CHM 6157® Y. CAIFlorida International University Updated on 9/13/2006Chapter 3ICPMS 1. Jarvis et al., 1997 The optimized location of the orifice is determined by the elements of interest and other plasma conditions. Ionization needs time!

Advanced Analytical Chemistry – CHM 6157® Y. CAIFlorida International University Updated on 9/13/2006Chapter 3ICPMS 1. Jarvis et al., 1997 The optimized location of the orifice is determined by the elements of interest and other plasma conditions. Ionization needs time!

Advanced Analytical Chemistry – CHM 6157® Y. CAIFlorida International University Updated on 9/13/2006Chapter 3ICPMS 1.3Ion sampling ICP/AES vis ICP/MS Ion sampling interface

Advanced Analytical Chemistry – CHM 6157® Y. CAIFlorida International University Updated on 9/13/2006Chapter 3ICPMS 1.3.2Boundary layer and sheath Interaction between plasma and sampling cone:  Intermediate temperature zone between plasma and cone (oxide formation) in this boundary layer (red color).  Plasma potential (sheath electrical by the interaction between the plasma and the conducting sampler) Boundary vs. Sheath region

Advanced Analytical Chemistry – CHM 6157® Y. CAIFlorida International University Updated on 9/13/2006Chapter 3ICPMS 1.3.3Supersonic jet Barrel shock Mach disk

Advanced Analytical Chemistry – CHM 6157® Y. CAIFlorida International University Updated on 9/13/2006Chapter 3ICPMS 1.3.3Supersonic jet From Houk ICP Course The barrel shock and Mach are caused by collisions between fast atoms/ions from jet and the back ground gas, which reheat the atoms/ions and induce emission. To avoid losses of ions due to collisions and scattering, position the skimmer with its open tip inside the Mach disc.

Advanced Analytical Chemistry – CHM 6157® Y. CAIFlorida International University Updated on 9/13/2006Chapter 3ICPMS Mach diskSamplerSkimmer

Advanced Analytical Chemistry – CHM 6157® Y. CAIFlorida International University Updated on 9/13/2006Chapter 3ICPMS 1.3.4Ion focusing Serves to focus ions from the skimmer into the mass filter (analyzer) Rejects neutral atoms Minimize the passage of any photons from ICP (Electron Multiplier is photo/neutral sensitive) Extraction (Extract ions from Plasma) Einzel (Focus ion beam) Omega ( eliminate photons &neutrals) Torr Torr

Advanced Analytical Chemistry – CHM 6157® Y. CAIFlorida International University Updated on 9/13/2006Chapter 3ICPMS 1.3.5Space charge effects  Space charge effects are a consequence of the mutual repulsion between particles of like charge.  It is a consequence of Coulomb’s law, which quantifies the force (F) between two point charges (q and q’) separated by a distance r as F = k(qq’/r 2 ) where k is a proportionality constant that depends upon the unit chosen for the other variables in the equation.

Advanced Analytical Chemistry – CHM 6157® Y. CAIFlorida International University Updated on 9/13/2006Chapter 3ICPMS Adapted from Ken Busch, June 2004, 19(6)Spectroscopy.

Advanced Analytical Chemistry – CHM 6157® Y. CAIFlorida International University Updated on 9/13/2006Chapter 3ICPMS Adapted from Jarvis et al. 1997

Advanced Analytical Chemistry – CHM 6157® Y. CAIFlorida International University Updated on 9/13/2006Chapter 3ICPMS 1.4Mass Analyzer (Quadrupole) Skoog et al., 1999, Instrumental Analysis  Two pairs of rods: Attach + and - sides of a variable dc source Apply variable radio-frequency ac potentials to each pair of rods.  Ions are accelerated into the space between the rods by a small potential (5-10V)  Ions having a limited range of m/z value reach the transducer.

Advanced Analytical Chemistry – CHM 6157® Y. CAIFlorida International University Updated on 9/13/2006Chapter 3ICPMS 1.4.1Ion trajectories in a Quadrupole  A pair of positive rods (as lying in the xz plane). In the absence of a dc potential: Positive half of the ac cycle: Converge (ion in the channel will tend to converge in the center of the channel during the positive half of the ac cycle). Negative half of the ac cycle: Diverge (ions will tend to diverge during the negative half). Skoog et al., 1999, Instrumental Analysis Whether or not a positive ion strikes the rod will depend upon the rate of movement of ion along the z axis, its m/z, and the frequency and magnitude of the ac signal.

Advanced Analytical Chemistry – CHM 6157® Y. CAIFlorida International University Updated on 9/13/2006Chapter 3ICPMS  A pair of positive rods (Cont’d) With dc potential: Heavier ions: less affected by ac (largely by dc). Lighter ions: deflected during negative cycle of ac. The pair of positive rods: a high-pass mass filter for positive ions traveling in the xz plane.

Advanced Analytical Chemistry – CHM 6157® Y. CAIFlorida International University Updated on 9/13/2006Chapter 3ICPMS  The pair of negative rods In the absence of the ac potential: All positive ions will tend to strike the rods. With ac potential: For the lighter ions, however, this movement may be offset by the positive half cycle of ac potential. Thus, the pair of negative rods operates as a low-pass mass filter. The mass that can be analyzed can be varied by adjusting the ac and dc potential.

Advanced Analytical Chemistry – CHM 6157® Y. CAIFlorida International University Updated on 9/13/2006Chapter 3ICPMS Skoog et al., 1999, Instrumental Analysis

Advanced Analytical Chemistry – CHM 6157® Y. CAIFlorida International University Updated on 9/13/2006Chapter 3ICPMS 1.4.2Stability diagram a = 4U/(m/z)r 2 ω 2 q = 2V/(m/z)r 2 ω 2 U is the applied DC voltage V is the applied AC voltage m/z is mass charge ratio r is radius between rods ω is frequency The stability diagram is essentially a plot of the parameter a as a function of q.

Advanced Analytical Chemistry – CHM 6157® Y. CAIFlorida International University Updated on 9/13/2006Chapter 3ICPMS a/q = 2U/V consistent M 3 >M 2 >M 1

Advanced Analytical Chemistry – CHM 6157® Y. CAIFlorida International University Updated on 9/13/2006Chapter 3ICPMS R = m/Δm Vandecasteele and Block, “Modern Methods for trace element determination” 1997, p188