Atomic mass spectrometry instrumentation

Figure 1.2 shows the basic instrumentation for atomic mass spectrometry. The component where the ions are produced and sampled from is the ion source. Unlike optical spectroscopy, the ion sampling interface is in intimate contact with the ion source because the ions must be extracted into the vacuum conditions of the mass spectrometer. The ions are separated with respect to mass by the mass analyser, usually a quadrupole, and literally counted by means of an electron multiplier detector. The ion signal for each... 

Gray, A.R., and Williams, J.G. (1987) Oxide and doubly charged ion response of a commercial inductively coupled plasma mass spectrometry instrument. J. Anal. Atomic Spectrom. 2, 81-82. 

Atomic mass spectrometry has been around for many years, but the introduction of the inductively coupled plasma in the 1970s and its subsequent development for mass spectrometry led to its successful commercialization by several instrument companies. Today inductively coupled plasma mass spectrometry (ICP-MS) is a widely used technique for the simultaneous determination of more than 70 elements in a few minutes. Some other sources, such as the glow discharge, are also used for atomic mass spectrometry. Because the ICP predominates, however, the discussion here focuses on ICP-MS. 

Part V covers spectroscopic methods of analysis. Basic material on the nature of light and its interaction with matter is presented in Chapter 24. Spectroscopic instruments and their components are described in Chapter 25. The various applications of molecular absorption spectrometric methods are covered in some detail in Chapter 26, while Chapter 27 is concerned with molecular fluorescence spectroscopy. Chapter 28 discusses various atomic spectrometric methods, including atomic mass spectrometry, plasma emission spectrometry, and atomic absorption spectroscopy. 

A mass spectrometer is an instrument that produces ions and separates them according to their mass-lo-charge ratios, m/z. Most of the ions we will discuss are singly charged so that the ratio is simply equal to the mass pumber of the ion. Several types of mass spectrometers are currently available from instrument manufacturers. In this chapter, we describe the three types that are used in atomic mass spectrometry the quadra-pole mass spearomeier. the lime-of-ftighl mass spectrometer. and the doubk-foctising mass spectrometer. Other types of mass spectrometers are considered in Chapter 20. which is devoted to molecular mass spectrometry. I he first column in Table I l-l indicates the types of atomic mass spectrometry in which each of the three types of mass spectrometer is usually applied. 

Isobaric Interferences. Isobaric species are two elements that have isotopes of csscnually the same mass. For atomic mass spectrometry with a quadrupole mass spectrometer, isobaric species arc isotopes that differ in mass by less than one unit. With higher-resolution instruments, smaller differences can be tolerated. 

There are three primary instrumental approaches to eliminating or reducing interferences in atomic mass spectrometry (1) use of high mass resolution ICP-MS (HR-ICP-MS) (2) use of a collision cell to break apart polyatomic interferences (3) use of gas phase chemical reactions in a reaction cell to eliminate polyatomic interferences. The approach of changing the instrument operating conditions to form a cool or cold plasma has been discussed. 

See also Atomic Absorption Spectrometry Principles and Instrumentation Interferences and Background Correction. Atomic Mass Spectrometry Inductively Coupled Plasma Laser Microprobe. Liquid Chromatography Column Technology. 

See also Activation Anaiysis Neutron Activation. Atomic Absorption Spectrometry Principies and Instrumentation. Atomic Mass Spectrometry Inductiveiy Coupied Piasma. Carbon. Geochemistry Soii, Organic Components. Humic and Fuivic Compounds. Microscopy ... 

Inductively Coupled Plasma. Atomic Fluorescence Spectrometry. Atomic Mass Spectrometry Inductively Coupled Plasma. Chemiluminescence Liquid-Phase. Enzymes Enzyme-Based Electrodes. Fluorescence Instrumentation. Ion-Selective Electrodes Overview. Optical Spectroscopy Detection Devices. Sensors Overview. Voltammetry Overview. 

See alsa Air Analysis Outdoor Air. Atomic Emission Spectrometry Microwave-Induced Plasma. Atomic Mass Spectrometry Inductively Coupled Plasma. Elemental Speciation Overview Practicalities and Instrumentation. Gas Chromatography Environmental Applications. Isotope Dilution Analysis. Isotope Ratio Measurements. 

See also Atomic Mass Spectrometry Laser Microprobe. Bioluminescence. Capillary Electrophoresis Overview. Chemometrics and Statistics Multivariate Calibration Techniques. Extraction Solvent Extraction Principles. Liquid Chromatography Overview Reversed Phase. Mass Spectrometry Principles. Phosphorescence Principles and Instrumentation Room-Temperature. 

See also Atomic Absorption Spectrometry Interferences and Background Correction. Atomic Emission Spectrometry Principles and Instrumentation Interferences and Background Correction Flame Photometry Inductively Coupled Plasma Microwave-Induced Plasma. Atomic Mass Spectrometry Inductively Coupled Plasma Laser Microprobe. Countercurrent Chromatography Solvent Extraction with a Helical Column. Derivatization of Analytes. Elemental Speciation Overview Practicalities and Instrumentation. Extraction Solvent Extraction Principles Solvent Extraction Multistage Countercurrent Distribution Microwave-Assisted Solvent Extraction Pressurized Fluid Extraction Solid-Phase Extraction Solid-Phase Microextraction. Gas Chromatography Ovenriew. Isotope Dilution Analysis. Liquid Chromatography Ovenriew. 

McDaniel, E, Malteson, S., Weathers, D., Marble, D., Duggan, I, Elliott, R, Wilson, D., Anthony, J. (1990) The University of North Texas atomic mass spectrometry facility for detection of impurities in electronic materials and metals. Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms, 52, 310-314. 

Other Mass Spectrometers. Spectrometers such as ion traps and ion cyclotron resonance have also been used in atomic mass spectrometry, but have not yet been incorporated into a commercial instrument. The former instrument has the advantage of ion storage and ion-molecule reaction capability, while the latter instrument is capable of extremely high resolution. 

Section 2 comprises seven chapters devoted to various atomic spectromctric methods, including an introduction to spectroscopy and spectroscopic instrumentation, atomic absorption, atomic emission, atomic mass spectrometry, and X-ray spectrometry. 

A common mistake for beginners in mass spectrometry is to confuse average atomic mass and isotopic mass. For example, the average atomic mass for chlorine is close to 35.45, but this average is of the numbers and masses of Cl and Cl isotopes. This average must be used for instruments that cannot differentiate isotopes (for example, gravimetric balances). Mass spectrometers do differentiate isotopes by mass, so it is important in mass spectrometry that isotopic masses be used... 

In Laser Ionization Mass Spectrometry (LIMS, also LAMMA, LAMMS, and LIMA), a vacuum-compatible solid sample is irradiated with short pulses ("10 ns) of ultraviolet laser light. The laser pulse vaporizes a microvolume of material, and a fraction of the vaporized species are ionized and accelerated into a time-of-flight mass spectrometer which measures the signal intensity of the mass-separated ions. The instrument acquires a complete mass spectrum, typically covering the range 0— 250 atomic mass units (amu), with each laser pulse. A survey analysis of the material is performed in this way. The relative intensities of the signals can be converted to concentrations with the use of appropriate standards, and quantitative or semi-quantitative analyses are possible with the use of such standards. 

In addition to the wet and optical spectrometric methods, which are often used to analyse elements present in very small proportions, there are also other techniques which can only be mentioned here. One is the method of mass spectrometry, in which the proportions of separate isotopes can be measured this can be linked to an instrument called a field-ion microscope, in which as we have seen individual atoms can be observed on a very sharp hemispherical needle tip through the mechanical action of a very intense electric field. Atoms which have been ionised and detached can then be analysed for isotopic mass. This has become a powerful device for both curiosity-driven and applied research. 

In modern times, most analyses are performed on an analytical instrument for, e.g., gas chromatography (GC), high-performance liquid chromatography (HPLC), ultra-violet/visible (UV) or infrared (IR) spectrophotometry, atomic absorption spectrometry, inductively coupled plasma mass spectrometry (ICP-MS), mass spectrometry. Each of these instruments has a limitation on the amount of an analyte that they can detect. This limitation can be expressed as the IDL, which may be defined as the smallest amount of an analyte that can be reliably detected or differentiated from the background on an instrument. 

The most widely regarded approach to accomplish the determination of as many pesticides as possible in as few steps as possible is to use MS detection. MS is considered a universally selective detection method because MS detects all compounds independently of elemental composition and further separates the signal into mass spectral scans to provide a high degree of selectivity. Unlike GC with selective detectors, or even atomic emission detection (AED), GC/MS may provide acceptable confirmation of the identity of analytes without the need for further information. This reduces the need to re-inject a sample into a separate GC system (usually GC/MS) for pesticide confirmation. Through the use of selected ion monitoring (SIM), efficient ion-trap or quadrupole devices, and/or tandem mass spectrometry (MS/MS), modern GC/MS instruments provide LODs similar to or lower than those of selective detectors, depending on the analytes, methods, and detectors. 

Mass spectrometry is the only universal multielement method which allows the determination of all elements and their isotopes in both solids and liquids. Detection limits for virtually all elements are low. Mass spectrometry can be more easily applied than other spectroscopic techniques as an absolute method, because the analyte atoms produce the analytical signal themselves, and their amount is not deduced from emitted or absorbed radiation the spectra are simple compared to the line-rich spectra often found in optical emission spectrometry. The resolving power of conventional mass spectrometers is sufficient to separate all isotope signals, although expensive instruments and skill are required to eliminate interferences from molecules and polyatomic cluster ions. 

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