Thompson mass spectrometer

In its simplest form, a mass spectrometer is an instmment that measures the mass-to-charge ratios ml of ions formed when a sample is ionized by one of a number of different ionization methods (1). If some of the sample molecules are singly ionized and reach the ion detector without fragmenting, then the ml ratio of these ions gives a direct measurement of the molecular weight. The first instmment for positive ray analysis was built by Thompson (2) in 1913 to show the existence of isotopic forms of the stable elements. Later, mass spectrometers were used for precision measurements of ionic mass and abundances (3,4). 

Historical That positive rays could be deflected in electric and magnetic fields was shown as early as 1898 by Wien, but it was not until 1912 that what was to become the forerunner of the modem mass spectrometers was built by JJ. Thompson, who became known as the father of mass spectrometry. The existence of two isotopes of neon (m/e 20 and 22) was demonstrated by Thompson with this instrument. The discovery of stable isotopes of elements has been generally considered the... 

Griest, W. H. Wise, M. B. Hart, K. I Lammert, S. A. Thompson, C. V. Vass, A. A. Biological agent detection and identification by the Block II chemical biological mass spectrometer. Field Anal. Chem. Technol. 2001, 5,177-184. 

The mass spectrometer was developed by J.J. Thompson. In obtaining the mass spectrum of neon, he found a large signal at 20 amu, but also a small signal at 22 amu. He first assumed it was an impurity. So, he kept repeating the experiment, each time more and more carefully purifying the sample, but the small signal at 22 amu remained constant. What Thompson discovered was the existence of isotopes. Isotopes have the same atomic number but different mass number (same Z, different A), or the same number of protons and different number of neutrons. 

As well, mass spectrometers can find the relative abundance of each isotope in an element. In 1912, J.J. Thompson first detected neon-20 and neon-22 in a sample of neon gas by using a magnetic field to separate the isotopes. 

The measurement of isotopic abundances began early this century following the discovery of neon isotopes by J.J. Thompson in 1912. F.W. Aston developed the mass spectrometer into a quantitative instrument for measuring isotopic abundances and by 1935 the isotopic composition of most elements was known. The first International Table of Stable Isotopes was drawn up in 1936, while the latest table of Isotopic Compositions of the Elements appeared recently (4). Lead is an element for which there was early evidence of natural variations in its isotopic composition (5) these were ultimately used to measure the age of the Earth (6). Natural variations have been reported in 43 other elements although many relate to exceptional samples. There are 18 elements in which variations are not uncommon, although most of these elements have relatively light atoms with atomic numbers less than 16 (4). 

Mass spectrometry is a well-established technique J.J. Thompson designed the first mass spectrometer in 1912. The methods for ion production in these early times were limited to gaseous samples (or low vapor pressure molecules) for analytical... 

Thome FA, Heavner DL, Ingebrethsen BJ, Eudy LW, Green CR (1986) Environmental tobacco smoke monitoring with an atmospheric pressure chemical ionization mass spectrometer/mass spectrometer coupled to a test chamber. Proc 79th Annual Meet Air Pollution Control Assoc. Air Pollution Control Assoc, Pittsburgh, paper 86-37.6 Thompson CV, Jenkins RA, Higgins CE (1989) A thermal desorption method for the determination of nicotine in indoor environments. Environ Sci Technol 23 429-435 Thomson BA, Davidson WR, Lovett AM (1980) Applications of a versatile technique for trace analysis atmospheric pressure negative chemical ionization. Environ Health Perspect 36 77-84... 

An alternative method of filtering is based on the use of a magnetic field. Magnetic mass spectrometers were developed and improved by the fathers of mass spectrometry, Thompson, Aston, and Bainbridge, in the early part of the twentieth century. An ion with velocity v travelling in a perpendicular magnetic field of flux density B will follow a circular trajectory of radius r. 

Isotopes are atomic species of the same element that differ in atomic mass that is, nuclei with a given number of protons but differing numbers of neutrons. The term isotope was first used by Soddy in 1913, the same year in which the existence of naturally occurring isotopes was first reported by J.J. Thompson, who discovered two stable isotopes of neon (mass 20 and 22) using one of the earliest mass spectrometers. Today, a range of isotopes has been discovered or made for every known element, the vast majority being made by nuclear reactions using man-made sources of nucleons. 

After J. J. Thompson used a mass spectrometer to separate atomic isotopes in 1913, MS was slowly developed and improved as an analytical tool. It proved to be powerful for identifying unknown compounds, as well as elucidating structures of both inorganic and organic compounds. It was widely used for the characterization of petroleum products and probably would have grown even more dramatically if GC had not been introduced in 1952. 

Kim, T.Y., Thompson, M.S., and Reilly, J.P. (2005) Peptide photodissodation at 157nm in a linear ion trap mass spectrometer. Rapid Commun. Mass Spectrom., 19,1657-1665. 

Thompson, X, Worthington, T. (2004) The proton transfer reaction mass spectrometer and its use in the medical sciences applications to drug assays and the monitoring of bacteria. International Journal of Mass Spectrometry, 239, 235-241. 

Shevchenko, A. Chemushevich, I.V. Ens, W. Standing, K.G. Thompson, B. Wilm, M. Mann, M. Rapid De Novo Peptide Sequencing by a Combination of Nanoelectrospray, Isotopic Labeling and a Quadrupole/Time-of-Flight Mass Spectrometer. Rapid Commun. Mass Spectrom. 1997,11, 1015-1024. 

Thompson, J. J. and R. S. Houk. 1986. Inductively coupled plasma mass spectromet-ric detection for multielement flow injection analysis and elemental speciation by reversed-phase liquid chromatography. Anal. Chem. 1986 2541-2548. 

Acknowledgments. We thank Dr. Robert Fairweather and Marvin Thompson for their help in operating the mass spectrometer. This work was supported by PHS grants NS 11716, NS 12482, and MH 27158. 

Inductively Coupled Plasma-Mass Spectrometry (ICPMS), A major advance in analyses of both lead concentrations and isotopic compositions has been the development of ICPMS. Since the first commercial instrument was introduced in 1983 (Houk and Thompson 1988), this method has rapidly assumed a prominent position in many research laboratories (e.g., Barnes 1991 Hieftje and Vickers 1989). Inductively coupled plasma-mass spectrometers, in which the sample is introduced into a plasma with excitation temperatures (> 5000°K) that efficiently atomize and ionize lead into a mass spectrometer (quadrapole or magnetic sector), are becoming relatively inexpensive and efficient alternatives to TIMS and other established methods (AAS, XRFA, ASV, ICP-AES) (Barnes 1991 Delves and Campbell 1988). 

The physicist J.J. Thompson developed the first mass spectrometer and proved for the first time the existence of isotopes ( °Ne and Ne). He wrote in his book Rays of Positive Electricity and their Application to Chemical Analysis I have described at some length the application of positive rays to chemical analysis one of the main reasons for writing this book was the hope that it might induce others, and especially chemists, to try this method of analysis. I feel sure that there are many problems in chemistry which could be solved with far greater ease by this than any other method . Cambridge 1913. In fact, Thompson developed the first isotope ratio mass spectrometer (IRMS). 

Aston continued the work of Thompson with his own mass spectrometer equipped with a photoplate as detector. The results verified the existence of isotopes of stable elements (e.g. Cl and Cl) and confirmed the results of Thompson. 

Plate 27 Portrait of Francis Aston (1877-1945) British physicist and Nobel Laureate. After WWl, Aston helped Thompson in his studies of the deflection of ions in magnetic fields. He went on to improve Thompson s apparatus, designing it so as to make all atoms of a given mass fall on the same part of a photographic plate. Working with neon, he found that two lines were isotopes. He repeated this with chlorine with similar results. The device, called the mass spectrometer, showed that most stable elements had isotopes. His work earned him the 1922 Nobel Prize for Chemistry, and introduced a powerful new analytical tool to science. See Mass Spectrometry, Historical Perspective. Reproduced with permision from Science Photo Library. 

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