Chapter 1
Introduction of Mass Spectrometry and Ambient Ionization Techniques

Yiyang Dong, Jiahui Liu and Tianyang Guo

College of Life Science & Technology, Beijing University of Chemical Technology, No. 15 Beisanhuan East Road, Chaoyang District, Beijing, 100029, China

1.1 Evolution of Analytical Chemistry and Its Challenges in the Twenty-First Century

The Chemical Revolution began in the eighteenth century, with the work of French chemist Antoine Lavoisier (1743-1794) representing a fundamental watershed that separated the "modern chemistry" era from the "protochemistry" era (Figure 1.1). However, analytical chemistry, a subdiscipline of chemistry, is an ancient science and its metrological tools, basic applications, and analytical processes can be dated back to early recorded history [1]. In chronological spans covering ancient times, the middle ages, the era of the nineteenth century, and the three chemical revolutionary periods, analytical chemistry has successfully evolved from the verge of the nineteenth century to modern and contemporary times, characterized by its versatile traits and unprecedented challenges in the twenty-first century.

Figure 1.1 Portrait of Antoine-Laurent Lavoisier and his wife by Jacques-Louis David, about 1788.

Historically, analytical chemistry can be termed as the mother of chemistry, as the nature and the composition of materials are always needed to be identified first for specific utilizations subsequently; therefore, the development of analytical chemistry has always been ahead of general chemistry [2]. During pre-Hellenistic times when chemistry did not exist as a science, various analytical processes, for example, qualitative touchstone method and quantitative fire-assay or cupellation scheme have been in existence as routine quality control measures for the purpose of noble goods authentication and anti-counterfeiting practices. Because of the unavailability of archeological clues for origin tracing, the chemical balance and the weights, as stated in the earliest documents ever found, was supposed to have been used only by the Gods [3].

During the middle ages (fifth to fifteenth century), alchemists began to assemble scattered knowledge that later became chemistry. Wet chemistry using mineral acids with noble metals symbolized the beginning of analytical chemistry as we know it today, and the evolution continued during the Age of Medicinal Chemistry (AD 1500-1650) as well as during the phlogiston era. The phlogiston theory was developed by J.J. Becher (1635-1682) late in the seventeenth century and was extended and popularized by G.E. Stahl (1659-1734). Some classical analytical methods had been developed since the seventeenth century: gravimetric analysis was invented by Friedrich Hoffmann (1660-1742), titrimetric analysis using nature dye indicators was widely practiced in 1874. Guy-Lussac (1778-1850) developed a titrimetric method for silver and got remarkable accuracy better than 0.05%, and Antoine Lavoisier who used balance to confute the phlogiston theory, demonstrated the law of mass conservation, which earned him the title "father of quantitative analysis."

In 1826, Jean-Baptiste Dumas (1800-1884) devised a method for the quantitative determination of nitrogen in chemical substances. In 1860, the first instrumental analysis, namely, flame emissive spectrometry was developed by Robert Bunsen and Gustav Kirchhoff (Figure 1.2) who discovered rubidium (Rb) and caesium (Cs), and up to the latter half of the nineteenth century, about 90 elements were successfully discovered by the support of analytical chemistry, from which organic chemistry has benefited a lot. The periodic table of elements was created by Dmitri Mendeleev (1834-1907) in 1869. In 1876, the paper entitled "On the Equilibrium of Heterogeneous Substances" published by Willard Gibbs (1839-1903) introduced and developed systematic chemical concepts as cornerstones and fundamental principles for analytical chemistry.

Figure 1.2 Photograph of Robert Bunsen (right) and Gustav Kirchhoff (left).

The year 1894 was very significant when Wilhelm Ostwald (1853-1932) published an important and very influential text on the scientific fundamentals of analytical chemistry entitled "Die Wissenschaftichen Grundlagen der Analytischen Chemie" (Figure 1.3). In addition, a series of chemical revolutions, that is, the first chemical revolution at the molar level from 1770-1790, the second chemical revolution at the molecular level from 1855-1875, and the third chemical revolution at the electrical level from 1904-1924, were chronologically implemented, which greatly facilitated the emergence and bloom of modern analytical chemistry, via which instrumental analysis became prevalent to address assorted analytical needs [4].

Figure 1.3 Wilhelm Ostwald (1853-1932). Recipient of the 1909 Nobel Prize for Chemistry "in recognition of his work on catalysis and for his investigations into the fundamental principles governing chemical equilibria and rates of reaction."

A prototype of mass spectrometer for ion separation and identification was invented by English physicist and 1906 Nobel Laureate in Physics Joseph John Thomson (1856-1940) at the beginning of the twentieth century, and in 1922, Francis William Aston (1877-1945) at the Cavendish laboratory in the University of Cambridge won the Nobel Prize for Chemistry for his investigation of isotopes and atomic weights using developed mass spectrometer with improved mass resolving power and mass accuracy. The spectrometer was developed in 1941, and self-recording Infrared, direct-reading, and self-recording emission spectrophotometers appeared in 1951. Gas chromatographs (GC) and nuclear magnetic resonance (NMR) spectrometers were produced in 1953, and the 1959 Nobel Prize for Chemistry was awarded to Heyrovsky for the invention of polarography. Around 1960, atomic absorption spectroscopy (AAS) was developed and GC coupled with mass spectrometry (MS) was applied for the identification of organic compounds. Later in the 1970s, high performance liquid chromatography (HPLC), with the merits of linking to MS with established analyte ionization strategies, emerged as a powerful tool to meet analytical challenges especially for natural product and biomedical researches.

Classical and modern chemistry with intellectual separation, identification, and quantitation strategies have been well studied and utilized to meet scientific, technical, and sometimes engineering needs; however, in the twenty-first century, due to rapid urbanization, mass industrialization, and business globalization, there are many serious problems, for example, resource shortage, climate change, and environment deterioration, facing the world, and therefore contemporary analytical chemistry needs to go further to deal with assorted eco-environmental, social public, macro-economic, or even individual ethical needs accordingly. Nowadays, micro-morphological imaging, visual identification, nontargeted profiling or multianalyte analysis, and ultra-sensitive, superior selective, high-throughput, in situ nondestructive and rapid cost-effective assay schemes are frequently needed for numerous analytical purposes, which are, to name a few, characterization of advanced materials, researches of noncovalent conjugates, discovery of therapeutic drugs, prognosis of new contagious diseases, surveillance of process or product quality, safeguarding food security and safety, management of consumer complaints, preservation of ecosystem, criminal investigations and forensic science, anti-terrorism practices, archeological excavations, and explorations of deep earth/sea and space missions. Therefore, to fulfill these challenging analytical assignments, contemporary analytical chemistry needs to interact intensively with its sister disciplines, for example, physics, electromechanics, biology, mathematics, and information science.

Probably the most challenging task in contemporary analytical chemistry lies in unveiling vital phenomena and life dynamics systematically using analytical tools developed for proteomics, metabolomics, and lipidomics researches. In addition, for analytes at the single molecular level or near zero concentrations where quantized nature of the matter dominates in its natural or complicated matrices, characterization of analysis capability and assurance of result fidelity continue to remain formidable tasks. As exemplified by the detection of persistent organic pollutant dioxins and polychlorinated biphenyls (PCBs) at part-per-trillion or part-per-quadrillion level, for geographical identification, or for botanical/zoological authentication of olive oils and honeys, where sophisticated sample pretreatment steps and advanced instrumentations with chemometrics or bioinformatics packages are usually needed to acquire large volume analytical information for further data mining and model prediction.

In practice, analytical chemistry is inherently a metrological science with conventional separation, identification, and quantitation procedures. In order to tackle all sorts of scientific, technical, and social problems, contemporary analytical chemistry has been evolved nowadays as an autonomous scientific discipline that develops and applies methods, instruments, and strategies to obtain information on the composition and nature of matter in space and time [5] (Figure...