IntechOpen is the world's leading publisher of open access books, with 7,200 open access books available, 191,000 international authors and editors, and 210 million downloads. The publisher emphasizes scientific research and collaboration, with authors from 154 countries, many of whom are top scientists. The books are indexed in the Web of Science Book Citation Index, and the publisher welcomes inquiries via book.department@intechopen.com. The chapter discusses the main ionisation techniques in mass spectrometry and the analysis of resulting fragments. It explains fundamental concepts such as mass spectrometry, isotopic percentages, nominal mass calculation, and fragmentation mechanisms. It also covers ionisation energy, ionisation voltage, and energy balance. The chapter highlights key milestones in both theoretical and experimental mass spectrometry, and discusses molecular fragmentation for various organic compounds, including alkanes, alcohols, phenols, ethers, carbonyl compounds, and others. Fragmentation schemes are followed by simplified spectra to aid understanding. The chapter concludes with a discussion on mass spectrum acquisition. Mass spectrometry is a destructive method used to measure molecular weight and provide data on molecular structure. It differs from other methods in that the sample is ionised and not subject to electromagnetic radiation. Ionised compounds are excited, inducing fragmentation. Analysis of such fragments provides information on the structure of molecules. Each fragment is characterised by the mass-to-charge ratio, m/z, and devices are able to separate and detect such ions. Mass spectrometers consist of three parts: the source, the dispersion system, and the detector. The chapter discusses various ionisation methods, including electron impact (EI), chemical ionisation (CI), electrospray ionisation (ESI), fast atom bombardment (FAB), field desorption ionisation, and MALDI. Each method has its own characteristics and applications. The chapter also covers the interpretation of mass spectra, including the nitrogen rule, isotopic abundance, and molecular formula determination. It discusses fragmentation mechanisms, energy aspects, and processes under electronic ionisation conditions. The chapter provides examples of mass spectra for various organic compounds, including alkanes, alkenes, arenes, halogenated compounds, hydroxy compounds, ethers, and carbonyl compounds. It also covers qualitative and quantitative analysis, as well as the interpretation of mass spectra for the main classes of organic compounds.IntechOpen is the world's leading publisher of open access books, with 7,200 open access books available, 191,000 international authors and editors, and 210 million downloads. The publisher emphasizes scientific research and collaboration, with authors from 154 countries, many of whom are top scientists. The books are indexed in the Web of Science Book Citation Index, and the publisher welcomes inquiries via book.department@intechopen.com. The chapter discusses the main ionisation techniques in mass spectrometry and the analysis of resulting fragments. It explains fundamental concepts such as mass spectrometry, isotopic percentages, nominal mass calculation, and fragmentation mechanisms. It also covers ionisation energy, ionisation voltage, and energy balance. The chapter highlights key milestones in both theoretical and experimental mass spectrometry, and discusses molecular fragmentation for various organic compounds, including alkanes, alcohols, phenols, ethers, carbonyl compounds, and others. Fragmentation schemes are followed by simplified spectra to aid understanding. The chapter concludes with a discussion on mass spectrum acquisition. Mass spectrometry is a destructive method used to measure molecular weight and provide data on molecular structure. It differs from other methods in that the sample is ionised and not subject to electromagnetic radiation. Ionised compounds are excited, inducing fragmentation. Analysis of such fragments provides information on the structure of molecules. Each fragment is characterised by the mass-to-charge ratio, m/z, and devices are able to separate and detect such ions. Mass spectrometers consist of three parts: the source, the dispersion system, and the detector. The chapter discusses various ionisation methods, including electron impact (EI), chemical ionisation (CI), electrospray ionisation (ESI), fast atom bombardment (FAB), field desorption ionisation, and MALDI. Each method has its own characteristics and applications. The chapter also covers the interpretation of mass spectra, including the nitrogen rule, isotopic abundance, and molecular formula determination. It discusses fragmentation mechanisms, energy aspects, and processes under electronic ionisation conditions. The chapter provides examples of mass spectra for various organic compounds, including alkanes, alkenes, arenes, halogenated compounds, hydroxy compounds, ethers, and carbonyl compounds. It also covers qualitative and quantitative analysis, as well as the interpretation of mass spectra for the main classes of organic compounds.