Selected ion flow tube mass spectrometry (SIFT-MS) is a chromatography-free, direct-analysis technique that is ideally suited to real-time, quantitative analysis of volatile compounds in air at trace concentrations. SIFT-MS utilises highly controlled, soft chemical ionisation – in the form of gas-phase ion–molecule reactions – coupled with mass spectrometry detection to provide both broad-spectrum and specific analysis of volatiles with diverse functionalities. This book provides readers with a broad understanding of the principles of the SIFT-MS technique and how it differs from conventional chromatographic approaches that are used for analysis of volatiles. It will also aid users to identify existing and new methods where adoption of SIFT-MS would be advantageous, e.g. through reduction in sample preparation or higher throughput, and provides the knowledge and insight required to develop best-practice methods and effectively evaluate the data that they generate and approaches to optimising, validating, and transferring methods to routine analysis and other applications. This book addresses two needs for SIFT-MS users: As a reference work, it gathers the fundamental principles from the literature and laboratory experience to provide a practical textbook for those using SIFT-MS in routine laboratories, research organisations and academia. It utilises a procedure-based approach to apply principles to routine analysis, simplifying implementation in routine analysis laboratories, while also accelerating effective application in other specialisations. The audience for this book is method developers and laboratory technicians engaged in routine analysis and research laboratories, but it is also well suited to graduate students, reducing the mentoring load for academics and research fellows.