The identification of unknown molecules has been one of the cornerstone applications of mass spectrometry for decades. This tutorial reviews the basics of the interpretation of electrospray ionization‐based MS and MS/MS spectra in order to identify small‐molecule analytes (typically below 2000 Da). Most of what is discussed in this tutorial also applies to other atmospheric pressure ionization methods like atmospheric pressure chemical/photoionization. We focus primarily on the fundamental steps of MS‐based structural elucidation of individual unknown compounds, rather than describing strategies for large‐scale identification in complex samples. We critically discuss topics like the detection of protonated and deprotonated ions ([M + H]⁺ and [M − H]⁻) as well as other adduct ions, the determination of the molecular formula, and provide some basic rules on the interpretation of product ion spectra. Our tutorial focuses primarily on the fundamental steps of MS‐based structural elucidation of individual unknown compounds (eg, contaminants in chemical production, pharmacological alteration of drugs), rather than describing strategies for large‐scale identification in complex samples. This tutorial also discusses strategies to obtain useful orthogonal information (UV/Vis, H/D exchange, chemical derivatization, etc) and offers an overview of the different informatics tools and approaches that can be used for structural elucidation of small molecules. It is primarily intended for beginning mass spectrometrists and researchers from other mass spectrometry sub‐disciplines that want to get acquainted with structural elucidation are interested in some practical tips and tricks.

中文翻译：

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通过电喷雾电离质谱鉴定小分子的教程：结构阐明的实用技术

数十年来，未知分子的鉴定一直是质谱技术的基础应用之一。本教程回顾了基于电喷雾电离的MS和MS / MS光谱解释的基础知识，以识别小分子分析物（通常低于2000 Da）。本教程中讨论的大多数内容也适用于其他大气压电离方法，例如大气压化学/光电离。我们主要关注单个未知化合物的基于MS的结构阐明的基本步骤，而不是描述复杂样品中大规模鉴定的策略。我们批判性地讨论了诸如质子和去质子离子（[M + H] ⁺和[M-H] ^-）以及其他加成离子，确定分子式，并为产物离子光谱的解释提供一些基本规则。我们的教程主要关注单个未知化合物（例如，化学生产中的污染物，药物的药理学改变）基于MS的结构阐明的基本步骤，而不是描述复杂样品中大规模鉴定的策略。本教程还讨论了获取有用的正交信息（UV / Vis，H / D交换，化学衍生化等）的策略，并概述了可用于小分子结构解析的各种信息学工具和方法。