Liquid Chromatography-Mass Spectrometry

Abstract

One of the analytical challenges posed by forensic science includes the identification and quantification of complex mixtures containing known, unknown, and suspect compounds within complex matrices. Ultra- and high-performance liquid chromatography(UPLC and HPLC) coupled with soft ionization techniques(e.g., electrospray ionization (ESI) or atmospheric pressure chemical ionization; APCI), along with low-resolution(triple quadrupoles and ion trap) and high-resolution (e.g., quadrupole-time of flight, Orbitrap, and Fourier transform ion cyclotron resonance) mass spectrometers, have significantly progressed the molecular-level characterization of complex drugs, metabolites, macrobiomolecules, and synthetic chemicals. In the past, gas chromatography (GC) coupled with mass spectrometry (MS) was recognized as one of the primary analytical techniques used in forensic laboratories. GC–MS was widely used for analysis of illegal substances in body fluids, testing fibers and blood from a crime scene, and detection of explosive residues.However, GC–MS-based techniques often require extensive sample cleanup and, for the analysis of polar compounds, the routine application of derivatization procedures. These limitations have been overcome by the advent of LC–MS-based techniques. Moreover, the urgency in developing fast and reliable analytical methods with minimal sample preparation has driven solid-phase extraction (SPE) media and column manufacturers to offer a new means of rapidly and effectively cleaning up and injecting samples into mass spectrometers. Ionization sources, sample preparation techniques, emerging injection methods, matrix effects, and state-of-the-art LC–MS instrumentation are critically discussed in the following sections, along with the examples of applications to forensic science taken from the scientific literature. Throughout this article, HPLC is used interchangeably with LC.