High-resolution mass spectrometry in food and environmental analysis.

Abstract

In 1968 Finnigan introduced the first commercial quadrupole mass spectrometer equipped with a computerized dataprocessing unit. Since then, the coupling of gas chromatography to mass spectrometry (GC–MS) for the analysis of contaminants in environmental and biological samples has achieved impressive success, and at the end of the last millennium it was in routine use in many laboratories. Furthermore, GC–MS was used to determine food composition, and thus it was a tool to guarantee food authenticity and safety while also providing information about the nutritional value. The discovery of atmospheric-pressure ion sources during the mid-80s was another important development, because it made the effective coupling of high-performance liquid chromatography (HPLC) to MS possible. With this technique available, the analysis of low-volatility and thermolabile compounds became possible without the need for a long derivatization procedure, which was sometimes difficult to perform and not always successful. However, after the initial excitement, the limitations of the technique soon became evident; these result from the relatively low efficiency of HPLC compared with GC and the large number of compounds present in samples that can interfere with the determination of the analytes of interest. Therefore, the need for higher MS selectivity was soon realized by the research community. The technology to overcome this problem was fortunately already available. Collision-induced dissociation (CID) was introduced by Jennings and McLafferty at end of the 60s; tandem MS (MS–MS) was made possible with the triplestage quadrupole (QqQ) introduced by Yost, Henke, andMorrison at end of the 70s; and finally multi-stage MS was provided by the Paul ion trap, patented in 1953. The addition of one more dimension in separation greatly increased selectivity; furthermore, rapid advances were made toward the design of mass spectrometers with improved sensitivity, in parallel with advances in separation technology and the development of columns with improved efficiency. Currently, HPLC and ultra HPLC (UHPLC) coupled to QqQ working in selectedreaction-monitoring (SRM) mode are the most widespread techniques in both environmental and food analysis because they provide the analyst with a high degree of selectivity and sensitivity. Hence, complex and labor-intensive sample-processing techniques could be substantially simplified. However, the use of SRM mode on QqQ instruments proved to have some limitations, including a limit to the number of compounds monitored per analysis, the inability to screen for unknowns, and the reliance on reference standards. To overcome these limitations, there is a need for an alternative approach using instruments capable of providing full spectral information and high mass resolution and mass accuracy. Classic high-resolution (HR) mass spectrometers, for example double-focus sector or Fourier-transform ion cyclotron resonance (FT-ICR), were too slow, complex to handle, and expensive to buy and to maintain. However, the introduction of modern time-of-flight (TOF) and electrostatic FT trap (Orbitrap) instrumentation totally changed the situation. TOF and Orbitrap have undergone tremendous technological advances giving—in addition to improved mass resolution, accuracy, and sensitivity—fast scan velocity, sufficient dynamic range, and the possibility of MS–MS when part of hybrid instruments. Because of their unrivaled resolution, modern FT-ICR mass spectrometers also have their advocates in the Published in the topical collectionHigh-Resolution Mass Spectrometry in Food and Environmental Analysis with guest editor Aldo Lagana.