Orbitrap Mass Spectrometry: Evolution and Applicability

Mass spectrometry is an extremely valuable analytical tool. In particular, food, environmental, forensic and anti-doping laboratories greatly benefit from the powerful and sensitive instrumentation used today. According to Martins et al. (2016), over time, the demand for more precise instrumentation and the need to overcome obstacles in detection and quantification has given rise to instruments capable of atmospheric ionization techniques such as electrospray (ESI) and atmospheric pressure chemical ionization (APCI).

One of the greatest achievements is the combination of high-resolution mass spectrometry and liquid chromatography (LC-HRAM MS) found in Orbitrap mass spectrometry (Orbitrap-MS) developed by Thermo Fisher Scientific. This method provides increased selectivity and is ideal for studying complex mixtures. As the authors further explain, the mass resolving power of the latest Orbitrap instrument can, in fact, reach up to 450,000 FWHM at m/z 200 with <3 ppm mass accuracy with external calibration.

This power and accuracy are possible because of the fundamentally different ion detection mechanism used in Orbitrap mass spectrometers. In fact frequencies of ion oscilations are measured with high accuracy, compared to other techniques using measurement of flight times or electric currents.This difference sets Orbitrap MS apart from beam-type analyzers such as Time of Flight (TOF), magnetic sector and quadrupole which rely on ion statistics. As a result, the Orbitrap requires fewer ion detections to achieve the same mass accuracy, even when coupled to liquid or gas chromatographic separation techniques.

The Orbitrap family of mass spectrometers contains three main players: the LTQ Orbitrap, the Orbitrap Fusion, and the Exactive. Since the release of the very first LTQ Orbitrap (Classic), in 2005, these three players continue to evolve and improve with new features and updated hardware.

The Exactive family of mass spectrometers is a preferred choice in environmental, food, antidoping and forensic laboratories. In particular, the Q Exactive benchtop instrument is a flexible, high performing tool for both research and routine workflows. The Q Exactive has a mass resolving power up to 140,000 FWHM at m/z 200 and is ideal for quantifying compounds.

The authors describe four valuable Q Exactive, workflows for identifying and quantifying compounds of interest:

1. Full scan combined with data-dependent MS/MS (FS/ddMS2)
2. Full scan combined with data-independent analysis (FS/DIA)
3. Targeted single ion monitoring with data-dependent MS/MS (t-SIM/ddMS2)
4. Parallel reaction monitoring

The Orbitrap family of mass spectrometers has already greatly expanded since its humble beginnings 11 years. The authors predict future developments, including more streamlined workflows, will further enhance the capabilities and push the limits of mass spectrometry.

Reference:

Martins, C.P.B., et al. “Orbitrap Mass Spectrometry: Evolution and Applicability”, Comprehensive Analytical Chemistry, Applications of Time-of-Flight and Orbitrap Mass Spectrometry in Environmental, Food, Doping, and Forensic Analysis 2016 (71) (pp. 3-18)