Applications of ambient mass spectrometry of natural products in the fields of food safety, phytochemistry and forensics

Ambient mass spectrometry is a relatively new versatile tool in the natural product chemist's toolbox. It allows sampling of the surface of an object on your benchtop under ambient conditions and often without any sample preparation. The possibilities and limitations of ambient MS are discussed and illustrated by several applications from the authors' lab. Direct spray MS is the simplest and cheapest form of ambient MS, requiring only a high voltage supply and a mass spectrometer. It allows the probing of the surface chemicals of any hard spiked material. In a food safety example, a neurotoxin could be identified in seconds [1]. With Laser Ablation Electrospray Ionization Mass Spectrometry (LAESI-MS), it is possible to obtain 2 or even 3-dimensional images of any ionizable constituent on or just below the surface of for instance a fresh flower or leaf. Both targeted and untargeted analyses are possible. The untargeted analysis of the tip cap of a maize kernel is shown, leading to the identification of highly localised N,N-bis-coumaroyl spermidine [2]. Direct Analysis in Real Time Mass Spectrometry (DART-MS) is an easy to handle, sensitive and fast technique allowing analysis of many natural products without any extraction or sample preparation. With an internal standard semi-quantitative measurements of secondary plant metabolites are possible. If the object to be analysed is moved in front of the DART outlet, spatial information can be obtained. An example of the latter is in the hair forensics field. The detection of Δ-9-tetrahydrocannabinol (THC), cocaine and many synthetic drugs of abuse along a hair proved possible with DART-MS [3,4]. All in all ambient MS is a promising technique applicable in many different fields such quality control of herbal drugs, food safety, plant pathology, chemical ecology, metabolomics, adulteration detection, and imaging.

Keywords: ambient MS, direct spray, LAESI, imaging MS, DART, forensics.

References:

[1] Schrage M, Shen Y, Zuilhof H, Nielen MWF, van Beek TA, Chen B. Rapid and simple neurotoxin-based distinction of Chinese and Japanese star anise by direct plant spray mass spectrometry. J Chromatogr A 2013; 1317: 246 – 253

[2] Nielen MWF, van Beek, TA. Macroscopic and microscopic spatially-resolved analysis of food contaminants and constituents using Laser Ablation Electrospray Ionization Imaging Mass Spectrometry. Anal Bioanal Chem 2014; 406: 6805 – 6815

[3] Duvivier WF, van Beek TA, Pennings E, Nielen MWF. Rapid analysis of THC in hair using direct analysis in real time ambient ionization orbitrap mass spectrometry. Rapid Commun Mass Spectrom 2014; 28: 682 – 690

[4] Duvivier WF, van Putten MR, van Beek TA, Nielen MWF. (Un)targeted scanning of locks of hair for drugs of abuse by direct analysis in real time-high-resolution mass spectrometry. Anal Chem 2016; 88: 2489-2496