Surface analysis by plasma assisted mass spectrometry – PLASPAMS

A cold plasma micro-jet will induced desorption of nonvolatile molecules on surfaces, to be further injected into the instrument, without degrading the surface as would other techniques. The instrument will consist of an ion source, a reaction chamber at high pressure and a mass analyzer. Another of the innovative parts of the project will be the use of the chemical ionization of molecules. A Micro-Hollow Cathode Discharge will be developed to produce the precursor ions. The reaction chamber will be of the type Ion Funnel. The mass analysis will be performed by a radio frequency trap, technology well adapted to the implementation of the MS / MS, and well adapted to miniaturization.

To date the public results of the program are as follows. A Micro-Hollow Cathode Discharge operated stably in a mixture of argon and water vapor to create cold plasma as a potential source of hydronium ions. Stable operation was obtained for a very low carrier gas stream of steam, and a higher ion current was measured for the air compared to argon. The effects of the flow of argon gas on the spatiotemporal distribution of the plasma in the micro-jet were highlighted. A desorption bibenzil molecules deposited on a glass plate, by a micro-jet of argon plasma, was achieved without fragmentation of the molecules.

The program is progressing according to the project originally proposed.

8th International Workshop on Microplasmas (11-15 mai 2015, Newark, NJ, USA).
A Micro-Hollow Cathode Discharge in argon-water vapour mixtures.
G. Bauville, S. Pasquiers, J. Santos Sousa.

19th International Conference on Atomic Processes in Plasmas (4- 8 avril 2016, Paris, France).
Argon metastable density in an atmospheric microplasma jet in interaction with a dielectric surface.
Et. Es-Sebbar, K. Gazeli, G. Bauville, M. Fleury, O. Neveu, S. Pasquiers , V. Puech, J. Santos Sousa.

64th Conference of the American Society for mass Spectrometry (5-9 juin 2016, San Antonio, TX, USA).
Development of a drift tube mass spectrometer associated with plasma microjets.
J. Lemaire, B. Brahim, M. Heninger, E. Louarn, H. Mestdagh, G. Bauville, N. Blin-Simiand, Et-T. Es-Sebbar, M. Fleury, S. Pasquiers, J. Santos Sousa, E. Bauchard, J. Leprovost.

Impact of an atmospheric argon plasma jet on a dielectric surface and desorption of organic molecules.
X. Damany, S. Pasquiers, N. Blin-Simiand, G. Bauville, B. Bournonville, M. Fleury, P. Jeanney, J. Santos Sousa.
The European Physical Journal: Applied Physics, DOI : 10.1051/epjap/2016150594 (2016).

This project aims at the detection and accurate identification of compounds present on surfaces at trace level by combining mass spectrometry with chemical ionization to determine the molecular signatures and desorption by plasma microjets to get in the gas phase the substances present on the surface to be analyzed. The key points are the high throughput analysis enabled by mass spectrometry, the preservation of the molecular information with chemical ionization and get the prohibited substances in the gas phase with the cold plasma jet without damaging surfaces.
The project is in the thematic "rupture in safety research" as well as in the thematic "protection of citizens and infrastructure" as the ability to detect and identify with high sensitivity the compounds present at trace concentration on surfaces can be a key element to detect malicious actions, and will help in the fight against crime, terrorism and drug trafficking. It is often difficult, after handling prohibited substances such as explosives or narcotics, not to leave some marks on surfaces. The low volatility of these substances makes them difficult to detect but also ensures they remain present long enough.
In order to achieve its goal our associates three teams : one team specialized in generation and characterization of cold plasmas, another one specialized in ion chemistry and in experimental development in mass spectrometry and a start-up already selling high performance spectrometers and a flash thermal desorption concentrator.
One objective of the project is the optimization of the different parts of the analytical chain (Sampling, ionization mode and mass analysis) to achieve an accurate and sensitive compact instrument.
The sampling method is crucial. The advantages of cold plasma microjets to achieve a soft desorption with a low energy expense make their use in analysis growing very fast. Our system will allow fast analysis of compounds deposited on surfaces.
The ionization method should not destroy the molecular information by a too brutal technique. Chemical ionization is soft and ionizes the molecules without dissociating them. Moreover it ionize specifically the analytes without ionizing the main constituent of the air carrier and this is essential to have a good sensitivity.
An original ion source will be developed for the production of precursor ions based on a MHCD (Micro Hollow Cathode Discharge). The reaction with the sample gas will take place under conditions of pressure and renewal ensuring a good sensitivity and fast time response. A RF device will ensure a good transmission of the ions produced by chemical ionization.
The analysis should identify precisely the prohibited substances, without risk of false detection. For this purpose the nominal mass is not a sufficient information since different molecules can have the same nominal mass. Exact mass measurement is a way to accurately identify and differentiate molecules different chemical formulas. But the "high resolution" mass spectrometers are not amenable to miniaturization. This is why will use in this project a mass analyzer based on a radiofrequency trap in which we will implement the fragmentation of mass selected ions (MS / MS technique) in order to identify precisely the molecules.