Evolution and Developments of Proton Transfer Reaction-Mass Spectrometry for Security Applications

1. Evolution and Developments of Proton Transfer Reaction-Mass Spectrometry for Security Applications Spectrometry for Security Applications– First International Workshop Dr. Ramón González-Méndez MRSC Head Laboratory Technician | Centre for Agroecology, Water and Resilience | Coventry University | E: Ramon.Gonzalez-Mendez@coventry.ac.uk Honorary Research Associate | Molecular Physics Research Group |University of Birmingham  | E: R.GonzalezMendez@bham.ac.uk Dornbirn 11th February 2019

2. OVERVIEW Spectrometry for Security Applications– First International Workshop • PROTON TRANSFER REACTION-MASS SPECTROMETRY (PTR-MS). Fundamentals and application to explosive compounds • DEVELOPMENT OF NEW METHODOLOGIES FOR IMPROVED COMPOUND SELECTIVITY (AND SENSITIVITY): • Use of a radio frequency ion-funnel (RFIF) drift tube • Rapid reduced electric field (E/N) switching • Applications to the Detection of Pre-blast Smokeless Powder Organic Additives • CONCLUSIONS • Combining bothsimultaneously Dornbirn 11th February 2019

3. PTR-MS: Fundamentals Spectrometry for Security Applications– First International Workshop Proton transfer reaction mass spectrometry (PTR-MS) involves: H3O+ + M → MH+ + H2O , if PA (M) > PA (H2O) Use of O2+ as reagent gas  Soft Chemical Ionisation-Mass Spectrometry (SCIMS) • To avoid excessive formation of ions clusters, such as H3O+(H2O), this chemistry is performed under mildly energetic collision-induced dissociation (CID) conditions by applying an electric field across the reaction zone (drift tube). • The CID conditions are defined by the reduced electric field, E/N, where E is the electric and N is the number density of neutral gas in the drift tube (usually air). Dornbirn 11th February 2019

4. PTR-MS: Fundamentals Spectrometry for Security Applications– First International Workshop Red colour represents the ions trajectories from the inlet to the detector H3O+ made here H3O+ + M → MH+ + H2O Dornbirn 11th February 2019

5. PTR-MS: Fundamentals Spectrometry for Security Applications– First International Workshop The drift tube (DT) is the heart of the instrument PTR-MS Dornbirn 11th February 2019

6. PTR-MS: Fundamentals Spectrometry for Security Applications– First International Workshop • Advantages (relevant for Security Applications( of the technique are: • Soft ionization = low fragmentation • Normal constituents of air are not ionisable • PTR-MS is selective to most organic compounds because of the favourable proton affinities • Real-time (time resolution  100msec) • No carrier gas necessary • No sample preparation needed (or minimum) Dornbirn 11th February 2019

7. PTR-MS: application to explosive compounds Spectrometry for Security Applications– First International Workshop One of my first works for PTR-MS and explosives detection: Showed as a first generation KORE PTR-ToF-MS instrument could achieve fast ng region detection with little carry-over effects Dornbirn 11th February 2019

8. PTR-MS: application to explosive compounds Spectrometry for Security Applications– First International Workshop Similar approach to Carl’s TEIS, but different operation mode Commercial PTFE swabs Dornbirn 11th February 2019

9. DEVELOPMENT OF NEW METHODOLOGIES FOR IMPROVED COMPOUND SELECTIVITY Spectrometry for Security Applications– First International Workshop • But high sensitivity is, in itself, not sufficient for trace explosive detection (false positives/negatives). • High selectivity is also required so that chemical compounds can be identified with • high levels of confidence in real-time and trace quantities. • In the context of PTR-MS, specificity enhancement can be achieved by • manipulating the ion−molecule chemistry in a controlled way through collisional induced dissociation processes. We explored two ways : • 1- Use of a RFIF drift tube • 2-Rapid reduced electric field (E/N) switching • Combining both of them Dornbirn 11th February 2019

10. 1. KORE RADIO FREQUENCY ION FUNNEL DRIFT TUBE-PTR-MS. What it is? Spectrometry for Security Applications– First International Workshop • Originally developed to improve sensitivity • focussing ions radially and “forcing” them to go • through the reactor exit aperture and into the • mass spectrometer region. More ions into the • MS and thus higher sensitivity. • The DC field drives ions forward • Rffield focuses ions radially • Diverging ion trajectories mean the ions • encounter the RF field and 'slide down' the • funnel wall Operating conditions • Frequency  760 kHz, • Typical amplitude 190 • volts peak-to-peak Dornbirn 11th February 2019

11. 1. KORE RADIO FREQUENCY ION FUNNEL DRIFT TUBE-PTR-MS. What it is? Spectrometry for Security Applications– First International Workshop Drift tube acts simultaneously as a conventional drift tube AND an ion funnel The electrode stack with two alternating capacitor networks integrated into the funnel Push-in capacitance strip DC resistor strip Dornbirn 11th February 2019

12. 1. RF ION FUNNEL DRIFT TUBE-PTR-MS. Enhancing selectivity Spectrometry for Security Applications– First International Workshop • The main purpose of the RF field is to focus ions radially by creating repulsive effective potentials at the edges of the electrodes. However, in addition to this intended purpose, the RF results in ions oscillating between electrodes as they drift down the reactor. • Could the high RF fields involved in the operation of the IF be used to enhance collisions of the reagent and product ions with the buffer gas in the DT and hence change either the nature of the initial chemical ionization process or induce CID, respectively, occurring within the DT ? Dornbirn 11th February 2019

13. 1. RF ION FUNNEL DRIFT TUBE-PTR-MS. Enhancing selectivity Spectrometry for Security Applications– First International Workshop IF ON NO IF Product ion intensities as a function of drift tube voltage in RF-mode and DC-mode only. • As the DT voltage decreases (longer reaction time) more collisions in the RFIF region of the DT occur, which enhances CID. • This is due to raising the internal energy of the product ions and the energy of the reactions between reagent ions and neutral species through collisional processes as a result of the applied RF field. Dornbirn 11th February 2019

14. 1. RF ION FUNNEL DRIFT TUBE-PTR-MS. Enhancing selectivity Spectrometry for Security Applications– First International Workshop DFT calculations (using the B3LYP functional and the 6-31+G(d,p) basis set) for the loss of water from TNTH+showed this was energetically favourable, but only when CH3 and NO2 are [1,2] Ortho effect: so, let’s use the DNTs and NTs isomers as probes 3,4-DNT 2,6-DNT 2,4-DNT Similar results for NTs (only 2-NT isomer showed a loss of a water molecule). Percentage product ion distributions for the elimination of H2O from protonated DNT (m/z 165) for the three isomers as a function of drift tube voltage with the IF. Dornbirn 11th February 2019

15. 2. RAPID REDUCED ELECTRIC FIELD (E/N) SWITCHING PTR-TOF-MS Spectrometry for Security Applications– First International Workshop • Thus specificty can be increased by: • 1.- either switching off and on the RFIF at a specific drift tube voltage (still needs hardware development) or • 2.- by switching the drift tube voltage, • We went for option 2 but only in DC-mode, thus changing the reduced electric field (E/N) • The simplest way to provide a rapid change in E/N is to alter the E field by quickly changing the voltage applied across the drift tube • For the switching of the reduced electric field to be analytically usefulfor rapid (< 10 s) thermally desorbed materials, the reduced electric field needs to be changed rapidly (1 Hz or better) Dornbirn 11th February 2019

16. 2. RAPID REDUCED ELECTRIC FIELD (E/N) SWITCHING PTR-TOF-MS Spectrometry for Security Applications– First International Workshop • Enhancing collisional induced dissociation is also achieved by increasing the reduced electric field. • By changing the reduced electric field, changes in product ion distributions (fragmentation patterns) can occur, resulting in a combination of parent ion water clusters, protonated parent and product ions that, in conjunction, can be used to identify an explosive compound with higher specificity. • There is a requirement: KNOW THE DRIFT TUBE VOLTAGES TO SWITCH FROM AND TO (PID plots) Dornbirn 11th February 2019

17. 2. Enhancing PTR-MS selectivity using fast reduced electric field (E/N) switching Spectrometry for Security Applications– First International Workshop Changes in the fractional ion intensities of protonated water and protonated water clusters as E/N is switched between 180 and 80 Td at a frequency of 1 Hz showing (a) raw data and (b) averaged ion intensities. 40 msecacquisition time (25 points per second) There is a time constant of ca. 100 msec due to the reactor’s capacitance Dornbirn 11th February 2019

18. 2. Enhancing PTR-MS selectivity using fast reduced electric field (E/N) switching Spectrometry for Security Applications– First International Workshop Dornbirn 11th February 2019

19. 2. Enhancing PTR-MS selectivity using fast reduced electric field (E/N) switching Spectrometry for Security Applications– First International Workshop RDX, 1,3,5-Trinitro-1,3,5-triazacyclohexane PID for RDX as a function of reduced electric field covering the range 70−210 Td Dornbirn 11th February 2019

20. 2. Enhancing PTR-MS selectivity using fast reduced electric field (E/N) switching Spectrometry for Security Applications– First International Workshop RDX (50 ng) switching between 70 Td and 170 Td at a frequency of 1 Hz Dornbirn 11th February 2019

21. 2. Enhancing PTR-MS selectivity using fast reduced electric field (E/N) switching Spectrometry for Security Applications– First International Workshop RDX (50 ng) switching the reduced electric field at 1 Hz between 70 Td and 170 Td. Dornbirn 11th February 2019

22. 2. Enhancing PTR-MS selectivity using fast reduced electric field (E/N) switching Spectrometry for Security Applications– First International Workshop HMTD, Hexamethylene triperoxide diamine RDX (10 ng) switching the reduced electric field at 2 Hz between 70 Td and 210 Td. Dornbirn 11th February 2019

23. 3. Applications of combining IF and fast E/N switching Spectrometry for Security Applications– First International Workshop Application of combining IF and fast E/N switching at 0.5 kHz between 30 and 180 Td (20 and 190 V across the DT) for TNT (50 ng) Dornbirn 11th February 2019

24. Applications of Direct Injection Soft Chemical Ionisation-Mass Spectrometry for the Detection of Pre-blast Smokeless Powder Organic Additives Conclusions Spectrometry for Security Applications– First International Workshop Dornbirn 11th February 2019

25. Applications of Direct Injection Soft Chemical Ionisation-Mass Spectrometry for the Detection of Pre-blast Smokeless Powder Organic Additives Conclusions Spectrometry for Security Applications– First International Workshop Dornbirn 11th February 2019

26. Applications of Direct Injection Soft Chemical Ionisation-Mass Spectrometry for the Detection of Pre-blast Smokeless Powder Organic Additives Conclusions Spectrometry for Security Applications– First International Workshop 1. Analysis of standard additives. Fragmentation patterns and branching ratios studies in H3O+ and O2+ modes. Table 1. Molecular weight, linear formula and chemical structure for the components investigated PID plot resulting from the reaction of EC with H3O+ reagent ion (80 to 200 Td) as a function of reduced electric field. Dornbirn 11th February 2019

27. Applications of Direct Injection Soft Chemical Ionisation-Mass Spectrometry for the Detection of Pre-blast Smokeless Powder Organic Additives Conclusions Spectrometry for Security Applications– First International Workshop 2. Method validation. Analytical figures of merit Dornbirn 11th February 2019

28. Applications of Direct Injection Soft Chemical Ionisation-Mass Spectrometry for the Detection of Pre-blast Smokeless Powder Organic Additives Conclusions Spectrometry for Security Applications– First International Workshop 3. Application to commercial samples IMR4198 Hodgdon BL-C(2) Mass spectra using water chemistry and reduced electric field of 140 Td showing regions around m/z 170 and 215 and the different composition for both powders. (The insertion represents an expansion of the mass range around m/z 215 (x 20).) Dornbirn 11th February 2019

29. Applications of Direct Injection Soft Chemical Ionisation-Mass Spectrometry for the Detection of Pre-blast Smokeless Powder Organic Additives Conclusions Spectrometry for Security Applications– First International Workshop 3. Application to commercial samples Changes in the fractional ion intensities averaged over each cycle using fast E/N switching experiments at 1 Hz between 90 Td and 180 Td for Alliant Red Dot. The product ions showed are distinctive of 2-NO2-DPA. The dotted line represents the E/N during each phase. Dornbirn 11th February 2019

30. Applications of Direct Injection Soft Chemical Ionisation-Mass Spectrometry for the Detection of Pre-blast Smokeless Powder Organic Additives Conclusions Spectrometry for Security Applications– First International Workshop 3. Application to commercial samples Dornbirn 11th February 2019

31. CONCLUSIONS Spectrometry for Security Applications– First International Workshop • PTR-MS is a suitable technique for fast, sensitive and selective analytical technique for explosives detection • Still has to be tested outside the lab - on the field, i.e. airports, cargo… • Hardware developments have greatly improve PTR-MSanalytical capabilities • All this new developments, although showed for explosives detection, have a clear potential in other research areas (atmospheric, food, etc.) where PTR-MS is present. Besides, they all have helped to develop PTR-MS into a much more versatile and multidimensional analytical technique Dornbirn 11th February 2019

32. Thank you for your attention Spectrometry for Security Applications– First International Workshop. Dornbirn 11th February 2019 Visit my poster! Dr. Ramón González-Méndez MRSC Head Laboratory Technician | Centre for Agroecology, Water and Resilience | Coventry University | E: Ramon.Gonzalez-Mendez@coventry.ac.uk Honorary Research Associate | Molecular Physics Research Group |University of Birmingham  | E: R.GonzalezMendez@bham.ac.uk