Mass Spectrometry
intermediates and products in real time. In some applications the off-gas is measured with special microflow capillaries to minimise depletion. The response to gas composition changes measured through the nano-porous membrane is typically less than 0.5 second.
Fast response of the mass spectrometer is crucial when following dynamic experiments such as DEMS (differential electrochemistry mass spectrometry). Here an electrochemical cell is coupled to a real-time mass spectrometer via a porous membrane. The experiment is performed by scanning the electrode potential while analysing the gas evolution using the mass spectrometer. The data below shows the H2 evolution during a DEMS experiment.
For thermo-gravimetric mass spectrometry, TG-MS
Using special adaptors, Real time mass spectrometry can be confi gured for continuous analysis of evolved gases and vapours from
thermogravimetric analysers, TGA.
Figure 10: Benzene in water analysed by MIMS at low concentration. and can operate from solar powered rechargeable battery packs.
An example of the advantages of real time gas analysis is in water contamination studies. The example below shows the analysis of dissolved benzene in water. Without real time analysis water samples would need to be taken to a laboratory for analysis.
For electrochemistry studies
Real time mass spectrometry in electrochemistry uses a special interface designed that includes a Nano-porous membrane interface for fast response in- situ determination of gaseous and volatile electrochemical reactants, reaction
This coupling is known as TGA-MS. Each TGA model requires its own connection type interface. The TGA interface includes re-entrant furnace sampling, providing close coupling to the TGA furnace region for optimised evolved gas/ vapour analysis.
The coupling interface includes bespoke cables connecting the TGA
Figure 13: TGA interface with mounting clamp and re -entrant alumina furnace probe.
and MS for TGA-MS synchronised data acquisition including automatic start / stop with TGA operation. Without real-time mass spectrometry the data available from a TGA does not provide any information about the identity of the evolving gas.
Figure 14: Real-time gas analysis study of the kinetics of the methane oxidation reaction. For Catalysis Studies
Figure 11: A typical DEMS cell that couples to real time mass spectrometer via the KF-25 support fl ange shown.
Real time mass spectrometry offers solutions for experimental catalysis research, from initial catalyst characterisation and reaction testing to downstream optimisation of catalytic activity. The ability to follow multiple species in real time over a high dynamic range makes the real time mass spectrometer ideal for catalysis studies including temperature programmed reaction, oxidation and reduction studies.
The use of real time mass spectrometry can be crucial for studying the kinetics of catalytic reactions where delays in analysis would affect the results considerably. The data below shows the fast kinetically useful data available with real time mass spectrometry.
Conclusion
We have illustrated how the components of a quadrupole mass spectrometer; the ioniser, mass filter, and detector assembled as a flange mounted analyser gauge head, configured with UHV system and special sample inlet become a powerful real time analyser with fast response, and high dynamic range for detecting multiple species.
Figure 12: Data from a DEMS experiment.
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