The Development & Evaluation of Hot-stage Microscopy Direct Analysis in Real-Time Mass Spectrometry

The thesis describes the development and evaluation of a novel instrument combining hot-stage microscopy (HSM) with an ambient ionisation technique known as direct analysis in real-time mass spectrometry (DART-MS).

Hot-stage microscopy DART-MS (HDM) combines two complementary analytical techniques to maximise the information obtained from a single experiment. DART-MS has the ability to quickly analyse materials at atmospheric pressure without sample preparation. HSM provides both a controllable temperature stage (essential for accurate thermal analysis) and gives information on the physical changes in a sample arising from a change in colour or morphology.

HDM comprises of a hot-stage designed and constructed to fit between a DART-100 source (IonSense) and an ion trap mass spectrometer (Bruker). It incorporates a digital microscope situated 90° to the DART-MS path and is focused on samples placed in metal or ceramic crucibles on the hot-stage. Experiments typically use samples of a few milligrams in mass and heating rates of 0.1 to 50 °C min-1 standard for many conventional thermal analysis techniques. Software was developed using Visual Studio 2017, (Microsoft) to control the hot-stage, collect micrographs and record optical and colorimetric data in real-time. Software was also developed to extract selected ion intensity data from the MS and combine it with temperature and optical data.

HDM was successfully evaluated with a range of applications. Synthetic organic reactions have been performed in situ. Reactants, products and transient intermediates were successfully monitored and profiled as a function of temperature, with correlations between the reaction colour and micrographs being made to mass spectra. Physical properties of common polymers including melting points, cold crystallisations and glass transitions have all been shown optically with relation to their mass spectrum. An optical method to measure and calculate the coefficient of thermal expansion (applied to silicone polymers) is described and shown to be consistent with literature data. HDM has also been applied to the thermal profiling of inks adsorbed on alumina matrices. Studies with mixtures of energetic materials collected from surfaces demonstrate that limits of detection at the nanogram level are readily achievable.