Christoph Grimmer

Characterization of petrochemical compounds using thermal analysis hyphenated to photoionization mass spectrometry

Due to a decline of high quality crudes but consisting demand for fuels, energy and building blocks, a shift towards heavier resources can be recognized. Heavy crudes (or their products) are challenging even for state of the art analytical techniques, because of their low volatility, low solubility and increased complexity. These characteristics impede separation by chromatography and mass spectrometry. Usually, these problems are faced by high-end methods such as direct infusion HR-MS or by utilization of many complementary techniques.

Our approach revolves mainly around a coupling between a thermal analyzer and soft photoionization mass spectrometry. This way we are not limited by column temperatures or solvents. The sample can be heated to 1000°C or more by a defined temperature program. The organic part evaporates or decomposes and the evolving compounds are transferred via a heated capillary into the ion source of a TOF. Here, either universal SPI or selective REMPI is applied. Photons from single photon ionization have an energy of 10.5 eV and ionize all substances with an ionization energy below that. For resonance enhanced multi photon ionization photons with a wavelength of 266 nm are used. At least two photons are needed to reach the ionization continuum, thus only molecules with a relatively stable excited state can be ionized, which is the case for most aromatics. Due to the soft and selective ionization, complex spectra can often be well resolved even when low resolution mass analyzers are used. Mass traces can be tracked time resolved with a frequency of 10 Hz.