Monitoring of an esterification reaction by on-line direct liquid sampling mass spectrometry and in-line mid infrared spectrometry with an attenuated total reflectance probe

Calibration model transfer in mid-infrared process analysis with in situ attenuated total reflectance immersion probes

Process applications of mid-infrared (MIR) spectrometry may involve replacement of the spectrometer and/or measurement probe, which generally requires a calibration transfer method to maintain the accuracy of analysis. In this study, direct standardisation (DS), piecewise direct standardisation (PDS) and spectral space transformation (SST) were compared for analysis of ternary mixtures of acetone, ethanol and ethyl acetate. Three calibration transfer examples were considered: changing the spectrometer, multiplexing two probes to a spectrometer, and changing the diameter of the attenuated total reflectance (ATR) probe (as might be required when scaling up from lab to process analysis). In each case, DS, PDS and SST improved the accuracy of prediction for the test samples, analysed on a secondary spectrometer-probe combination, using a calibration model developed on the primary system. When the probe diameter was changed, a scaling step was incorporated into SST to compensate for the change in absorbance caused by the difference in ATR crystal size. SST had some advantages over DS and PDS: DS was sensitive to the choice of standardisation samples, and PDS required optimisation of the window size parameter (which also required an extra standardisation sample). SST only required a single parameter to be chosen: the number of principal components, which can be set equal to the number of standardisation samples when a low number of standards (n < 7) are used, which is preferred to minimise the time required to transfer the calibration model.

Reactive carbon fiber ionization-mass spectrometry for characterization of unsaturated hydrocarbons from plant aroma

Carbon fiber ionization (CFI)-mass spectrometry (MS) is an ambient technique that can be used to detect samples in gas, liquid, and solid forms simply by using a piece of carbon fiber as the ionization emitter. Reactive MS can be performed to selectively detect target analytes by conducting fast reactions during ionization. Most ambient ionization MS techniques used to monitor chemical reactions are limited to liquid-phase reactions. Herein, we develop reactive CFI-MS to be a suitable tool for monitoring of reaction products derived from volatile unsaturated hydrocarbons in the gas phase. Hydroamination is a fast reaction that can form a carbon-nitrogen bond through the addition of an amine to unsaturated hydrocarbons. In this study, reactive CFI-MS was used to selectively characterize aroma molecules, which are unsaturated hydrocarbons derived from plants, through hydroamination. A piece of carbon fiber was placed close (~ 1 mm) to the inlet of the mass spectrometer and deposited with dried methylamine. The sample in either liquid or solid form was placed underneath the carbon fiber. The volatiles derived from the sample reacted with amine on the carbon fiber were simultaneously determined once the mass spectrometer was switched on. For proof of concept, ethylene glycol dimethacrylate, which has double bonds and is highly volatile, was initially selected as the model sample to demonstrate the feasibility of using reactive CFI-MS to detect its hydroamination derivative. Banana, garlic, and ginger, which possess aroma molecules with unsaturated hydrocarbons, were selected as real-world samples. Graphical abstract.

Online quantitative mass spectrometry for the rapid adaptive optimisation of automated flow reactors

An automated continuous reactor for the synthesis of organic compounds, which uses online mass spectrometry (MS) for reaction monitoring and product quantification, is presented.