In-situ analysis: direct measurement of the sample in its ‘original position and state’

‘In situ’ is a term that is frequently mentioned but often glossed over. Its precise meaning is: conducting analysis directly at the sample’s original location or in its original state, without removing, transferring or disturbing its original environment. The opposite of this is ‘off-site/offline’—where the sample is first collected, preserved and pre-treated, before being taken elsewhere for analysis. The distinction may appear to be merely a matter of ‘where the measurement is taken’, but in reality it determines whether certain information can be detected.

Why are location and state so crucial? Because many analytical targets ‘change the moment they are disturbed’. Reactive intermediates and short-lived free radicals in a reaction system often react and disappear before they even reach the detector, once they have undergone sampling, cooling and chromatographic separation; the spatial distribution of molecules in biological tissue is lost forever once the sample is homogenised or moved. The value of in situ analysis lies precisely in preserving this volatile information ‘on the spot, in real time and with minimal disturbance’.

In situ analysis is embodied in two ways across Neo Source INSTRUMENT’s two product lines. The first is ‘in-situ reaction’: the ProC-1C in-situ catalytic/pyrolysis mass spectrometry analysis system can perform in-situ online diagnostics on the pyrolysis and gasification products (including free radicals) of coal, biomass and solid waste, as well as characterise gas-phase and solid-phase catalytic products—there is no need to wait for the reaction to finish or to channel the gas to a remote location; sampling and ionisation take place whilst the reaction is still occurring. For details on the detection of reactive intermediates such as free radicals, please refer to the dedicated article ‘Free Radicals and Reactive Intermediate Species’; for the differences between online and offline sampling methods, please refer to ‘Online Analysis and Offline Analysis’.

The second aspect is ‘spatial in situ’: mass spectrometry imaging is, in itself, a form of in situ, non-destructive sampling—data is collected point by point directly on tissue sections without altering the spatial position of the sample; after imaging, the sections remain intact and can still undergo H&E histopathological examination. MSI DPI (20–200 μm) and MSI LDPI (2–3 μm) apply the concept of ‘in situ’ to the spatial dimension, enabling the molecular distribution to be recorded in situ. Both sources can be fitted to mass spectrometers from Agilent, AB SCIEX and Thermo; the ProC series of online mass spectrometers offers a mass resolution of 3500 and a sensitivity of 10 ppb.