A Guide to the Characterisation of Unknowns

Wed 05/27/2026 - 17:07

Unknown materials can be any substance that is somewhere it shouldn’t be through an unknown source. This can include dust, liquid, precipitates, solids, soil and grease, waste, or pharmaceutical samples.

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The experts at SOCOTEC can characterise unknown substances through a specialised testing process using an extensive library of data.

The process to characterise unknowns starts with a client consultation – investigating the history and background of the issue and attending the site in question when the investigation requires. There is then the analysis of the unknown using several state-of-the-art instrumental techniques.

The testing process begins with a visual examination, before analysis takes place using the relevant instruments, tailoring the techniques to the sample.

FTIR (Fourier Transform Infrared Spectroscopy) – collects high-resolution spectral data with an infrared spectrum of absorption or emission of a solid, liquid, or gas.
SEM-EDX (Scanning Electron Microscope and Energy-Dispersive X-Ray Spectroscopy) – provides high-resolution imaging and elemental composition analysis of materials in the sample.
GC (Gas Chromatography) – separates compounds in the sample based on their mass to charge ratio to inform the organic content.
ICP (Inductively Coupled Plasma Mass Spectrometry) – detects and quantifies trace inorganic elements and metals in the sample.

The data collected is then compared to SOCOTEC’s extensive library which consists of three decades of unknown substance data, with expert interpretation identifying the unknown substance.

A Guide to the Characterisation of Unknowns

One such example gathered was that of a diesel multiple unit passenger train experiencing premature blocking of its filters from an unknown substance and airborne materials such as feathers, leaves, seeds, and cellulose. This was reducing the flow through the turbo and causing loss of power to the engine.

SOCOTEC tackled this by doing a visual examination of the filter and removing the substance from the filter for testing. A SEM examination was completed, detecting iron and plant material. Further tests were carried out to match the metallic material found to the wheels, coming from general wear and tear of the wheels while in use, while additional analysis matched silicon material to the ballast dust from the tracks.

It was clear that this build-up of substances in the filters was a result of airborne material and the external environment that the train was travelling through. In order to prevent the continuation of build-up in the filters, SOCOTEC was able to help improve and reconstruct the filters. As a result of SOCOTEC identifying the source and size of the material, housing and pre-filter cases were developed and placed around the filter, and the size of the filter was adjusted to prevent future blockage.

Another example demonstrates the diversity of work that can be undertaken when it comes to unknown materials. Cars in a car park were starting to get covered in a yellow and brown substance, appearing quickly and suddenly.

SOCOTEC attended the site, took swabs of the unknown substance on the cars and analysed it, quickly discovering it was insect-based. SOCOTEC has been collecting data from substances for over 30 years, building up a library of relevant substances. By analysing the unknown substance on the cars and comparing it to SOCOTEC’s data library, the substance proved to have a similar fingerprint to previously examined butterfly waste.

After informing the company, it was found that new plants had been planted within the car park that had attracted a new type of butterfly, causing the sudden appearance of the yellow-brown substance from the butterflies to show on the cars.

In a similar scenario, a black deposit had begun to build up on cars in another car park.

SOCOTEC analysed a sample by FTIR, GC-MS, and SEM methods to identify a rubber-like substance. The confusion came in that the substance’s composition had been altered, with the rubber not matching the tyre production facilities present on-site.

The site was attended to investigate after the testing analysis, which led to the identification of a chimney, close to, but outside of the site. The company which owned the chimney was contacted and the substance inside the chimney analysed, revealing that they had recently stopped their preventative cleaning schedule of the chimneys. The build-up inside the chimneys therefore caused the precipitate coming down and on to the cars parked nearby. This was rectified by the company re-implementing their preventative cleaning schedule to the chimneys.

Unknown materials can be a major cause for concern, and SOCOTEC’s Advanced Chemistry and Research team can provide tailored testing services to a broad range of industries, helping to identify unknown substances found on-site, in products, or during processing, as well as providing individually designed solutions.

For more information regarding SOCOTEC’s services and identification of unknown substances, please contact us.