Characterizing the Unknown

Posted on August 17, 2023

We often encounter very open-ended research questions. Clients regularly ask us to perform chemical characterizations of ill-defined materials, namely to support the remediation of fouling problems in industrial systems. To figure out the chemical make-up of an unknown substance, we offer certain key steps:

For liquid, solid, and semi-solid samples, the first step is to try and break down the material composition into 3 main bins:

  • Inorganic solids
  • Water and dissolved aqueous species
  • Organic material

The isolation of inorganic solids can be accomplished by reflux-boiling solvent extractions (such as Dean-Stark), which allows for the removal of organic matter and water. The bulk of the compositional information on the inorganic fraction can then be obtained by Inductively Coupled Plasma / Mass Spectrometry (ICP-MS) which gives an elemental breakdown of the inorganic components and X-Ray Diffraction (XRD) which provides crystallographic data.

One of the most robust techniques for evaluating the water content in a sample is Karl Fischer titration, namely because of its selectivity. This method is based on the oxidation of a sulfite into its corresponding sulfate with iodine, which requires the consumption of water. The analyzer measures the quantity of iodine consumed through the titration and relates it to the water content in the sample based on the reaction stoichiometry.

The analysis of dissolved aqueous species requires the isolation of the water phase (gravity separation, filtration, centrifuging). The dissolved species can then be identified by different methods, such as ICP-MS, IC, LC-MS, or solvent extraction followed by GC (for dissolved organic compounds).

Lastly, the organic material in the sample can be characterized after extracting the sample with a hydrophobic or amphiphilic solvent, and analyzing the extract by GC-MS.

This suite of analyses offers significant insight in the chemical composition of a given material. However, some other techniques could be better suited to a targeted compound of interest, and analytical plans should be adjusted accordingly.

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