Minute amounts of organic contaminants can be extremely difficult to characterize. Some of the highest resolution microanalytical methods, such as field emission SEM and TEM, provide detailed morphological and elemental information about samples; however, this information may be of little use when the particle of interest is organic and composed largely (or entirely) of carbon, hydrogen, and oxygen.
While no single method is applicable to every sample, particularly when working with mixtures or a complex sample matrix, a suite of microchemical methods, combined with precise sample preparation and experienced interpretation, can provide a wealth of information from unknown organic particles less than 10 micrometers in size. Such particles might be a protein, carbohydrate, or something else, such as a rubber, dye, pigment, or active pharmaceutical ingredient.
At Microtrace, we utilize a combination of chemical and optical properties to characterize, constrain, and identify microscopic particles both organic and inorganic. For example, chemical information was collected from a 7 micrometer particle by means of infrared microspectroscopy.
Other methods such as polarized light microscopy, Raman microspectroscopy, and classical microchemical tests are used in conjunction with microspectroscopy to provide specific chemical information for micrometer sized particles.
Case examples include: the identification of pigmented particles, such as the red flake above; sourcing chars to their source material; and the identification of unknown microscopic particles.
In the case of carbohydrates, it is often possible to identify a carbohydrate more specifically (e.g., sucrose, microcrystalline cellulose, paper fiber, hardwood, softwood, or another type of natural fiber, to name a few). While such distinctions may seem obvious for macroscopic samples, such distinctions can be more challenging for microscopic particles, and often multiple optical and chemical microanalytical approaches are required to identify and source microscopic particles of organic compounds.
Related standardized methods: ASTM E2403