What Is That?? Identifying Unknown Particles

One of the most difficult problems dietary supplement and food manufacturers face is identifying unknown materials or substances discovered in their products as a result of routine quality assurance (QA) testing or consumer complaints. Determining what these materials are and how they ended up in the product can become a major concern. This is where a commercial laboratory that specializes in identification of unknowns can help.

These investigations start with a collection of background information as to how and when the problem was discovered. Then, a visual inspection of the unknown material is performed to better understand morphology and homogeneity of the unknown substance. If the unknown substance is distinct and does not appear to be biological in nature, micro analytical techniques such as Fourier Transform Infrared (FTIR) Spectroscopy for organic samples or Scanning Electron Microscopy (SEM) with Energy Dispersive Spectroscopy (EDS) for inorganic samples are chosen. Biological samples are processed using microbiological plating methods, biochemical methods and/or Polymerase Chain Reaction (PCR).

Sometimes the unknown substance needs to be separated from the material in which it was discovered. In these cases, separation techniques such as Gas Chromatography (GC) for volatile compounds, High Performance Liquid Chromatography (HPLC) for nonvolatile compounds or Gel Permeation Chromatography (GPC) for compounds of varying molecular weights are utilized. A flow chart of the identification process utilizing the most common analytical techniques is shown in Figure 1.

Three examples of typical industry problems and how a laboratory goes about the process of identifying the unknown substance are outlined below.

An organic foreign object identified during routine quality assurance: A food processor discovered a foreign object within its product during routine quality assurance testing. The foreign object appeared to be polymeric based upon visual inspection using an optical stereo microscope, and a test specimen was obtained for analysis by FTIR spectroscopy. FTIR works by exciting chemical bonds with infrared light. Chemical bonds in this excited state absorb light energy at frequencies unique to the various bonds. This activity is represented as a spectrum, a “chemical fingerprint” of the compound. The unknown spectrum is then searched against libraries of reference spectra to identify the material.

FTIR testing identified the material as PolyVinyl Chloride (PVC), a polymer typically used in food contact equipment and hand tools. At the client’s request, a similar test specimen was obtained from a hand tool (a large spatula) used in the manufacturing process. FTIR testing of this known sample gave an identical spectral fingerprint, indicating this as the most likely source of the foreign object.

An inorganic foreign object identified during routine QA: A food manufacturer identified reddish particles on the top surface of its product after processing. The particles were suspected to be metallic after visual inspection using an optical microscope. A test specimen was removed for analysis by SEM with EDS since the sample was suspected to be inorganic. The scanning electron microscope is a large vacuum tube inside which the sample is inserted. Electrons are generated in the vacuum tube from a heated filament and driven by a high voltage to the sample, which is conductive or which has been made conductive by coating with a conductive material. The SEM generates an image of the sample from this electron beam. In conjunction with generating images, the electrons generate X-rays from the surface of the materials in the sample. The X-rays emitted from the sample can be interpreted using EDS to determine of which elements (atoms) the surface of the sample is composed.

The elemental composition of the unknown particles was determined to be iron-bearing metal flakes. The elemental composition was consistent with the composition of suspect particles from overhead duct work.

An organic foreign object identified as a result of a consumer complaint: A food processor received a complaint that consumers experienced an un-natural hot sensation after ingesting its product.

Upon visual inspection of the product, no distinct contaminants were identified. A liquid extraction was performed on the product, and the sample was analyzed by HPLC, a technique that separates compounds dissolved in solution.

The solution is passed through a stationary phase known as a column. The compounds are separated based on polar chemical attractions of some compounds to the column. The compounds attracted to the column slow down causing the sample to pass through the column at different rates, separating the constituents.

HPLC testing identified the presence of capsaicinoids in the food product. Capsaicinoids are the active ingredients found in various pepper varieties and are the cause of the hot sensation experienced upon eating a pepper. 

Hollie Rasmussen is the business development manager with Microbac Laboratories Inc. in Boulder, Colo. Microbac is a full service chemical, microbiological and physical testing laboratory, with extensive expertise in and analytical capabilities for identification of unknown materials. For more information, visit www.microbac.com, call (303) 579-0855, or e-mail [email protected].