10 Years Automated Particle Identification by Combining Image Guided Raman and Laser Induced Breakdown Spectroscopy (LIBS)

Lisa Krapf, rap.ID GmbH, Berlin, Germany
Oliver K. Valet, rap.ID GmbH, Berlin, Germany

Purpose: Particulate contamination is a major issue in different areas like environment, pharmaceuticals, food and beverage or technical cleanliness. Apart from determining the number of particles in a sample, it is of major interest to identify the material to be able to eliminate particle sources or assess the risk caused by particles in the product. For determination of the material different spectroscopic methods are available. Raman spectroscopy allows the identification of organic substances like polymers, cellulose or proteins. However, some materials like metals are not Raman active and thus cannot be identified. On the other hand, LIBS allows elemental analysis of a material and can identify the composition of metals and inorganic materials. Since 10 years the Single Particle Explorer offers the only instrument with Raman and LIBS to identify organic as well as inorganic and metallic particles. Over 150 instruments are industrially used mainly in the pharmaceutical industry. We show several case studies and discuss one full automated measurement in detail:

Methods: Particles were collected on a gold coated polycarbonate filter. To avoid movement of particles caused by pressure waves due to plasma formation in LIBS, particles were fixed on the filter using polyurethane glue. An area with 18 mm in diameter was scanned in dark field with a 20x objective and all particles larger than 2 μm were counted. Automatic Raman and LIB spectroscopy were performed to analyze the 20 largest particles on the filter.

Results and Conclusion: Figure 1 shows the results of an automated analysis of the 20 largest particles on the gold coated filter. Several materials including Polvinyl chloride, Steel, Diamond and silicon carbide were identified. From the result table it can be seen that all 20 largest particles are identified with a combination of Raman and LIB spectroscopy. A combination of both methods therefore allows a significantly higher determination rate and makes it possible to identify sources of contamination of any kind in a sample.

Figure 1: Results of particle counting and material identification. An area of 18 mm in diameter scanned with a 20x objective in dark field mode is shown on the left hand side. Particles are white spots on a black background. The table on the right hand side shows the size of the 20 largest particles and the results of Raman as well as LIB spectroscopy on every single particle.