Application of laser induced breakdown spectroscopy in food container glass discrimination

Abstract

Although glass is primarily silicon dioxide, manufacturers produce different types of glass by blending various other oxides to impart desired functional properties. In this study, the application of laser induced breakdown spectroscopy (LIBS) as a rapid tool for glass discrimination was examined, focusing on glass used for food packaging applications (soda-lime-silicate glass). The LIBS instrument operational parameters and applicable calibration methods were evaluated using National Institute of Standards and Technology certified glass standards. LIBS-based spectra of emission lines for selected elements were recorded on a pool of mixed glass samples taken from assorted food containers and other non-food packaging glass including labware, electronic display glass and glass used for different types of lighting. Owing to a greater contrast in composition, an excellent discrimination between food container glass and the other types of glass was demonstrated by post-processing the emission line data with a correlation matrix, multivariate data visualization and clustering techniques. Some significant within-glass category difference were also detected when a set of glass jar samples taken from different food brands were evaluated using clustering analysis. The latter shows a sensitivity to distinguish smaller differences among the soda-lime-glass that could be attributed to a manufacturing variation. The significance and stability of the group association patterns, generated by the clustering analysis, were further confirmed with uncertainty analysis using the method of bootstrap re-sampling and bootstrap probability calculations. Results of the study suggest that LIBS measurement coupled with appropriate multivariate calibration, data visualization and clustering analysis can be utilized as a rapid tool for glass identification and to support food safety investigations by helping to trace the identity and source of glass fragment inclusions.