Measuring Sb in plastics with LIBS

In this study, the feasibility of measuring the Sb content in different plastic materials by laser induced plasma spectroscopy (LIBS) is explored. Measurements were performed initially on a sample of pure Sb in order to identify the most prominent element transitions before different consumer plastics of varying matrix, composition and color were examined. The experimental set-up was based on a single pulse laser excitation at 1064 nm and a detection system consisting of an array of three compact spectrometers covering the range 236–796 nm. On pure Sb material, many atomic lines, particularly intense in the UV region, were observed, together with much weaker ionic transitions mainly in the visible spectral region. Unfortunately, all of the strong Sb transitions partially overlapped with those from Si, Fe and Ti, elements common in many plastic materials. For constructing the calibration curve for Sb content we exploited the Sb concentration values obtained by X-ray fluorescence (XRF) spectrometry, which varied from the detection limit (∼200 ppm) up to 65 000 ppm. The analytical Sb I line at 276.99 nm was selected because, even if it has a weak contribution from one Fe I transition, its empirical subtraction leads to a well-correlated linear calibration graph. The corresponding detection limit was around 1400 ppm while in the absence of Fe, having an intense ionic transition at 259.93 nm, it is possible to use a more intense Sb I transition at 259.81 nm, achieving sensitivity on the order of 100 ppm.