Metal analysis in polymers using tandem LA-ICP-MS/LIBS: eliminating matrix effects using multivariate calibration†
Nowadays, metal analysis in polymers is experiencing growing interest due to increased environmental regulations and the need for sustainable polymer recycling strategies. Quick and reliable analyses are required to fulfill the demands of today's industry. Due to the high chemical inertness of most polymers, traditional solution-based analysis is often not an option and solid-sampling techniques such as Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) or Laser Induced Breakdown Spectroscopy (LIBS) have to be employed as an alternative. These, however, are typically prone to matrix effects and for each polymer type a separate reference material with known concentration may be required – an approach which is obviously not suitable if the polymer type is not even known. To overcome these difficulties, a tandem LA-ICP-MS/LIBS procedure coupled with statistical analysis has been used in this study. LIBS is known to be especially prone to matrix effects – which has been used as a benefit here. Complete broadband LIBS spectra with a wealth of information have been used as signatures for the investigated polymer types (polyimide, polymethylmethacrylate and polyvinylpyrrolidone) to serve the purpose of reducing matrix effects. While LIBS allowed the detection of alkali metals and alkali earth metals even at lower concentrations, LA-ICP-MS was used simultaneously for the analysis of other trace metals in the μg g−1 regime. Na, Sr, Co, In, and Pt were used as exemplary analytes at concentrations ranging from as low as 0.1 μg g−1 up to 300 μg g−1. Using the combined dataset of all three polymer types (in total 23 samples), multivariate calibration models could be constructed for all elements of interest. Validation was performed using a set of 22 external samples showing relative average deviations from their actual elemental content of 4.4%, but not more than 9.6%.