title: Development of a standard addition method for quantitative LA-ICP-MS analysis
Creators: name: Bielecki, Konrad
Publisher: name: TU Wien
Year: 2023
Subjects: subject: LA-ICP-MS
subject: calibration material
subject: polymer

description: Liquid Inductively coupled plasma mass spectrometry (ICP-MS) offers an established method for the quantification of trace elements in various samples. However, the need to digest solid samples first risks contamination and creates a high workload. This approach also only offers bulk information. Circumventing this with LA-ICP-MS measurements is preferable but it also has its problems. The difficulty hereby lies in the quantification process. Certified reference materials are expensive, not available for novel materials, and often do not match the matrix of the sample material precisely. This creates a massive problem when researching new materials of unknown composition and forces one to develop workaround in house methods like the dry droplet technique, microwells or preparation of powdered pellets or tablets. However, those are often hamstrung by issues of inhomogeneity and replicability.This research is dedicated to developing a new standard addition method to circumvent those problems and make it applicable to polymer films. An HTX TM-Sprayer was used to evenly deposit liquid standards onto the surface of polymer films. This process was optimized with a series of experiments varying the composition of the solvent by changing the concentration of Polyethylene glycol, Isopropanol, and water, to achieve a homogeneous distribution of residues after solvent evaporation. Variation of dissolved analyte allows preparation of standards with known contents, which were then measured with LA-ICP-MS, resulting in a calibration function. Measurements of identical standards show a standard deviation of 0.68 %. The standards can further be created and stored for multiple months without any changes to their quality, indicating very good stability at 20 to 25 °C.Liquid ICP-MS measurements of those sprayed and microwave digested standards were performed to determine the relation of the elemental concentrations in the applied liquid standards to the respective amounts in the applied coating, which resulted in a factor dependent on the thickness and density of the investigated material. This factor was then used to modify the previously obtained calibration curve. The developed method was then applied to determine the concentration of native Sulfur in a commercially acquired Kapton film.The results were evaluated with a reference measurement since there were no Certified Reference Materials available at the time of this work. Microwave assisted acid digestions of unsprayed Kapton were performed and the solutions were analyzed with liquid ICP-MS. The results derived with both methods are in good accordance.Additional polymer films, namely Nafion® and Polystyrene film, were also investigated and evaluated. The obtained results show good properties in terms of linearity, applicability, and reproducibility on other polymers. This new standard addition method further shows great potential for flexible calibration of a wide array of elements such as S, Pb, Zn, Sn, Ag, etc. Additional experiments also show promising results for other substrates like Cu, Si, or Al.However, it was not possible to successfully execute reference measurements for all samples due to stability issues of certain polymers such as Nafion® and the inability to perform liquid ICP-MS.