Polydimethylsiloxanes (PDMS) are worldwide the most often used silicon-based polymers, because of their outstanding properties. Routinely used ICP methods revealed the ability to quantify ultra-trace levels of PDMS as silicon in volatile and non-volatile organic solvents. But the drawback of ICP is that it is only suitable for the determination of total silicon; distinguishing between different silicon components is not possible.
A combination of size exclusion chromatography (SEC) and Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) closes this gap and enables highly flexible separation of organosilicon compounds by molecular weight [1] but fails to achieve the necessary quantification limits of PDMS. Therefore, triple quadrupole (QQQ)-ICP-MS was selected as detection system, because of its known higher sensitivity and larger linear range. Challenges, such as plasma stability, destruction/damage of the materials and hardware used, had to be overcome during method development.
This presentation provides a detailed overview of the various development steps of this novel application for the separation, characterization and quantification of organosilicon compounds and highlights the opportunities and limitations it offers. The newly developed method enables the determination of silicon distribution versus molecular weight at sub-ppb levels. The response is uniform over a wide range of molecular masses (186000 to 311 Da) under the used conditions which provides a universal calibration, allowing the quantification of a huge variety of organic silicon-components. Application examples highlight its suitability to solve different existing industrial challenges.
ICP-MS combined with size exclusion chromatography (SEC) can open new possibilities for applications in fields far beyond the Si-organic-compound speciation and quantification, where information on the chemical composition of (complex) element-organic-polymers is desired. The work presented here will hopefully stimulate more intensive use of ICP-MS as an additional detector in the field of separation to open up a further dimension to polymer characterization research.
Literature:
[1] Vogel, K.; Wegener, A; Pursch, M.; Luschas, P. and Wiesmann, M.; SEC–ICP-OES Hyphenation: Speciation and Quantification of Polydimethylsiloxanes at Trace Levels; Spectroscopy 34(1): 38 – 46, January 2019
