Development of a measurement method for organotin compounds

Status:

completed 04/2024

Aims:

Owing to their known human and ecotoxicity, organotin compounds (OCTs) in consumer products and in the environment are subject to extensive regulation (REACH Regulation No 1907/2006). However, their excellent physical and chemical properties continue to make OCTs among the most important technical organometallic compounds. Notable areas of application include the plastics production and processing industry, where they are used as process catalysts and stabilizers; surface hardening in glass production; electroplating; electrical engineering; and in the synthesis of numerous industrial and speciality chemicals. In these industries, the compounds may be released at workplaces in the form of vapours or dust particles, and absorbed both by inhalation and through skin contact. Occupational exposure therefore presents a potential risk to workers. TRGS 900 defines occupational exposure limits (OELs) for a total of 23 OCTs. These limits differ in their concentrations, and relate to the content of the tin element. Specific measurement methods that make distinction between these assessment criteria and monitor them do not yet exist. A feasibility study was conducted in a master’s thesis in which a liquid chromatography method employing high-performance liquid chromatography coupled to inductively coupled plasma (HPLC-ICP-MS) was developed for separation of 11 OCTs subject to regulation.

The aim of the present project is now to develop a specific measurement method suitable for the OCTs monomethyltin (MMT), monobutyltin (MBT), monooctyltin (MOT), monophenyltin (MPhT), dimethyltin (DMT), dibutyltin (DBT), diphenyltin (DPhT), trimethyltin (TMT), tributyltin (TBT), triphenyltin (TPhT) and tetramethyltin (TTMT), and to establish it as a standard measurement method in the MGU measurement system.

Activities/Methods:

The project is based on a master’s thesis in which the separation method was to be developed. In the first phase of the project, the HPLC-ICP-MS separation method was optimized with respect to data analysis, laboratory procedures and suitability for use in contract analysis. The second phase concerned development of a suitable sampling method for OCTs. In the third phase, tests were conducted to develop a species-preserving sample preparation process. A separation method with structure elucidation for determining the OCTs by means of HPLC-MS was developed in the form of a feasibility study. The primary purpose of this method was to identify the OCTs and distinguish them from any interference compounds occurring in real-case workplaces. Finally, all steps of the analytical process (sampling, sample preparation, analysis) had to be adjusted to each other.

Results:

During the project, the analytical method employing HPLC-ICP-MS for determining 11 organotin compounds in workplace air was optimized and developed further. The method was extended to include the analytical steps of sampling and sample preparation.

Performance of the resulting HPLC-ICP-MS-based method was optimized with regard to laboratory procedures and handling of the unstable analyte standards. Data analysis was also made more efficient. Comparative studies of the new HPLC-ICP-MS method and the ICP-MS-based analysis principle used previously were performed on real-case workplace samples, and used successfully to identify organotin compounds present.

To enable the compounds to be quantified reliably, sampling and sample preparation had to be selected and optimized such as to ensure that the compounds were retained throughout the analytical process. The different physical and chemical properties of the 11 organotin compounds, in particular their reactivity and instability, presented a particular challenge in this respect. Following performance of extensive suitability tests, the GGP-Mini was selected as the sampling system, with a combination of glass fibre filter and activated charcoal tube as the sample holders. The commercial availability of the sample holders facilitates their preparation and handling during contract analysis. Sample preparation was optimized for recovery of the 11 compounds by performance of systematic comparative tests employing different extraction mixtures. A feasibility study was also conducted into the use of HPLC-MS/MS for structure elucidation of the complexes formed and any interfering compounds. The workflows of the method developed for sampling, sample preparation and analysis were adapted to each other efficiently for application in contract analysis. The results of the project have been published nationally and internationally in several scientific papers (including presentations and posters). Among these are an article in Journal of Chromatography A, a prestigious international journal in the field of analytical chemistry (impact factor: 4.1).

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