Development of a measuring method for germanium and gadolinium

Status:

ongoing 09/2021

Aims:

In recent years, the exposure limits for numerous metals and metal compounds (e.g. indium, germanium) have been lowered or re-established by the competent bodies and committees.

The most recent development in this area is a threshold limit value for gadolinium (Gd), which is currently in the pipeline. This rare-earth metal is used in contrast agents for magnetic resonance imaging, for example. It is suspected of causing symptoms of poisoning in the body. Due to these symptoms, which appear to mirror the symptoms of poisoning, a maximum workplace concentration of 0.85 mg/m³ for germanium (Ge) or germanium oxide (GeO2) in inhalable dust was already established in 2018.

There is currently no recommended measuring method for either gadolinium or germanium. A new measurement method must be developed to measure both metals and their compounds. The method must meet the requirements of TRGS 402. Furthermore, the performance characteristics defined in various standards, for instance the minimum measurement range and measurement uncertainty, must be considered. The aim of the project is to develop a valid, suitable (ICP-MS) measurement method for the metallic elements germanium and gadolinium and to establish this method as a standard measurement method within the MGU.

Activities/Methods:

In the first stage of this project, the individual validation steps for the measurement method were defined, taking into account DIN EN ISO 21832, DIN 32645 and DIN EN 482.

After this, the validation steps for a mass spectrometric method with inductively coupled plasma (ICP-MS) were to be carried out and assessed. Since this is a newly developed process, aspects such as the sampling method or the separation method for Ge/Gd also had to be defined.

Finally, the results were to be analysed and evaluated and the method was to be introduced into the MGU measurement system.

Results:

A method for the quantification of gadolinium from air samples using inductively coupled plasma mass spectrometry was successfully developed and validated in accordance with DIN EN ISO 21832. The validation steps involve the calculation of the limit of detection and limit of quantification (DIN 32645), calibration, analytical precision, reproducibility, repeatability and storage (DIN EN ISO 21832). Since there is currently no defined limit value for Gd, the general dust limit value for the respirable dust fraction (1.25 mg/m³) was used to calculate the minimum measuring range in accordance with DIN EN 482. In addition to the minimum measuring range, a concentration close to the limit of quantification was also validated, meaning that concentrations ranging from 0.01 µg/m³ to 10 µg/m³ can be evaluated. This method for the quantification of Gd using inductively coupled plasma mass spectrometry will be implemented in the MGU measurement system as a standard measurement method. The method meets all of the relevant normative requirements.

The development of a method for the quantification of germanium using inductively coupled plasma mass spectrometry proved problematic. It is not currently possible to isolate Ge in air samples that are to be analysed for Ge using the methods used in the MGU (i.e. aqua regia extraction, microwave-assisted extraction or open extraction using HNO3 and HCl at a ratio of 2:1). Using the traditional methods to isolate germanium results in a recovery between 10 % and 81 %. However, in accordance with DIN EN ISO 21832, a suitable method must demonstrate a recovery of 100 % ± 10 %. During the project, a digestion technique using HF and HNO3 at a ratio of 1:9 was developed. This technique was able to achieve a recovery between 90 % and 95 % with the same substances. The use of HF necessitates a modification to the ICP-MS device, an analytical review of the components involved in the modification and subsequent revalidation of the method.

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