Development of a measuring method for chromium (VI) compounds using ion chromatography

Status:

completed 02/2022

Aims:

With a few exceptions such as barium chromate, chromium(VI) compounds have been classified as carcinogenic (1b), skin sensitising and sometimes respiratory sensitising. Chromium(VI) compounds are used in numerous industries. They are used in manufacturing processes, such as galvanic chrome plating of surfaces, chrome tanning of leather and as an oxidising agent in chemical processes. Furthermore, chromium(VI) compounds can occur unintentionally, for instance in the process of welding chrome alloys or burning cement. An exposure–risk relationship (ERR) for chromium(VI) compounds could not be derived. The risk-related assessment standard (AS) of 1 µg/m³ (calculated as Cr) applies for the inhalable fraction. If the exposure remains below the AS concentration, there is a non-quantifiable, low risk of lung cancer. For the measurement process, this means that a concentration of 0.1 µg/m³ must be reached as the lower workplace exposure limit in accordance with DIN EN ISO 20581. There is currently no suitable method capable of fulfilling this requirement. The photometry method currently used in the hazard identification measurement system of the accident insurance providers (MGU) (DGUV Information 213-505) is susceptible to interfering substances such as iron(III), vanadium(V), mercury(I, II), molybdenum(VI) and nitrates and cannot be optimised further.

The aim of this project is to develop a robust, sensitive measurement method for chromium(VI) compounds which can achieve a detection limit under 0.1 µg/m³ and is based on an ion chromatography (IC) analysis method.

Activities/Methods:

After setting up the ion chromatograph, different filter materials are first tested to gauge their suitability. If the blank values and recovery rates are satisfactory, the method to be developed will be validated in accordance with DIN EN ISO 20581 and ISO 21832. This will include testing of the following points: storage stability, detection limit, recovery rate, blank value, interferences, humidity/temperature influences.

First, a method for air samples will be developed. Only when this has been successfully validated, eventually material samples will be included. Due to the chromatographic separation of the sample through IC, matrix influences are largely ruled out, and the accumulation of chromium(VI) leads to significantly higher sensitivity.

The method is to be extensively tested in the scope of practical measurements and be established as a standard method in the MGU.

Results:

A method has been developed for the detection of chromium(VI) in workplaces. The focus was on the selection of suitable filter material. Filter types from different manufacturers were tested with regard to their properties during sampling and their blank values. The PTFE membrane filter TE 38 from Whatma^TM with a pore size of 5.0 μm met the requirements. This filter is free from blank values irrespective of batch and allows four-hour sampling with an airflow rate of 10 l/min.

The validation of the method showed a detection limit of 0.0007 µg/m³, an average recovery rate of 96.6% and a stable storage period of 6 days. The requirement for the working range of the method to detect a value of 0.1 µg/m³ was achieved. The validated working range is between 0.042 µg/m³ and 0.42 µg/m³. For samples with higher concentrations, the analysis solutions can simply be diluted, meaning the method meets all criteria required of it as a measurement method.

After successful validation in the laboratory, test series were undertaken in three companies in the galvanic industry in order to compare the current photometric measurement method with the new ion chromatographic method in a practical test. The results of both methods were reproducible and able to be compared successfully. The storage stability of the samples from the galvanic companies confirmed the results obtained in the laboratory. Samples for chromium(VI) must be processed and analysed within six days.

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