Identification of method metrics for VOC measurements by means of the test gas stream

Status:

completed 10/2009

Aims:

The number of measurements of volatile organic compounds (VOCs) conducted in indoor areas for risk assessments in the context of the accident insurance institutions' (BGMG) hazardous substances measurement system and for the testing of emissions from printers and photocopiers has risen continually over the years. The number of individual components to be considered has also risen to over 40, owing to the publication of new recommended values by the German Federal Environmental Agency (UBA) and to changes in the test principles for printers. For the method for VOC measurement, collection on Tenax TA tubes followed by thermal desorption and gas chromatographic analysis, the method metrics have not been available up to now for all individual components. For full validation of the method, it was necessary for the metrics to be determined by experimentation. Tests on a dynamic test gas stream facility were necessary for the inclusion of sampling. A particular challenge was presented at this point by the concentration range of only a few micrograms per cubic metre (µg/m³) which was to be attained for the individual components in the test gas, and by the variation, in some cases considerable, in their physical and chemical properties.

Activities/Methods:

Tests for determining the method metrics were conducted by means of the large test gas stream facility at the BGIA Institute for Occupational Safety and Health of the German Social Accident Insurance. These metrics included for example the reproducibility of the measurement results, recovery, and storage stability under a range of ambient conditions such as temperature and atmospheric humidity. The substances n-dodecane, R(+)limonene, toluene, p-xylene, hexanal, n-butyl acetate, octamethylcyclotetrasiloxane, 2-butoxyethanol, 2-ethyl-1-hexanol and 2-phenoxyethanol were selected as representative substances and produced in various concentration ranges. Different dispensing methods were required according to the volatility of the compound: a continuous-feed syringe dispenser was employed for dispensing the higher-volatility substances; substances of lower volatility were vaporized in a capillary evaporator.

Results:

The first step within this project involved optimized manufacture of test gas mixtures in a concentration range of approximately 10 to 150 µg/m³ per individual component.
The reproducibility of the measurement results for VOCs on the test gas stream was in the range from 1% to 5% for all substances under all conditions.
The variation coefficient of the method calculated from the calibrations lies between 1% and 3%.
The desired limit of detection of < 5 µg/m³ at a sampling volume of 2 l was attained for all substances.
The relative atmospheric humidity was varied within a range from 10% to 80%. No influence was detected.
Storage tests showed that storage of the sample carrier was possible for four weeks, with the exception of hexanal (two weeks).
The method is to be published in the BGIA Folder as a tested and recommended measurement method.

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