Investigating the applicability of a thermal extraction method for the quantification of dimethylformamide (DMF) in work gloves

Status:

completed 03/2015

Aims:

Residues of dimethylformamide (DMF) can remain in the final product during the production of polymer-based work gloves (e.g. using polyurethane). The extractive determination of such DMF content, e.g. using solvent extraction with methanol, is limited in its sensitivity due to the inevitable dilution of the target compound. Thermal volatilization of DMF (thermal extraction) and accumulation of the compound on a suitable adsorbent avoids these dilution effects. For these reasons, thermal extraction should feature a higher sensitivity than solvent extraction. Aim of this project was testing and optimization of a thermal extraction method for a series of common work gloves.

Activities/Methods:

- Analysis of dimethylformamide (DMF) performed via gas chromatography coupled with mass spectrometry - Samples of work gloves extracted via solvent extraction and thermal extraction - Collection of thermally released DMF on a feasible sorbent and thermally desorbed before analysis. - Assessing and comparing of the method uncertainties - Further work packages based on the systematic variation of thermal extraction parameters (temperature, sorbent, gas flow) and the influence of sample preparation.

Results:

The key conclusions of this project are: - Thermal extraction is feasible to determine DMF contents below 1 mg/kg in work gloves. - The liquid extraction performed in this project featured a limit of determination of 24 mg/kg and a limit of detection of 8 mg/kg. - Tenax TA is a suitable adsorbent for the accumulation of DMF from work gloves. - During sampling and analysis several splits are necessary for the quantification of DMF on the adsorbent in order to prevent overloading of the analytical system or the sampling phase with co-extracted compounds. - Thermal extraction at 150 ° C for 40 min provided sufficient extraction efficiency. - If the work glove sample contains significant residues of water, DMF can be mobilized from the adsorbent which cannot be compensated by the internal standard. This enforces the necessity of statistical supervision of the parameters of the analytical system (e.g. quality control chart). - In principle, the assessment of the determined contents has to be based on the extraction of complete work gloves. Such measurements are possible at moderate effort using thermal extraction and they eliminate possible influences of cutting. - Cutting has a negligible influence in case of optically uniform samples. If the glove contains different materials the DMF-containing component must be representatively present in the sample. - Half of the sample collective that have been analyzed within the framework of this project featured DMF contents below 10 mg/kg. - The expected product-specific variability of the DMF content in individual samples was observed during the thermal extraction of complete work gloves and pre-cut samples. - Solvent extraction and thermal extraction feature a good correlation for DMF contents below 30 mg/kg. The observed deviations at higher contents might be caused by the variability in the material samples. - Like in case of the methanol extraction, thermal extraction measurements require multiple measurements to derive statistically assured results. The performed project proved that the extraction of complete work gloves for checking the compliance to existing limit values is analytically possible at moderate effort. Thermal extraction is more sensitive but – in case of insufficient dilution during sampling – vulnerable against elevated residual moisture in the material. Therefore, the thermal extraction method demands for strict quality assurance measures in the respective test lab (e.g. statistical observation of instrument parameters). Since work gloves can be inhomogeneous samples, test standards are necessary in order to get comparable results for each type of extractive analysis. However, a general uncertainty on the results has to be tolerated due to the present product-specific variability which is independent of the applied analytical technique.

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