Abstract
The composition of impurities in perfluorooctanoic acid (PFOA) was measured and determined to be notably different between lots. Since the purity of PFOA varied, the accuracy of prepared calibration solution concentrations was reduced. In this study, factors influencing the purity were investigated using a Karl Fischer titrator and a LC/MS to support the development of reference materials. The results showed variances of water and isomer/homologue contents under different ambient conditions during sample handling. Moreover, these variances, especially for water, greatly affected the purity of PFOA (0.95–0.99 kg kg−1). Therefore, PFOA of reliable purity should be used for the preparation of calibration solutions.
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Appendix
Appendix
Homogenization of PFOA
Chipped particles of linear PFOA (Chemical Analysis grade, lot: PEH6950) were homogenized to use for testing. The commercial PFOA stood at room temperature in a laboratory atmosphere for 4 weeks with occasional mixing. Homogenized PFOA (net amount = 50 mg) was divided into 70 vials in the laboratory. Divided vials were kept at approximately 4 °C and shielded from light.
Between-vial homogeneity of the divided PFOA was estimated by determining the \( w_{{{\text{H}}_{2} {\text{O}}}} \) and peak area percentages of perfluorooctanoate relative to total peak area in three subsamples that were taken from five randomly selected vials (Nos. 1, 18, 35, 52, and 70) out of 70 vials using a KFT and a LC/MS, respectively. In total, 15 homogeneity samples were used for each measurement. Technically invalid results were removed, and then analysis of variance (ANOVA) of data was performed based on ISO Guide 98-3. The standard deviations between the vials (s bb) were calculated. If the repeatabilities of the measurement methods were insufficient, the influences of the measurement variations on the standard deviations between units (u bb) were also calculated. In this study, the u bb was greater than the s bb, so the u bb was considered as the uncertainty of the homogeneity in both the \( w_{{{\text{H}}_{2} {\text{O}}}} \) and the peak area percentages. Obtained results were not significant at 0.05 (0.2 g kg−1 for the \( w_{{{\text{H}}_{2} {\text{O}}}} \) and 0.03 % for the peak area percentages). Therefore, homogeneity of the divided PFOA was sufficient for evaluation of a relationship among the purity of PFOA, the \( w_{{{\text{H}}_{2} {\text{O}}}} \), etc.
Monohydrate calculations
The molar mass of PFOA is approximately 414 g mol−1, while the molar mass of PFOA monohydrate is approximately 432 g mol−1 (PFOA 414 g mol−1; H2O 18 g mol−1). Therefore, the mass fraction of water in PFOA monohydrate is approximately 4.2 % or 42 g kg−1 (18/432). Similar calculations for PFNA lead to 18/(464 + 18) ≃ 3.7 % and hence to 37 g kg−1 while for PFDA monohydrates we arrive at 18/(514 + 18) ≃ 3.4 % and hence at 34 g kg−1.
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Hanari, N., Itoh, N., Yamazaki, T. et al. Influence of desorption and sorption of water on the purity of perfluorooctanoic acid. Accred Qual Assur 18, 137–142 (2013). https://doi.org/10.1007/s00769-013-0958-y
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DOI: https://doi.org/10.1007/s00769-013-0958-y