Influence of desorption and sorption of water on the purity of perfluorooctanoic acid

Evaluation of perfluorooctanoic acid purity based on potentiometric titration

“…Moreover, evaluating the reliable purity of PFOA used for solution preparation is essential as it affects the nal concentration. According to our previous report, 6 the purity of PFOA varied due to different ambient conditions during sample handling because PFOA is a hygroscopic substance. 1 The reliability of purity of PFOA is required for the quality assurance of analyses.…”

“…9 However, this technique did not satisfy the requirements for reliable purity evaluation of linear PFOA because this compound is a detergent and hygroscopic, and repeatedly adsorbed and desorbed water as an impurity under different ambient conditions during sample handling. 6 Then, we focused on titrimetry, regarded as one of the primary techniques of measurements, 7,8 to evaluate the reliable purity of PFOA because PFOA is a monovalent acid. However, some problems must be solved to achieve accurate titration on purity evaluation, such as the hygroscopicity 6 and poor solubility 1 of PFOA.…”

“…6 Then, we focused on titrimetry, regarded as one of the primary techniques of measurements, 7,8 to evaluate the reliable purity of PFOA because PFOA is a monovalent acid. However, some problems must be solved to achieve accurate titration on purity evaluation, such as the hygroscopicity 6 and poor solubility 1 of PFOA. We have found the conditions to prepare the homogenous linear PFOA with stable purity by referring to our previous report.…”

“…We have found the conditions to prepare the homogenous linear PFOA with stable purity by referring to our previous report. 6 Moreover, we have changed the titration solvent from water to aqueous NaOH to improve the solubility. In addition, analytical results based on the neutralization potentiometric titration using a potentiometric titrator (PT) were compared with the results based on the mass balance technique 10,11 in combination with a LC/MS, Karl-Fischer titrator (KFT), etc.…”

“…The procedure for homogenization of both PFOA reagents is detailed elsewhere. 6 Aqueous NaOH solutions (0.05 and 0.01 mol L À1 ) used for PT analyses, innity pure grade acetonitrile (ACN), ACN for LC/MS analysis and analytical grade ammonium acetate as the buffer were also obtained from Wako Pure Chemical Industries. Peruoroheptanoate (PFHpA) and peruorononanoate (PFNA) were obtained from Fluorochem (Old Glossop, England, UK).…”