Development of strategies for the detection, extraction, and recovery of aqueous anions using highly selective redox-recyclable materials

Highly selective redox-recyclable materials were prepared by physisorbing the redox active extractant HEP+NO3 - [HEP = 1,1',3,3'-tetrakis(2-methyl-2-hexyl)ferrocene] onto various polymeric supports including polyesters and polystyrenes. The new materials were evaluated for their effectiveness towards the extraction of ReO4- and CnF2n + 1SO 3- (PFS) ions from a variety of aqueous solutions. The effects of coverage and size of the tetraalkylated ferrocenium cation were evaluated as well as the effectiveness over several redox cycles. The materials were also evaluated for their selectivity under a variety of conditions including contact time, pH, and concentration of a competing ion. The materials were found to be highly selective towards both ReO4- and PFS ions and were stable over several extraction-deactivation/recovery-reactivation cycles. A spectrophotometric assay, based on the selective exchange of a colorless PFS anion for a highly colored anion, was developed. The assay is quantitative and shows a linear response between 50 and 275 mug L-1 for one formulation of an aqueous film forming foam (AFFF) concentrate. A negative-ion-electrospray mass spectrometric method was developed for the detection and identification of fluorinated surfactants. The method was able to achieve a detection limit of 6 mug L-1 for the AFFF concentrate. Quantification and identification information was achieved by using an internal standard with a similar sensitivity coefficient to the PFS anions. Enhancement in sensitivity of an attenuated-total-reflectance (ATR) FTIR spectrometer for IR-active anions in aqueous solutions by physisorbing organometallic extractants to the surface of the ATR probe was investigated. A thin film of 1,3-bis(diphenylphosphino)propanedichloronickel(II) applied to the tip of the ATR probe was used to detect aqueous CN- in the low microgram per liter (ppb) concentration range. The detection limit with the film was 5 mug L-1 CN-. Applying a thin film of 1,1',3,3'-tetrakis(2-methyl-2-nonyl)ferrocenium nitrate afforded a sensitivity increase of 96,000 for ClO4 - and 4,000 for C8F17SO3 -. The detection limits reported here are unprecedented for infrared detection of these ions in aqueous solutions.