Determination of perfluorinated carboxylic acids in water using liquid chromatography coupled to a corona-charged aerosol detector

Sub-ppm determination of perfluorinated carboxylic acids in solution by UV-vis high-performance liquid chromatography through solid phase extraction

This study investigated a novel and sensitive analytical method based on a simple heat-based derivatization using 3-bromoacetyl coumarin as the reagent and analysis with a HPLC-UV system or just a UV-vis spectrometer to allow the sub-ppm determination of PFCAs in water solution with the potential for utilization in simple laboratories and field laboratory scenarios. A Strata-X-AW cartridge was used for the solid phase extraction (SPE) procedure and higher than 98% recoveries were obtained. The derivatization condition showed that a high efficiency of peak separation was obtained with obviously different retention time among various PFCAs derivatives using HPLC-UV analysis. The derivatization stability and repeatability showed favorable results with stable derivatized analytes for ≤12 h and a relative standard deviation (RSD) of <2% for all repetitions. The limit of detection for the HPLC-UV analysis was between 0.1 ppm and 0.5 ppm. A satisfactory linearity response was found with R² >0.998 for all individual PFCA compounds. The limit of detection for simple UV-Vis analysis was <0.0003 ppm to measure the presence of PFCAs. Contamination of standards with humic substances and measurement of industrial samples in a complex wastewater matrix showed no adverse effects on the accuracy of PFCA determination by using the developed methodology.

Superficially capped amino metal-organic framework for efficient solid-phase microextraction of perfluorinated alkyl substances

Perfluorinated alkyl substances (PFASs) were ubiquitously in the surface and groundwater. It is crucial and urgent to develop a rapid and ultrasensitive analysis method for the quantification of trace-level PFASs. Herein, a highly hydrophobic sorbent by capping phenylsilane groups on the surfaces of NH₂-UiO-66(Zr) nanocrystals was used for efficient solid-phase microextraction (SPME) of PFASs in water samples. It was found that the superficially capped nanocrystals (NH₂-UiO-66(Zr)-hp) exhibited both faster extraction kinetics and higher enrichment capacity than the non-capped nanocrystals. The extraction of eleven kinds of PFASs by NH₂-UiO-66(Zr)-hp fiber reached equilibrium in 20 min. The enrichment factors of the NH₂-UiO-66(Zr)-hp fiber ranged from 6.5 to 48, with a preference for long-chain PFASs over short-chain PFASs. It was proposed that superficial capping eliminated competitive moisture adsorption on the surfaces of the non-capped nanocrystals, thus facilitating the adsorption of PFASs through hydrophobic interaction. By using this new sorbent, the limits of detection of the SPME method as low as 0.035 to 0.616 ng·L^-1 were achieved for the target PFASs. The recoveries of PFASs in the environmental water samples were 80.9%-120%. This study presents a new strategy for developing an efficient sorbent for PFASs by surface hydrophobic modification.

Complete Defluorination and Mineralization of Perfluorooctanoic Acid by a Mechanochemical Method Using Alumina and Persulfate

Perfluorooctanoic acid (PFOA) is a persistent organic pollutant that has received concerns worldwide due to its extreme resistance to conventional degradation. A mechanochemical (MC) method was developed for complete degradation of PFOA by using alumina (Al₂O₃) and potassium persulfate (PS) as comilling agents. After ball milling for 2 h, the MC treatment using Al₂O₃ or PS caused conversion of PFOA to either 1-H-1-perfluoroheptene or dimers with a defluorination efficiency lower than 20%, but that using both Al₂O₃ and PS caused degradation of PFOA with a defluorination of 100% and a mineralization of 98%. This method also caused complete defluorination of other C3∼C6 homologues of PFOA. The complete defluorination of PFOA attributes to Al₂O₃ and PS led to the weakening of the C-F bond in PFOA and the generation of hydroxyl radical (•OH), respectively. During the MC degradation, Al₂O₃ strongly anchors PFOA through COO^--Al coordination and in situ formed from Lewis-base interaction and PS through hydrogen bond. Meanwhile, mechanical effects induce the homolytic cleavage of PS to produce SO₄^•-, which reacts with OH group of Al₂O₃ to generate •OH. The degradation of PFOA is initiated by decarboxylation as a result of weakened C-COO^- due to Al³⁺ coordination. The subsequent addition of •OH, elimination of HF, and reaction with water induce the stepwise removal of all carboxyl groups and F atoms as CO₂ and F^-_, respectively. Thus, complete defluorination and mineralization are achieved.

Structure-based prediction of CAD response factors of dammarane-type tetracyclic triterpenoid saponins and its application to the analysis of saponin contents in raw and processed Panax notoginseng

Structure-based impacts of saponins on CAD response factors are discovered, and in-depth analysis of saponins in Panax notoginseng is implemented.

Simultaneous analysis of silicon and boron dissolved in water by combination of electrodialytic salt removal and ion-exclusion chromatography with corona charged aerosol detection

Selective separation and sensitive detection of dissolved silicon and boron (DSi and DB) in aqueous solution was achieved by combining an electrodialytic ion isolation device (EID) as a salt remover, an ion-exclusion chromatography (IEC) column, and a corona charged aerosol detector (CCAD) in sequence. DSi and DB were separated by IEC on the H(+)-form of a cation exchange resin column using pure water eluent. DSi and DB were detected after IEC separation by the CCAD with much greater sensitivity than by conductimetric detection. The five-channel EID, which consisted of anion and cation acceptors, cathode and anode isolators, and a sample channel, removed salt from the sample prior to the IEC-CCAD. DSi and DB were scarcely attracted to the anion accepter in the EID and passed almost quantitatively through the sample channel. Thus, the coupled EID-IEC-CCAD device can isolate DSi and DB from artificial seawater and hot spring water by efficiently removing high concentrations of Cl(-) and SO4(2-) (e.g., 98% and 80% at 0.10molL(-1) each, respectively). The detection limits at a signal-to-noise ratio of 3 were 0.52μmolL(-1) for DSi and 7.1μmolL(-1) for DB. The relative standard deviations (RSD, n=5) of peak areas were 0.12% for DSi and 4.3% for DB.