Recent analytical applications of fluorinated hydrocarbon-based stationary phases in HPLC

Superhydrophobic fluorinated microspheres for fluorous affinity chromatography

Fluorous affinity chromatography has received growing attention in separation and purification of fluoro compounds, but the wettability of the fluorinated stationary phases is seldom noticed. Here, we construct a series of micro-sized fluorine-containing microspheres by solvothermal precipitation polymerization. The fluorinated microspheres could be obtained with narrow size distribution at even high monomer loading of 15 wt%. Through alternating fluoro monomer, both the particle size and the wettability of the microsphere array could be tuned. Among them, the poly(divinylbenzene -dodecafluoroheptyl methacrylate), P(DVB-DFHMA), microsphere (6.1 μm) arrays displays superhydrophobicity with 153.2° water contact angle. The P(DVB-DFHMA) fluorinated microspheres (7.58% fluorine content) can be packed into steel-less columns as stationary phase for high-performance liquid chromatography. The retention mechanism of the fluorinated column is proven to be the specific fluorine-fluorine interaction. Compared to the commercial C18 silica column, the fluorinated column can completely separate fluorine-containing compounds under high water content mobile phase, including small fluoro molecules and fluoro macromolecules, at much lower back pressure by fluorous affinity.

High-performance liquid chromatography quantitative analysis of ephedrine alkaloids in Ephedrae Herba on a perfluorooctyl stationary phase

Ephedrae Herba is one of the most commonly used herbal medicines, and it has been shown that most of the clinical efficacy for cold and asthma is exerted by its alkaloidal components. A simple and sensitive high-performance liquid chromatography method was developed using a perfluorooctyl column for the simultaneous determination of five alkaloids (norephedrine, norpseudoephedrine, ephedrine, pseudoephedrine, and methylephedrine) in Ephedrae Herba. The mobile phase comprising acetonitrile and 15 mM ammonium trifluoroacetate was used to elute the targets in isocratic elution mode. The method was validated for linearity (R²  > 0.999), repeatability, intraday and interday precision, recoveries with trueness (93.87-110.99%), limits of detection (5.35-5.76 µg/mL), and limits of quantification (20 µg/mL). The quantitative results revealed that the developed method was precise and accurate. Then it was successfully applied to determine the difference in the contents of three batches of Ephedrae Herba from three pharmaceutical companies.

Analysis of fluorinated compounds by micellar electrokinetic chromatography - mass spectrometry

Micellar electrokinetic chromatography (MEKC) is a good separation technique with high efficiency, high selectivity and simple preparation process. Hyphenation of MEKC with mass spectrometry (MS) could extend its application in complex sample analysis. However, direct coupling MEKC using commonly used surfactants like sodium dodecyl sulfate (SDS) with ESI-MS will lead to strong signal suppression. In this work, a MEKC-MS method using volatile ammonium perfluorooctanoate as surfactant was developed. The MS compatibility of ammonium perfluorooctanoate was investigated. The result revealed that there is no signal suppression even the concentration of ammonium perfluorooctanoate was up to 300 mM. Meanwhile, we found that ammonium perfluorooctanoate used as surfactant in MEKC provided powerful F-F interaction and hydrophobic interaction, which was beneficial for separation of fluorinated compounds. Using the ammonium perfluorooctanoate based MEKC method, several groups of fluorinated compounds, which cannot be separated using non-fluorinated surfactants like lauric acid and SDS based MEKC method, were baseline separated. Finally, the MEKC-ESI-MS method was successfully applied for analysis of two herbicides including fluometuron and fenuron in lake water samples with high separation efficiency, high sensitivity, good linearity and reproducibility.

Elucidation of the Molecular Determinants for Optimal Perfluorooctanesulfonate Adsorption Using a Combinatorial Nanoparticle Library Approach

Perfluorooctanesulfonate (PFOS) persistently accumulates in the environment and in humans, causing various toxicities. To determine the key molecular determinants for optimal PFOS specificity and efficiency, we designed and synthesized a combinatorial gold nanoparticle (GNP) library consisting of 18 members with rationally diversified hydrophobic, electrostatic, and fluorine-fluorine interaction components for PFOS bindings. According to our findings, the electrostatic and F-F interactions between PFOS and nanoparticles are complementary. When F-F attractions are relatively weak, the electrostatic interactions are dominant. As F-F interactions increase, the electrostatic contributions are reduced to as low as 20%, demonstrating that F-F binding may overpower even electrostatic interactions. Furthermore, F-F interactions (28-79% binding efficiency) are 2-fold stronger than regular hydrophobic interactions (15-39% binding efficiency) for PFOS adsorption, explaining why these novel PFOS-binding nanoparticles are superior to other conventional materials based on either hydrophobic or electrostatic binding. The PFOS adsorption by the optimized nanoparticles performs well in the presence of ionic interferences and in environmental wastewater. This library mapping approach can potentially be applied to recognition mechanism investigation of other pollutants and facilitate the discovery of effective monitoring probes and matrices for their removal.