Effects of inorganic ions with different concentrations on the nanofiltration separation performance of perfluorobutane sulfonic acid (PFBS).

Perfluorobutane sulfonic acid (PFBS) is a kind of anthropogenic recalcitrant contaminant that has posed a threat to drinking water safety and brought widespread public health concerns. Nanofiltration (NF) is an effective way to remove PFBS from drinking water, while the removal is influenced by coexisting ions. To investigate the effects and intrinsic mechanisms of coexisting ions on the rejection of PFBS, poly(piperazineamide) NF membrane was utilized in this work. Results showed that most cations and anions in the feedwater could effectively improve PFBS rejection and simultaneously reduce NF membrane permeability. In most cases, the decrease in NF membrane permeability corresponded to an increase in the valence of cations or anions. When cations (Na+, K+, Ca2+, and Mg2+) were present, the rejection of PFBS was effectively improved from 79% to more than 91.07%. Under these conditions, electrostatic exclusion was the dominant NF rejection mechanism. This was also the leading mechanism for 0.1 mmol/L Fe3+ coexisted condition. As the concentration of Fe3+ increased to 0.5-1 mmol/L, intensified hydrolyzation would accelerate the formation of the cake layers. The differences in the cake layer characteristics led to the different rejection trends of PFBS. For anions (SO42- and PO43-), both sieving effects and electrostatic exclusion were enhanced. As anionic concentration raised, the NF rejection of PFBS increased to above 90.15%. By contrast, the effect of Cl- on PFBS rejection was also affected by coexisting cations in the solution. The dominant NF rejection mechanism was electrostatic exclusion. Accordingly, it is suggested that the usage of negatively charged NF membranes could facilitate the efficient separation of PFBS under ionic coexisting conditions, thereby ensuring the safety of drinking water.

Integrated microfluidic chip for on-line proteome analysis with combination of denaturing and rapid digestion of protein.

A microfluidic platform based on the integration of denaturation and online immobilized enzyme reactor (IMER) digestion for protein pretreatment was first developed on a glass chip. The design of three inlet channels and two groups of snake channel in glass chip can allow the protein solution, the reducing reagent and the alkylating agent to be simultaneously injected into the chip channel and ensured the reaction solution on-line efficient mixing and sufficient reacting. By thiol-ene click chemistry, the capillary-based and glass chip-based trypsin IMER on the surface of poly(trimethylolpropane trimethacrylate) monolith were fabricated. The wide range of flow rate tolerance (0.8-5.0 µL/min), and the acceptable reproducibility (RSD% = 3.1%, n = 5) and stability (13.8% decrease of enzyme activity in 2 months) indicated the feasibility of using IMER for online digestion of proteins. Compared with the solution denaturation-offline IMER digestion, the integrated microfluidic platform of chip denaturation-chip IMER and chip denaturation-online IMER have comparable protein identification ability for mouse liver protein with a similar number of protein (798 or 826 vs. 843) and unique peptides (3923 or 4593 vs. 3916). More importantly, the easy and fast digestion of protein samples and possible combination with MS revealed that this microfluidic platform can be a potential method for rapid proteomics analysis.

Green synthesis of monolithic enzyme microreactor based on thiol-ene click reaction for enzymatic hydrolysis of protein.

In this study, a monolithic enzyme reactor based on a strategy of green synthesis was successfully prepared in a capillary with trypsin immobilized by "thiol-ene" click reaction. A polymer of poly(butyl methacrylate-co-α-methacrylic acid-co-ethylene glycol dimethacrylate) was prepared in a mixture of 1-butyl-3-methylimidazolium tetrafluoroborate and choline chloride/ethylene glycol as the support of enzyme reactor. After "thiol-ene" reaction was used for enzyme immobilization, the Michaelis constants and maximum reaction rate of the resulting immobilized enzyme reactors (IMER) were determined by capillary electrophoresis to be 2.1 mmol/L and 0.028 µmol/min, respectively. The enzymatic hydrolysis of the enzyme reactor under different experimental conditions were investigated. A on-line digestion of bovine serum albumin (BSA) on the new IMER can be achieved within 50 s, up to 864 times faster than in-solution digestion (12 h). BSA can be well digested and the numbers of identified peptides were 73 with the coverage rates of 82.7%. The IMER was further used for the analysis of protein extracts from rat liver, and 1034 protein groups were identified. All these results demonstrated that such a click reaction based IMER would be of great prospect in the high throughput analysis for proteome with high confidence.