Na Yang,Keting Li,Yufan Hao,Longfei Zhang,Yongli Sun,Luhong Zhang,Bin Jiang
Polyethyleneimine (PEI) nanofiltration (NF) membranes hold great application prospects in lithium extraction from salt lakes due to their high positive charge properties. However, the poor permeability of the membranes caused by the dense separation layer structure severely hinders their further application. Herein, a functional end-capping strategy was employed to address this problem by adding the effective end-capping reagent, Girard's Reagent T (GRT), to the PEI aqueous phase as the co-reaction reagent. Under the dual functions of the end-capping effect and the quaternary ammonium groups of GRT, the looseness and positive charge of the membrane were simultaneously optimized. After the modification of GRT, the looser structure of the PEI/GRT NF membrane improved its pure water flux (PWF) to 115 L m −2 h −1 at 6 bar, which was around 3.7 times higher than that of the original PEI NF membrane. Meanwhile, the enhanced positive charge (from −8 to 9 mV, pH = 7) of the membrane bottom surface allowed it to maintain the high rejection rate of MgCl 2 at 97.2 %. Besides, the PEI/GRT NF membrane exhibited good Mg 2+ /Li + selectivity (S Mg 2+ /Li + = 22.7, 2000 ppm, Mg 2+ /Li + mass ratio: 20:1). Therefore, this study provides a simple and feasible strategy for the preparation of high-permeable PEI NF membranes with good Mg 2+ /Li + separation performance.
Sensitive glycomics analysis by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) is of great importance but significantly hampered by their low ionization efficiency and labile sialic acid moieties. Chemical derivatization offers a viable way to improve both the ionization efficiency and analytical sensitivity of the glycans in MS analysis by altering their hydrophobicity or charge property. Here we employed Girard's reagent T (GT) for on-target derivatization (GTOD) of reducing glycan under mild acid condition to form stable hydrazones at room temperature , allowing rapid and sensitive identification of neutral and sialylated glycans in positive-ion mode as only permanently positive charged molecular ions without multiple ion adducts by MALDI-TOF-MS. The MS signal intensities of lactose, sialylated N-glycans derived from bovine fetuin and neutral N-glycans derived from RNaseB and ovalbumin were boosted by 7.44, 9.13, 12.96 and 13.47 folds on average (n = 3), respectively. More importantly, after GTOD strategy, unwanted desialylation of sialylated glycans during MS was suppressed. The detection limit of the assay is desirable since the nanogram of N-glycans derived from 0.16 μg ovalbumin could be detected. The assay demonstrated good stability (RSD≤2.95%, within 10 days), reliable reproducibility (RSD = 2.96%, n = 7) and a desirable linear dynamic range from 78 nmol/mL to 10 μmol/mL. The strategy has been successfully applied to MS analysis of reducing glycans from human milks, neutral and sialylated O-, N-glycans from glycoproteins , and reducing glycans derived from glycosphingolipids , presenting neater [M] + signals which allow detection of more low-abundance glycans and assignation of Neu5Ac vs. Neu5Gc or fucose vs. hexose in glycans due to the absence of the ambiguous interpretation from multiple peaks (ion adducts [M+Na] + and [M+K] + ). Moreover, the GTOD assay prevents desialylation during MALDI-TOF-MS profiling and enables distinct linkage-specific characterization of terminal sialic acids of N-glycans derived from human serum protein when combines with an esterification .
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