Xianjiang Li

Online Coupling of In-Tube Solid-Phase Microextraction with Direct Analysis in Real Time Mass Spectrometry for Rapid Determination of Triazine Herbicides in Water Using Carbon-Nanotubes-Incorporated Polymer Monolith

Online coupling of in-tube solid phase microextraction (IT-SPME) with direct analysis in real time mass spectrometry (DART-MS) was realized for the first time and applied in the analysis of triazine herbicides in lake water and orange juice. We incorporated single-wall carbon nanotubes (SWNTs) into a polymer monolith containing methacrylic acid (MAA) and ethylene dimethacrylate (EDMA) to form a novel poly(methacrylic acid-co-ethylene dimethacrylate-co-single wall carbon nanotubes) (poly(MAA-EDMA-SWNT)) monolith, which was then used in IT-SPME for enrichment of six triazine herbicides from water samples. With the online combination of IT-SPME with DART-MS, the analytes desorbed from the monolith were directly ionized by DART and transferred into MS for detection, thus rapid determination was achieved. Compared with regular DART-MS method, this online IT-SPME-DART-MS method was more sensitive and reproducible, because of the IT-SPME procedures and the isotope-labeled internal standard used in the experiment. Six triazine herbicides were determined simultaneously using this method with good linearity (R(2) > 0.998). The limit of quantification (signal-to-noise ratio of S/N = 10) of the six herbicides were only 0.06-0.46 ng/mL. The proposed method has been applied to determine triazine herbicides in lake water and orange juice, showing satisfactory recovery (85%-106%) and reproducibility (relative standard deviation of RSD = 3.1%-10.9%).

Online Coupling of Capillary Electrophoresis with Direct Analysis in Real Time Mass Spectrometry

The online coupling of capillary electrophoresis with ambient direct analysis in real time mass spectrometry (DART-MS) was realized by a coaxial tip interface. The analytes eluted from capillary electrophoresis (CE) were directly ionized by the metastable helium flux produced by DART and transferred into MS for the detection, with which the online separation and simultaneous detection were achieved. The CE-DART-MS can tolerate higher concentrations of detergents and salts than traditional CE-electrospray ionization (ESI)-MS and avoided the difficulties of collecting CE effluent and cleaning the interface, which simplified the experimental procedures and shortened the analysis time. The performance of the technique was successfully verified by capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography (MEKC) using a mixture of 4-aminoantipyrine, zolmitriptan, and quinine. This online technique showed good repeatability with the relative standard deviations (RSDs; n = 5) of 0.56-1.23% for the retention times and 2.01-7.41% for the peak areas. The quantitative analysis of 4-aminoantipyrine was accomplished in the range of 0.01-0.50 mg/mL with the linear correlation coefficient of 0.9995 and limit of detection of 14.7 fmol. Compared with CE-ESI-MS, the ion suppression effects of nonvolatile salts and detergents were efficiently minimized. The signal intensity remained constant when the concentrations reached 100 mM for sodium borate and 30 mM for SDS (in 30 mM sodium borate buffer). In addition, the proposed method was successfully applied to the detection of the endogenous caffeine in Chinese white tea.

Recent advances in applications of nanomaterials for sample preparation

Sample preparation is a key step for qualitative and quantitative analysis of trace analytes in complicated matrix. Along with the rapid development of nanotechnology in material science, numerous nanomaterials have been developed with particularly useful applications in analytical chemistry. Benefitting from their high specific areas, increased surface activities, and unprecedented physical/chemical properties, the potentials of nanomaterials for rapid and efficient sample preparation have been exploited extensively. In this review, recent progress of novel nanomaterials applied in sample preparation has been summarized and discussed. Both nanoparticles and nanoporous materials are evaluated for their unusual performance in sample preparation. Various compositions and functionalizations extended the applications of nanomaterials in sample preparations, and distinct size and shape selectivity was generated from the diversified pore structures of nanoporous materials. Such great variety make nanomaterials a kind of versatile tools in sample preparation for almost all categories of analytes.

Solid-phase extraction with the metal-organic framework MIL-101(Cr) combined with direct analysis in real time mass spectrometry for the fast analysis of triazine herbicides †

MIL-101(Cr) is an excellent metal-organic framework with high surface area and nanoscale cavities, making it promising in solid-phase extraction. Herein, we used MIL-101(Cr) as a solid-phase extraction packing material combined with fast detection of direct analysis in real time mass spectrometry (DART-MS) for the analysis of triazine herbicides. After systematic optimization of the operation parameters, including the gas temperature of DART, the moving speed of the 1D platform, solvent for desorption, amount of MIL-101(Cr) extraction time, eluent volume and salt concentration, this method can realize the simultaneous detection of five kinds of triazine herbicides. The limits of detection were 0.1∼0.2 ng/mL and the linear ranges covered more than two orders of magnitude with the quantitation limits of 0.5∼1 ng/mL. Moreover, the developed method has been applied for the analysis of lake water samples and the recoveries for spiked analytes were in the range of 85∼110%. These results showed that solid-phase extraction with metal-organic frameworks is an efficient sample preparation approach for DART-MS analysis and could find more applications in environmental analysis.

Applications of homochiral metal-organic frameworks in enantioselective adsorption and chromatography separation.

Chiral separation is of great importance for drug development, pharmacology, and biology. Chiral metal‐organic frameworks (MOFs) is a new class of porous solid materials with high surface area, large pore size, high chemical stability, uniformly structured cavities, and the availability of modification. The excellent properties of MOFs have attracted intense interest to explore their performance and mechanism in chiral separation. This review summarizes three synthetic strategies of chiral MOFs and their applications in enantioselective adsorption and chromatographic separation. All the experimental and molecular simulation results demonstrated that high enantioselectivity was strongly correlated with a close match between the size of the pore and chiral molecules.

Interface for Online Coupling of Surface Plasmon Resonance to Direct Analysis in Real Time Mass Spectrometry

The online coupling of surface plasmon resonance (SPR) with mass spectrometry (MS) has been highly desired for the complementary information provided by each of the two techniques. In this work, a novel interface for direct and online coupling of SPR to direct analysis in real time (DART) MS was developed. A spray tip connected with the outlet of the SPR flow solution was conducted as the sampling part of the DART-MS, with which the online coupling interface of SPR-MS was realized. Four model samples, acetaminophen, metronidazole, quinine, and hippuric acid, dissolved in three kinds of common buffers were used in the SPR-DART-MS experiments for performance evaluation of the interface and the optimization of DART conditions. The results showed consistent signal changes and high tolerance of nonvolatile salts of this SPR-MS system, demonstrating the feasibility of the interface for online coupling of SPR with MS and the potential application in the characterization of interaction under physiological conditions.

Direct Analysis in Real Time Mass Spectrometry: a Powerful Tool for Fast Analysis

Direct analysis in real time mass spectrometry (DART-MS) is one of the variants of ambient mass spectrometry. The ionization process of DART-MS is in open environment and only takes few seconds, so it is suitable for fast analysis. Actually, since its introduction in 2005, more and more attentions have been drawn to its various applications due to its excellent proper- ties, e.g., fast analysis, and no or less sample preparation, high salt tolerance and so on. This review summarized the promising features of DART-MS, including its ionization mechanism, equipment modification, wide applications, coupling techniques and extraction strategies before analysis.

Cysteine-Functionalized Metal–Organic Framework: Facile Synthesis and High Efficient Enrichment of N-Linked Glycopeptides in Cell Lysate

Cysteine-functionalized metal-organic framework (MOF) was synthesized via a common and facile two-step method of in situ loading of Au nanoparticles on amino-derived MOF followed by l-cysteine (Cys) immobilization. Owing to the large specific surface area and ultrahigh hydrophilicity of this nanocomposite, excellent performance was observed in the enrichment of N-linked glycopeptides in both model glycoprotein and HeLa cell lysate. By using this nanocomposite, 16 and 31 glycopeptides were efficiently extracted from digest of horseradish peroxidase (HRP) and human serum immunoglobulin G (IgG), respectively. The short incubation time (5 min), large binding capacity (150 mg/g, IgG digest to material), good selectivity (1:50, molar ratio of IgG and bovine serum albumin (BSA) digest), high recovery (over 80%), and low detection limit (1 fmol) ensure the effectiveness and robustness of MIL-101(NH2)@Au-Cys in complex HeLa cell lysate. As a result, 1123 N-glycosylation sites corresponding to 1069 N-glycopeptides and 614 N-glycoproteins were identified from the lysate. Compared with those of previously reported hydrophilic methods, to our knowledge, it was the best result. This work paves a new way for fast functionalization of MOF and also provides a novel idea for material design in sample preparation, especially in glycoproteome and related analysis.

Graphene matrix for signal enhancement in ambient plasma assisted laser desorption ionization mass spectrometry.

In this work, the signal intensity of ambient plasma assisted laser desorption ionization mass spectrometry (PALDI-MS) was significantly increased with graphene as matrix. The graphene functions as a substrate to trap analytes, absorb energy from the visible laser irradiation and transfer energy to the analytes to facilitate the laser desorption process. The desorbed analytes are further ionized by helium plasma and analyzed by MS. Compared with a traditional organic matrix, α-cyano-4-hydroxycinnamic acid (CHCA), graphene exhibited much higher desorption efficiency for most of the compounds benefitting from the strong optical absorption at 532nm. The performance has been confirmed by the facile analysis of more than forty compounds with various structures. Additionally, this method was successfully applied to distinguish three kinds of Chinese tea leaves by detecting the endogenous caffeine and theanine, which proved the utility, facility and convenience of this method for rapid screening of main components in real samples.

Study on the interaction of uranyl with sulfated beta-cyclodextrin by affinity capillary electrophoresis and molecular dynamics simulation.

The study on sulfated beta‐cyclodextrin binding to uranyl ion helps to get a better understanding of uranyl compounds’ intermolecular interaction mechanism and facilitates the structure‐based design of uranyl binding molecules. Here we investigated the electromigration of the inclusion complex by using affinity capillary electrophoresis in acidic solution. The binding constant was determined to be logK = 2.96 ± 0.02 (R2 = 0.996) through nonlinear regression approach. The possible configurations and structural features of the inclusion complex were further studied by molecular dynamics simulation. The results suggest the distinctions of coordination environment and hydration compared with bare uranyl ion in aqueous solution. Thus, two water oxygen atoms coordinated with uranyl in the first hydration shell at 2.55 angstrom instead of five in the same distance range. The binding free energy was calculated as –12.10 ± 1.46 kcal/mol by means of thermodynamic perturbation method. The negative value indicates that the process of S‐β‐CD capture uranyl ion in the aqueous media is spontaneous.