Yajun Zheng

Facile preparation of paper substrates coated with different materials and their applications in paper spray mass spectrometry

Direct application of available well-defined materials for mass spectrometry analysis represents a significant step in the combination of materials science and analytical chemistry. The present study introduces a facile vacuum filtration method for directly coating different commercially available materials onto the surface of filter paper. High sensitivity and quantitation precision have been demonstrated for different analytes including therapeutic drugs, proteins and volatile compounds in various matrices using the obtained papers as substrates for paper spray mass spectrometry.

Calcination temperature-dependent surface structure and physicochemical properties of magnesium oxide

Magnesium oxide (MgO), as an exceptionally important inorganic material, has been widely studied in view of its unique surface properties, but the correlation between its surface structure and physicochemical performance is still scarce. Here we report the evolution of the surface structure and physicochemical properties of trapezoid-like MgO microparticles with calcination temperature by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), thermal gravimetric analysis (TGA) and X-ray diffraction (XRD) techniques. The results demonstrated that along with the surface change of MgO from a smooth appearance to the structure composed of nanoparticles, its corresponding crystal structure evolved from mesocrystal to polycrystal, then to pseudomorph, and finally to cubic single crystal with the increase of calcination temperature ranging from 400 °C to 1000 °C. It also illustrated that the electrochemical capability of MgO was highly dependent on its crystal structure, whereas its catalytic activity had a good correlation with its textural properties (e.g., surface area and porosity) although the reaction selectivity was related to the calcination temperature. This work highlights the vital role of calcination temperature in determining the surface structure and physicochemical properties of the inorganic material MgO, which in turn will tailor its overall performance in the final applications.

One-pot synthesis of highly efficient MgO for the removal of Congo red in aqueous solution

Magnesium oxide (MgO) has been demonstrated to be a promising candidate for the treatment of toxic dyes in wastewater due to its unique characteristics (e.g., high isoelectric point, nontoxicity and cost-effectiveness). However, it is still a great challenge to fabricate highly efficient MgO for toxic dyes through facile synthetic strategies. Herein, a porous rod-like MgO with extremely high adsorption capacity for Congo red dye (3236 mg g−1) has been presented through a facile precipitation reaction between Mg2+ and CO32− in the presence of a trace amount of sodium silicate. After systematically investigating the experimental parameters, the results exhibited that the performance of the resulting MgO was very sensitive to the amount of sodium silicate in the reaction, stirring time and calcination temperature, and its adsorption capacity was closely related to the surface base properties rather than the specific surface areas of MgO. The adsorption process of Congo red on the as-synthesized product obeyed the pseudo-second-order rate equation and the Langmuir adsorption model. It is expected that the developed method will provide a facile route to gram level production of highly efficient MgO for handling toxic dyes in industrial wastewater.

Metal–organic framework coated paper substrates for paper spray mass spectrometry

Metal–organic frameworks (MOFs) have emerged as novel materials owing to their inherent structural characteristics, i.e., a large surface area and a well-ordered porous structure, but there are no reports on their application to paper spray mass spectrometry. Herein we explore the capability of paper substrates coated with three types of MOFs [e.g., MIL-53(Al), ZIF-8 and UiO-66(Zr)] for paper spray, in which the as-prepared UiO-66(Zr) coated paper demonstrated the highest sensitivity in the analysis of therapeutic drugs in dried blood spots relative to MIL-53(Al) and ZIF-8 coated paper substrates. To get a better understanding on the interactions between drugs and MOF coated papers, much effort has been focused on the elution behaviors of target drug verapamil from the MOF coated papers and the adsorption ability of the studied analyte to MOF particles in solution systems. Due to the more favorable elution behaviors and weaker adsorption ability of the tested drugs at the surface of UiO-66(Zr) coated paper relative to the other two papers, the estimated lower limit of quantitation (LLOQ) values of the examined drugs with UiO-66(Zr) coated paper have improvements of 8.5–46.6-fold relative to those from uncoated filter paper, and the values were in the range of 0.04–0.65 ng mL−1. Based on the high sensitivity of UiO-66(Zr) coated paper in drug quantitative analysis, the developed paper has also been successfully applied for the analysis of five anti-psychotic drugs (e.g., clozapine, amisulpride, quetiapine, risperidone and aripiprazole) in 40 human blood samples.

Controlled synthesis of mesocrystal magnesium oxide parallelogram and its catalytic performance

Mesocrystal magnesium oxide (MgO) parallelogram with lengths of diagonal line in the range of 7–9 μm has been synthesized through a facile precipitation method by using phosphate species as the morphology regulator and Mg(NO3)2 and Na2C2O4 as the inorganic sources. Scanning electronic microscope examination revealed that there is a canyon in the middle of the diagonal line of the as-synthesized products. The canyon resulted from the self-assembly of layer-like structures with a thickness of around 100–150 nm on both sides. To investigate the effect of reaction conditions on the morphologies and components of the resulting products, the types and addition amount of phosphate species and the reaction temperature were studied in detail. The results demonstrated that the introduction of trace amounts of phosphate species in the reaction system played a crucial role in determining the morphologies of the obtained products with variation of reaction temperatures, whereas their components have little been influenced after analyses by Fourier-transform infrared spectroscopy and X-ray diffraction. When as-synthesized mesocrystal MgO was employed as a catalyst in the Meerwein–Ponndorf–Verley (MPV) reaction between benzaldehyde and ethanol, it demonstrated superior performance to MgO particles without the presence of phosphate species.

Characterization of the surface properties of MgO using paper spray mass spectrometry.

RATIONALE Significant advances have been made in the preparation of different morphologies of magnesium oxide (MgO), but the relationship between MgO morphology and its interactions with therapeutic drugs is rarely studied. Herein, we investigated the interactions between different morphologies of MgO and therapeutic drugs using paper spray mass spectrometry. METHODS Different morphologies of MgO including trapezoidal, needle-like, flower-like and nest-like structures were prepared through a facile precipitation method. The as-obtained MgO particles were then coated onto the surface of filter paper via vacuum filtration strategy. The coated papers with different morphologies of MgO were used as the substrates for paper spray mass spectrometry to explore the interactions between different MgO and therapeutic drugs. RESULTS Through investigating the interactions between different morphologies of MgO coated papers and therapeutic drugs, it demonstrated that, in contrast to the trapezoidal, needle-like and nest-like MgO coated papers, different drugs in dried blood spots (DBS) were more favourably eluted off from the paper coated with flower-like MgO due to its weaker surface basicity. Also, the signal intensities of different drugs during paper spray were highly dependent on their elution behaviours. CONCLUSIONS Paper spray mass spectrometry (MS) provides an avenue to elaborate the surface properties of MgO with different structures. The surface basicity of MgO played a crucial role in determining the elution behaviours of therapeutic drugs in DBS, and a more favourable elution behaviour tended to result in a higher MS signal. Copyright

Ambient Ionization-Paper Spray Ionization and Its Application

Abstract Ambient ionization has gained increasing attentions in recent years due to its characteristics such as simplicity, high efficiency and without sample pretreatment prior to analysis. Although ambient ionization has got a considerable development and has been applied in diverse fields for rapid detection, high-throughput analysis of complex samples has put forward higher requirements to ambient ionization-mass spectrometry. Paper spray ionization source is a recently developed ambient ionization, which has demonstrated promising in high-throughput analysis of foodstuffs and drugs due to its facile operation, low-cost and simple separation in analysis. Herein, the development of paper spray ionization was comprehensively reviewed, and the basic principle, influencing factors, performance of paper spray and its application were highlights. Also, the advantages and disadvantages of this technique were discussed in detail followed by its development directions.

Morphological and surface structural evolutions of MgO particles from parallelograms to rods

The morphologies and surface structures of particles with different compositions are vital for determining their properties and applications. But the morphological and structural changes associated with the composition changes of MgO precursors and the physicochemical properties of the obtained MgO are barely studied. Herein we reported the morphology, surface structure and physicochemical property changes of MgO particles associated with the ratio of two basic precipitation reagents (Na2C2O4 and K2CO3) for the construction of MgO precursors. We also found that the physicochemical properties of the obtained MgO were closely related to the ratios of Na2C2O4 and K2CO3. When the ratio was 1 : 1, the generated MgO exhibited superior surface basicity and catalytic performance relative to others.

Sub-ppt Mass Spectrometric Detection of Therapeutic Drugs in Complex Biological Matrixes Using Polystyrene-Microsphere-Coated Paper Spray

Polystyrene (PS) is a class of polymer materials that offers great potential for various applications. However, the applications of PS microspheres in paper spray mass spectrometry are largely underexplored. Herein we prepared a series of PS microspheres via a simple dispersion polymerization and then used them as coating materials for paper spray mass spectrometry (MS) in high-sensitivity analysis of various therapeutic drugs in complex biological matrixes. In the preparation of PS-coated papers, the coating method was found playing a key role in determining the performance of the resulting paper substrate in addition to other parameters (e.g., starch type and amount, PS coating amount, and spray solvent). We also found that as a solvent was applied on PS-coated paper for paper spray, the analytes of interest would be first extracted out and then moved to the tip of paper triangle for spray along with the applied solvent. In the process, the surface energy of PS particles had a strong impact on the desorption performance of analytes from PS-coated paper substrate, and the PS with a high surface energy favored the elution of analytes to allow a high MS sensitivity. When the prepared PS coated paper was used as a substrate for paper spray, it gave high sensitivity in analysis of therapeutic drugs in various biological matrixes such as whole blood, serum, and urine with excellent repeatability and reproducibility. In contrast to uncoated filter paper, an improvement of 10-546-fold in sensitivity was achieved using PS-coated paper for paper spray, and an estimated lower limit of quantitation (LLOQs) in the range of 0.004-0.084 ng mL-1 was obtained. The present study is significant in exploring the potential of PS for high-sensitivity MS analysis, and it provides a promising platform in the translation of the MS technique to clinical applications.

Shape evolution of parallelogrammic magnesium oxalate controlled by phosphate species

Phosphate species are capable of playing a crucial role in manipulating the shapes and properties of inorganic materials. Herein, we examined the shape evolution of magnesium oxalate dihydrate (MgC2O4·2H2O) to parallelogrammic microparticles with sheet-like structure in a precipitation process under the influence of phosphate species in the form of sodium tripolyphosphate (Na5P3O10). Supported by a series of time-dependent experiments, the shape evolution of MgC2O4·2H2O was evidenced by the complexation and blocking effect of Na5P3O10 via a later adsorption at the surface of the formed MgC2O4·2H2O product. The results from scanning electron microscopy (SEM) images, energy dispersive spectroscopy (EDS) and X-ray photoelectron spectrometry (XPS) measurements show that the shape evolution of parallelogrammic particles is accompanied by a modification in the chemical composition via a later adsorption. Our results demonstrated that the amount of Na5P3O10 participating into the self-assembly of the layer-like parallelogram varied with reaction time. In the initial reaction stage, little amount of Na5P3O10 is involved in the particle formation, and the participating amount increased with extent of reaction. This investigation presents the effect of Na5P3O10 on the self-assembly of MgC2O4·2H2O particles with layer-like structure and highlights its role in the controllable synthesis of microparticles.