Dual Enzymolysis Assisted by Acrylate or Phosphate Grafting: Influences on the Structural and Functional Properties of Jujube Residue Dietary Fiber.

Jujube residue is an abundant and low-cost dietary fiber resource, but its relatively lower hydration and functional properties limit its utilization as an ingredient of functional food. Thus, cellulase and hemicellulase hydrolysis, enzymatic hydrolysis assisted by phosphate grafting (EPG), and enzymatic hydrolysis assisted by acrylate grafting (EAG) were used to improve the functional properties of jujube residue dietary fiber (JRDF) in this study. The results evidenced that these modifications all increased the porosity of the microstructure of JRDF and increased the soluble fiber content, surface area, and hydration properties, but reduced its brightness (p < 0.05). Moreover, JRDF modified by enzymolysis combined with acrylate grafting offered the highest extractable polyphenol content, oil, sodium cholate, and nitrite ion sorption abilities. Meanwhile, JRDF modified via enzymolysis assisted by phosphate grafting showed the highest soluble fiber content (23.53 g∙100 g-1), water-retention ability (12.84 g∙g-1), viscosity (9.37 cP), water-swelling volume (10.80 mL∙g-1), and sorption ability of copper (II) and lead (II) ions. Alternatively, JRDF modified with cellulase hydrolysis alone exhibited the highest glucose adsorption capacity (21.9 g∙100 g-1) at pH 7.0. These results indicate that EPG is an effective way to improve the hypolipidemic effects of JRDF, while EAG is a good choice to enhance its hydration and hypoglycemic properties.

Paper-in-Tip Bipolar Electrospray Mass Spectrometry for Real-Time Chemical Reaction Monitoring.

Capturing short-lived intermediates at the molecular level is key to understanding the mechanism and dynamics of chemical reactions. Here, we have developed a paper-in-tip bipolar electrolytic electrospray mass spectrometry platform, in which a piece of triangular conductive paper incorporated into a plastic pipette tip serves not only as an electrospray emitter but also as a bipolar electrode (BPE), thus triggering both electrospray and electrolysis simultaneously upon application of a high voltage. The bipolar electrolysis induces a pair of redox reactions on both sides of BPE, enabling both electro-oxidation and electro-reduction processes regardless of the positive or negative ion mode, thus facilitating access to complementary structural information for mechanism elucidation. Our method enables real-time monitoring of transient intermediates (such as N,N-dimethylaniline radical cation, dopamine o-quinone (DAQ) and sulfenic acid with half-lives ranging from microseconds to minutes) and transient processes (such as DAQ cyclization with a rate constant of 0.15 s-1). This platform also provides key insights into electrocatalytic reactions such as Fe (III)-catalyzed dopamine oxidation to quinone species at physiological pH for neuromelanin formation.

On-Demand Portable Paper-Based Electrospray Ionization Mass Spectrometry for High-Sensitivity Analysis of Complex Samples.

Paper spray ionization has been demonstrated to be the most promising substrate-based source, but this technique suffers from the low desorption efficiency of target compounds and poor portability. In the current study, we describe a portable paper-based electrospray ionization (PPESI) in which a piece of triangle paper and adsorbent are packed sequentially into a modified disposable micropipette tip. This source not only captures the feature of paper spray and adsorbent for highly efficient suppression of sample matrixes for target compound analysis but also takes advantage of a micropipette tip to prevent spray solvent from rapid evaporation. The performance of developed PPESI depends on the type and amount of packed adsorbent, paper substrate, and spray solvent and applied voltage. Moreover, by contrast to other related sources, the analytical sensitivity and the spray duration of PPESI in tandem with MS have been improved by factors of 2.8-32.3 and 2.0-13.3, respectively. Based on its high accuracy (>96%) and precision (less than 3% relative standard deviation), the PPESI coupled to a mass spectrometer has been used to determine diverse therapeutic drugs and pesticides in complex biological (e.g., whole blood, serum, and urine) and food (e.g., milk and orange juice) matrixes, and the limits of detection and quantification were 2-4 pg mL-1 and 7-13 pg mL-1, respectively. Taking the portability, high sensitivity, and repeatability, the technique may be a promising alternative for complex sample analysis.

Improvement in the performance of focusing plasma desorption ionization by altering its counter electrode.

RATIONALE: Plasma-based ionization sources play a vital role in rapidly analyzing diverse compounds without extensive sample pretreatment. In contrast to other sources, DC voltage-based ionizations are more advantageous due to their high analytical sensitivity and good tandem with commercially available mass spectrometers without extra power supplies. However, their performance is at the risk of high current DC voltage and helium flow rate, which poses significant challenges to practical operation and increased expense. METHODS: In this work, we propose a novel focusing plasma desorption ionization (FPDI) in which a visible plasma beam is favorably generated between a conducting wire in a polymeric tube and a counter electrode composed of metal mesh and filter paper drilled with holes. A systematic investigation has been conducted on the influences of the geometry of drilled holes in filter paper, applied DC voltage, helium flow rate, and filter paper size. The optimized system is used to analyze various pesticides in fluid foodstuffs. RESULTS: Compared to metal mesh and conducting paper as the counter electrode for FPDI-MS, combining metal mesh and filter paper drilled holes improved the analysis sensitivity by a factor of more than five. By applying the developed protocol for determining pesticides in complex matrixes such as orange juice and milk, a limit of detection as low as 1.3-3.0 ng mL-1 could be achieved. CONCLUSIONS: A novel FPDI-MS technique has been developed by combining metal mesh and filter paper drilled with holes as the counter electrode and sample carrier. The corresponding improvement in analysis sensitivity facilitates the future expansion of FPDI-MS applications into different pesticides and other compounds in complex matrixes.

Nickel oxide morphology synthesized with a hydrothermal method for inverted perovskite solar cells.

In this paper, a hydrothermal method is used to synthesize a nickel oxide nanostructure (nano-NiO) for its application to inverted perovskite solar cells. These pore nanostructures were employed to increase both the contact and channel between the hole transport and perovskite layers of an ITO/nano-N i O/C H 3 N H 3 P b I 3/P C B M/A g device. The purpose of this research is twofold. First, three different nano-NiO morphologies were synthesized at temperatures of 140°C, 160°C, and 180°C. Then, a Raman spectrometer was used to check the phonon vibration and magnon scattering characteristics after an annealing temperature of 500°C. Second, nano-NiO powders were dispersed in isopropanol for subsequent spin coating on the inverted solar cells. The nano-NiO morphologies were multi-layer flakes, microspheres, and particles at synthesis temperatures of 140°C, 160°C, and 180°C, respectively. When the microsphere nano-NiO was used as the hole transport layer, the perovskite layer had a larger coverage of 83.9%. The grain size of the perovskite layer was analyzed by x-ray diffraction, and strong crystal orientations of (110) and (220) peaks were found. Despite this, the power conversion efficiency could affect the promotion, which is 1.37 times higher than the poly(3,4-ethylenedioxythiophene) polystyrene sulfonate element conversion efficiency of the planar structure.

Recent Advances in g-C3N4-Based Materials and Their Application in Energy and Environmental Sustainability.

Graphitic carbon nitride (g-C3N4), with facile synthesis, unique structure, high stability, and low cost, has been the hotspot in the field of photocatalysis. However, the photocatalytic performance of g-C3N4 is still unsatisfactory due to insufficient capture of visible light, low surface area, poor electronic conductivity, and fast recombination of photogenerated electron-hole pairs. Thus, different modification strategies have been developed to improve its performance. In this review, the properties and preparation methods of g-C3N4 are systematically introduced, and various modification approaches, including morphology control, elemental doping, heterojunction construction, and modification with nanomaterials, are discussed. Moreover, photocatalytic applications in energy and environmental sustainability are summarized, such as hydrogen generation, CO2 reduction, and degradation of contaminants in recent years. Finally, concluding remarks and perspectives on the challenges, and suggestions for exploiting g-C3N4-based photocatalysts are presented. This review will deepen the understanding of the state of the art of g-C3N4, including the fabrication, modification, and application in energy and environmental sustainability.

ACE-Inhibitory Peptides Identified from Quinoa Bran Glutelin-2 Hydrolysates: In Silico Screening and Characterization, Inhibition Mechanisms of ACE, Coordination with Zinc Ions, and Stability.

To obtain Angiotensin-I-Converting Enzyme (ACE) inhibition peptides with Zn-chelating capacity, quinoa bran glutelin-2 hydrolysates (QBGH) by Flavourzyme and Papain were subjected to Sephadex G-15 gel chromatography, reverse phase-high liquid performance chromatography and UPLC-ESI-MS/MS analysis. Four oligopeptides including GGGSGH, EAGAE, AGGGAGGG and AVPKPS were identified. Of these, only the hexapeptide AVPKPS had both ACE-inhibitory activity (IC50: 123.13 µmol/L) and Zn-chelating ability (17.36 mg/g). Molecular docking showed AVPKPS could bind with active residues Glu384 and Ala354 (both belong to the central S1 pocket of ACE including) through short hydrogen bond and hydrophobic interactions, respectively. Inhibition kinetics verified that AVPKPS was a competitive inhibitor of ACE. Moreover, AVPKPS can affect the zinc tetrahedral coordination in ACE through binding with residues His387 and His383. Fourier-transform infrared spectroscopy analysis demonstrated that the amino and carboxyl groups of AVPKPS were the main chelating sites for zinc ions. Under the gastrointestinal digestion, the ACE inhibition capacity of AVPKPS was relatively stable, and the zinc solubility of AVPKPS-zinc complexes was more stable than zinc sulfate (p < 0.05). These results suggest that quinoa peptides have potential applications as ingredients for antihypertension or zinc fortification.

Focusing Plasma Desorption/Ionization Mass Spectrometry.

A plasma-based source named focusing plasma desorption/ionization (FPDI) is described, which applies a high direct current voltage between a metal wire inside a polymeric hollow truncated cone and a piece of a one-sided coated conducting paper substrate. The conducting paper acts as both the counter electrode and the sample carrier. Upon the generation of a visible plasma beam, it would directly ionize the samples spotted on the conducting paper substrate or located around the plasma beam. The signal intensity of target analytes in mass spectrometric analysis is dependent highly on whether the conducting paper substrate is grounded or not, the type of conducting paper substrate, the inside diameter of the polymeric hollow truncated cone tip, the metal wire tip-to-polymer tip distance, the polymer tip-to-paper substrate distance, the applied voltage, and the helium flow rate. Based on the experimental observation, a plausible mechanism is proposed for the generation of the plasma beam from FPDI. Compared to the available low-temperature plasma, flowing atmospheric-pressure afterglow, and helium plasma ionization sources, FPDI has demonstrated higher sensitivity and better compatibility with commercial mass spectrometers without any extra power supplies. As a proof of concept, FPDI coupled with a mass spectrometer has also been applied for the discrimination of different brands of gasoline and determination of solid tablets and pesticides with limits of detection in the range of 2.2 to 30.7 ng mL-1.

Matrix-assisted nanoelectrospray mass spectrometry for soft ionization of metal(i)-protein complexes.

Metal ions play significant roles in biological processes, and investigation of metal-protein interactions provides a basis to understand the functions of metal ions in such systems. In the current study, a novel matrix-assisted nanoelectrospray ionization mass spectrometry (MANESI-MS) method was developed for investigating the interactions between metal ions (i.e., Cu+) and protein molecules (i.e., myoglobin) using Cu nanoparticles as the matrix. The results demonstrated that the present method not only was an efficient strategy for the generation of various complexes with monovalent metal ions, such as Cu+, in which no redox transitions between Cu+ and Cu2+ were observed, but also allowed a softer ionization of the generated Cu+-myoglobin complexes compared to that of myoglobin molecules with conventional nanoESI. Several parameters (i.e., the mixing mode of the myoglobin sample and Cu nanoparticle solution, size of the Cu particle, oxidation state of the Cu species, and acidity of the myoglobin solution) were found to be crucial in determining the ionization efficiency of the MANESI method. First loading a Cu nanoparticle solution into the electrospray tip followed by a myoglobin solution resulted in a favorable interaction between the generated Cu+ ions and myoglobin molecules, in which a smaller size of the Cu particle and a lower oxidation state of the metal species (Cu > Cu2O > CuO) gave a lower average charge state and hence a softer ionization of the resulting Cu+-myoglobin complexes, possibly due to the reduced denaturing effects of the Cu+ complex. The MANESI method has also been successfully used to ionize the complexes between Cu+ and other biological molecules such as cytochrome c and angiotension II, although an exception was found for lysozymes, which show an increase in the charge state. Analogous to the study with Cu, a variety of other metal nanoparticles (Ni, Fe, W, Ag, Al, Zn and Co) were explored to study their interactions with myoglobin, but only Zn and Co could produce monovalent metal ions (i.e., Zn+ and Co+) followed by a favorable interaction with myoglobin, and a soft ionization of the resulting complexes.

Correction: Metal salt assisted electrospray ionization mass spectrometry for the soft ionization of GAP polymers in negative ion mode.

Correction for 'Metal salt assisted electrospray ionization mass spectrometry for the soft ionization of GAP polymers in negative ion mode' by Theoneste Muyizere et al., Analyst, 2020, 145, 34-45.

Metal salt assisted electrospray ionization mass spectrometry for the soft ionization of GAP polymers in negative ion mode.

Glycidyl azide polymers (GAP) are one of the most important energetic polymers, but it is still a challenge to elucidate their structures using mass spectrometry due to their fragility upon ionization. Herein we developed a soft metal salt assisted electrospray ionization (MSAESI) to characterize directly GAP polymers using mass spectrometry. This technique combines paper spray ionization and the complexing effect of anions from metal salts with GAP in the negative ion mode to softly ionize GAP polymers prior to mass spectrometry analysis. The effects of experimental parameters (e.g., ion mode, applied voltage, and type and concentration of metal salts) have been investigated in detail. In contrast to the positive ion mode, a softer ionization was observed for GAP polymers when the negative ion mode was applied. The radius and average charge of cations and anions in metal salts were found to play crucial roles in determining the performance of the MSAESI analysis of GAP. For a given charge number, a smaller radius of cations favored the soft ionization of GAP polymers (e.g., Na+ > K+ > Rb+), whereas a larger radius of anions led to a preferred performance (e.g., F- < Cl- < Br- < I-) due to variation in dissolution ability. For anions with multiple charges, the ones with fewer charges gave a more favorable ionization to the GAP sample because of their better complexing to GAP molecules than those with more charges in the structure of anions (e.g., NO3- > SO42- > PO43-). According to the experimental observation and evidence from mass spectrometry, we proposed the plausible electrospray mechanisms of MSAESI for GAP analysis with the involvement of metal salts. Moreover, the developed protocol has been applied successfully to the analysis of various GAP samples, and works for other types of sources such as nanoelectrospray ionization.

Discovery of Potent Inhibitors of 11ß-Hydroxysteroid Dehydrogenase Type 1 Using a Novel Growth-Based Protocol of in Silico Screening and Optimization in CONTOUR.

With the continuous progress in ultralarge virtual libraries which are readily accessible, it is of great interest to explore this large chemical space for hit identification and lead optimization using reliable structure-based approaches. In this work, a novel growth-based screening protocol has been designed and implemented in the structure-based design platform CONTOUR. The protocol was used to screen the ZINC database in silico and optimize hits to discover 11ß-HSD1 inhibitors. In contrast to molecular docking, the virtual screening process makes significant improvements in computational efficiency without losing chemical equities through partitioning 1.8 million ZINC compounds into fragments, docking fragments to form key hydrogen bonds with anchor residues, reorganizing molecules into molecular fragment trees using matched fragments and common substructures, and then regrowing molecules with the help of developed intelligent growth features inside the protein binding site to find hits. The growth-base screening approach is validated by the high hit rate. A total of 50 compounds have been selected for testing; of these, 15 hits having diverse scaffolds are found to inhibit 11ß-HSD1 with IC50 values of less than 1 µM in a biochemical enzyme assay. The best hit which exhibits an enzyme IC50 of 33 nM is further developed to a novel series of bicyclic 11ß-HSD1 inhibitors with the best inhibition of enzyme IC50 of 3.1 nM. The final lead candidate exhibits IC50 values of 7.2 and 21 nM in enzyme and adipocyte assays, respectively, displayed greater than 1000-fold of selectivity over 11ß-HSD2 and two other related hydroxysteroid dehydrogenases, and can serve as good starting points for further optimization to develop clinical candidates.

Isolation of Novel ACE-Inhibitory and Antioxidant Peptides from Quinoa Bran Albumin Assisted with an In Silico Approach: Characterization, In Vivo Antihypertension, and Molecular Docking.

Albumin is the major fraction of quinoa protein that is characterized as having high nutritional value. However, until now, scant information is available on the bioactivity of quinoa albumin or its hydrolysates. To promote its usage, we extracted albumin in this study from quinoa bran assisted with cellulase and hemicellulose, and hydrolyzed it by alcalase and trypsin to produce bioactive peptides. The hydrolysates (QBAH) were purified by gel filtration and reversed-phase high-performance liquid chromatography (RP-HPLC), followed by identification using liquid chromatography-mass spectrometry (LC-MS/MS). Furthermore, based on in silico analysis, one angiotensin-I converting enzyme (ACE)-inhibitory and antioxidant peptide, RGQVIYVL (946.6 Da), and two antioxidant peptides, ASPKPSSA (743.8 Da), and QFLLAGR (803.5 Da), from QBAH were synthesized. RGQVIYVL showed a high ACE-inhibitory activity (IC50 = 38.16 µM) with competitive mode of inhibition, and showed significant antihypertensive effect in spontaneously hypertensive rats at a concentration of 100-150 mg/kg body weight (bw). Molecular docking simulation showed that it could interact with the active ACE site via hydrogen bonds with high binding power. Moreover, RGQVIYVL, ASPKPSSA, and QFLLAGR all demonstrated high ·OH scavenging activity (IC50 = 61.69-117.46 µM), ABTS+ scavenging activity (58.29-74.28%) and Fe2+ chelating ability (32.54-82.48% at 0.5 mg/mL). They could also retain activity after gastrointestinal enzyme digestion. These results indicate that quinoa albumin is a potential source of bioactive peptides possessing antioxidant and ACE-inhibitory activities.

Elucidating the Reaction Mechanisms between Triazine and Hydrogen Sulfide with pH Variation Using Mass Spectrometry.

Triazine is one of the most economical and effective scavengers for hydrogen sulfide (H2S) removal, but the reaction mechanisms between triazine and H2S with pH variation in solution are still poorly understood. Herein, we show that the reaction process can be directly probed by means of paper spray mass spectrometry, in which an aprotic solvent (e.g., acetonitrile) is more favorable to the observation of reaction intermediates than a protic solvent (e.g., methanol), because of hydrogen bond interaction. Varying the pH of the reaction leads to completely different reaction pathways. With the pH in the range of 5.58 to 7.73, the major product was thiadiazine. With a pH of 3.02-3.69, thiadiazine is converted to 2-(5-(2-hydroxyethyl)-1,3,5-thiadiazinan-3-yl)acetaldehyde, which differs from the traditional pathway of analogous reactions. However, as ammonia was added into the reaction and the pH was adjusted to the range 8.45-9.43, triazine readily undergoes hydrolysis, and the formed intermediate reacts with ammonia and formaldehyde generated in situ from triazine to produce 1-(2-hydroxyethyl)-3,5,7-triaza-1-azoniatricyclo [3.3.1.13,7]decane (HTAD). Further increasing the pH up to 10.27-11.21 leads to the decomposition of HTAD. Based on the experimental observation and evidence from high-resolution and tandem mass spectrometry, we propose the plausible reaction mechanisms between triazine and H2S, as well as the derived reaction from triazine under different pH conditions.

Double resonance ejection using novel radiofrequency phase tracking circuitry in a miniaturized planar linear ion trap mass spectrometer.

RATIONALE: Ion trap mass spectrometers are attractive due to their inherent sensitivity and specificity. Miniaturization increases trap portability for in situ mass analysis by relaxing vacuum and voltage requirements but decreases the trapping volume. To overcome signal/resolution loss from miniaturization, double resonance ejection using phase tracking circuitry was investigated. METHODS: Phase tracking circuitry was developed to induce double resonance ejection in a planar linear ion trap using the ß 2/3 hexapole resonance line. RESULTS: Double resonance was observed using phase tracking circuitry. Resolution of 0.5 m/z units and improved signal-to-noise ratio (SNR) compared with AC resonant ejection were achieved. CONCLUSIONS: The phase tracking circuitry proved effective despite deviations from a true phase locked condition. Double resonance ejection is a means to increase signal intensity in a miniaturized planar ion trap.

Antioxidant Activity of Coconut (Cocos nucifera L.) Protein Fractions.

Coconut cake is an abundant and good potential edible protein source. However, until now it has not been extensively used in the food industry. To promote its usage, the characterization, nutrition value and antioxidant activity of coconut cake protein fractions (albumin, globulin, prolamine, glutelin-1 and glutelin-2) were studied. Results revealed that all the albumin, globulin, glutelin-1 and glutelin-2 fractions showed a high nutrition value. The prolamine, glutelin-1 and glutelin-2 all exhibited good radical scavenging activity and reducing power, and the globulin and prolamine showed high ion chelating ability (89.14-80.38%). Moreover, all the fractions except glutelin-2 could effectively protect DNA against oxidative damage. Several peptides containing five to eight amino acids with antioxidant activity were also identified by LC-MS/MS from the globulin and glutelin-2 fractions. The results demonstrated that the coconut cake protein fractions have potential usages in functional foods.

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.

Conformational control in structure-based drug design.

In structure-based drug design, the basic goal is to design molecules that fit complementarily to a given binding pocket. Since such computationally modeled molecules may not adopt the intended bound conformation outside the binding pocket, one challenge is to ensure that the designed ligands adopt similar low energy conformations both inside and outside of the binding pocket. Computational chemistry methods and conformational preferences of small molecules from PDB and Cambridge Structural Database (CSD) can be used to predict the bound structures of the designed molecules. Herein, we review applications of conformational control in structure-based drug design using selected examples from the recent medicinal chemistry literature. The main purpose is to highlight some intriguing conformational features that can be applied to other drug discovery programs.

Development and Application of Zirconia Coated Paper Substrate for High Sensitivity Analysis of Therapeutic Drugs in Dried Blood Spots.

Paper spray mass spectrometry has been demonstrated to be promising for direct analysis of therapeutic drugs in dried blood spots (DBS); however, the strong hydrogen bond and van de Waals interactions between paper substrate and analytes containing polar functional groups (e.g., therapeutic drugs) affect greatly the elution behavior and analysis sensitivity of compounds of interest during paper spray. Herein, we developed a one-sided ZrO2 coated paper substrate through a facile vacuum filtration approach using commercial ZrO2 particles as coating material and soluble starch as adhesive agent. Owing to the unique surface properties, as-prepared ZrO2 paper substrate has been shown to have excellent performance for analysis of therapeutic drugs in DBS during paper spray mass spectrometry. In contrast to original cellulose paper substrates, improvements of 43-189-fold in lower limit of quantitation (LLOQ) were obtained for the tested drugs using ZrO2 coated paper for paper spray. In comparing with the previously reported grade SG81 paper and one-sided silica coated paper, the LLOQs of the tested drugs with as-prepared ZrO2 paper decreased 1.5-16.5-fold relative to those from the above two, revealing that ZrO2 coated paper is a good candidate for paper spray in high sensitivity analysis of therapeutic drugs in DBS.

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 © 2016 John Wiley & Sons, Ltd.