Lingpeng Zhan

Quantitative Assessment of Protein Adsorption on Microparticles with Particle Mass Spectrometry

In this paper, particle mass spectrometry (PMS), which consists of an aerodynamic desorption/ionization (AD) source, a quadrupole ion trap (QIT) mass analyzer, and a charge detector, was exploited to characterize the protein adsorption on microparticles based on the mass variations of microparticles before and after protein adsorption. This method is simple and has low sample cost. Importantly, its mass resolution is good enough to distinguish the microparticles with and without protein. For the adsorption of bovine serum albumin (BSA) on 3 μm porous poly styrene-divinylbenzene (poly S-DVB), the minimum mass increase that can be resolved by PMS corresponds to 128 fg (1.8 ng/cm(2)) or 1.17 × 10(6) BSA molecules on each poly S-DVB particle. With PMS, the adsorption process of BSA on poly S-DVB spheres was successfully characterized, and the obtained maximum adsorption capacity qm and dissociation constant Kd were consistent with that determined by the conventional depletion method. In addition, the influence of surface modification of silica particles on the enzyme immobilization was evaluated. Compared with C4 (propyldimethylsilane), C8 (octyldimethylsilane), and Ph (phenyldimethylchlorosilane), the CN (cyanoethyldimethylchlorosilane) functionalized silica particles were screened to be most beneficial for the immobilization of both lysozyme and trypsin.

A Theoretical Method for Characterizing Nonlinear Effects in Paul Traps with Added Octopole Field

AbstractIn comparison with numerical methods, theoretical characterizations of ion motion in the nonlinear Paul traps always suffer from low accuracy and little applicability. To overcome the difficulties, the theoretical harmonic balance (HB) method was developed, and was validated by the numerical fourth-order Runge-Kutta (4th RK) method. Using the HB method, analytical ion trajectory and ion motion frequency in the superimposed octopole field, ε, were obtained by solving the nonlinear Mathieu equation (NME). The obtained accuracy of the HB method was comparable with that of the 4th RK method at the Mathieu parameter, q = 0.6, and the applicable q values could be extended to the entire first stability region with satisfactory accuracy. Two sorts of nonlinear effects of ion motion were studied, including ion frequency shift, Δβ, and ion amplitude variation, Δ(C2n/C0) (n ≠ 0). New phenomena regarding Δβ were observed, although extensive studies have been performed based on the pseudo-potential well (PW) model. For instance, the |Δβ| at ε = 0.1 and ε = –0.1 were found to be different, but they were the same in the PW model. This is the first time the nonlinear effects regarding Δ(C2n/C0) (n ≠ 0) are studied, and the associated study has been a challenge for both theoretical and numerical methods. The nonlinear effects of Δ(C2n/C0) (n ≠ 0) and Δβ were found to share some similarities at q < 0.6: both of them were proportional to ε, and the square of the initial ion displacement, z(0)2. Graphical Abstractᅟ

Nonlinear Effects in Paul Traps Operated in the Second Stability Region: Analytical Analysis and Numerical Verification

AbstractPaul trap working in the second stability region has long been recognized as a possible approach for achieving high-resolution mass spectrometry (MS), which however is still far away from the experimental implementations because of the narrow working area and inefficient ion trapping. Full understanding of the ion motional behavior is helpful for solving the problem. In this article, the ion motion in a superimposed octopole field, which was characterized by the nonlinear Mathieu equation, was solved analytically using Poincare-Lighthill-Kuo (PLK) method. This method equivalently described the nonlinear disturbance by an effective quadrupole field with perturbed Mathieu parameters, au′ and qu′, which would bring huge convenience in the studies of nonlinear ion dynamics and was, therefore, used for rapid evaluation of the nonlinear effects of ion motion. Fourth-order Runge-Kutta method (4th R-K) indicated the error of PLK for characterizing the frequency shift of ion motion was within 15%. Figureᅟ

Investigation and Applications of In-Source Oxidation in Liquid Sampling-Atmospheric Pressure Afterglow Microplasma Ionization (LS-APAG) Source

AbstractA liquid sampling-atmospheric pressure afterglow microplasma ionization (LS-APAG) source is presented for the first time, which is embedded with both electrospray ionization (ESI) and atmospheric pressure afterglow microplasma ionization (APAG) techniques. This ion source is capable of analyzing compounds with diverse molecule weights and polarities. An unseparated mixture sample was detected as a proof-of-concept, giving complementary information (both polarities and non-polarities) with the two ionization modes. It should also be noted that molecular mass can be quickly identified by ESI with clean and simple spectra, while the structure can be directly studied using APAG with in-source oxidation. The ionization/oxidation mechanism and applications of the LS-APAG source have been further explored in the analysis of nonpolar alkanes and unsaturated fatty acids/esters. A unique [M + O – 3H]+ was observed in the case of individual alkanes (C5–C19) and complex hydrocarbons mixture under optimized conditions. Moreover, branched alkanes generated significant in-source fragments, which could be further applied to the discrimination of isomeric alkanes. The technique also facilitates facile determination of double bond positions in unsaturated fatty acids/esters due to diagnostic fragments (the acid/ester-containing aldehyde and acid oxidation products) generated by on-line ozonolysis in APAG mode. Finally, some examples of in situ APAG analysis by gas sampling and surface sampling were given as well. Graphical Abstractᅟ

Nonlinear Ion Harmonics in the Paul Trap with Added Octopole Field: Theoretical Characterization and New Insight into Nonlinear Resonance Effect

AbstractThe nonlinear harmonics within the ion motion are the fingerprint of the nonlinear fields. They are exclusively introduced by these nonlinear fields and are responsible to some specific nonlinear effects such as nonlinear resonance effect. In this article, the ion motion in the quadrupole field with a weak superimposed octopole component, described by the nonlinear Mathieu equation (NME), was studied by using the analytical harmonic balance (HB) method. Good accuracy of the HB method, which was comparable with that of the numerical fourth-order Runge-Kutta (4th RK), was achieved in the entire first stability region, except for the points at the stability boundary (i.e., β = 1) and at the nonlinear resonance condition (i.e., β = 0.5). Using the HB method, the nonlinear 3β harmonic series introduced by the octopole component and the resultant nonlinear resonance effect were characterized. At nonlinear resonance, obvious resonant peaks were observed in the nonlinear 3β series of ion motion, but were not found in the natural harmonics. In addition, both resonant excitation and absorption peaks could be observed, simultaneously. These are two unique features of the nonlinear resonance, distinguishing it from the normal resonance. Finally, an approximation equation was given to describe the corresponding working parameter, qnr, at nonlinear resonance. This equation can help avoid the sensitivity degradation due to the operation of ion traps at the nonlinear resonance condition. Graphical Abstractᅟ

Differentiation and Relative Quantitation of Disaccharide Iso-mers by MALDI-TOF/TOF Mass Spectrometry

Saccharide isomer differentiation has been a challenge in glycomics, as the lack of technology to decipher fully the diverse structures of compositions, linkages, and anomeric configurations. Several mass spectrometry-based methods have been applied to the discrimination of disaccharide isomers, but limited quantitative analyses have been reported. In the present study, MALDI-LIFT-TOF/TOF has been investigated to differentiate and relatively quantify underivatized glucose-containing disaccharide isomers that differ in composition, connectivity or configuration. N-(1-naphthyl)ethylenediamine dihydrochloride (NEDC) was used as a highly sensitive matrix without matrix interferences in low mass range, thus yielding intense chloride-attached disaccharide ions [M + Cl]-, which could be fragmented to give diagnostic characteristic fragment patterns for distinguishing these isomers. Three different types of disaccharide isomers were successfully relatively quantified in a binary mixture using the specific product ion pairs. Finally, this method was utilized to identify and relatively quantify two disaccharide isomers in Medicago leaf (maltose and sucrose) without numerous preparation steps. In general, this method is a fast, effective, and robust method for rapid differentiation and quantitation of disaccharide isomers in complex medium.

The bridge between thin layer chromatography-mass spectrometry and high-performance liquid chromatography-mass spectrometry: The realization of liquid thin layer chromatography-mass spectrometry ☆

The combination of thin layer chromatography (TLC) and mass spectrometry (MS) has been studied for decades, but for most cases MS detection is done after TLC separation is finished. Here, an online simultaneous TLC-MS analysis system, liquid thin layer chromatography-mass spectrometry (LTLC-MS), is developed which successfully synchronize TLC separation process and MS detection process like GC-MS and HPLC-MS do. And theres no need to use specially designed TLC, just regular TLC plates are enough. LTLC-MS method is composed of a newly developed ambient ionization method, glow discharge-matrix assisted infrared desorption ionization (GD-MAIRDI), and forced-flow TLC (FFTLC) technique, which guarantees the MS detection process does not disturb the TLC separation process throughout the whole analysis. The whole LTLC-MS analysis only need two steps and less than 15min. Mixtures as well as the two main components of a pain relief pills have been successfully analyzed by LTLC-MS. This proof of concept study opens up new possibilities of combining TLC with MS, and will further broaden the application abilities of TLC.

Utilizing A Mini-humidifier To Deposit Matrix For MALDI-Imaging

MALDI mass spectrometry imaging (MALDI-MSI) is a powerful tool to study endogenous metabolites. The process of matrix deposition is crucial for a high-quality imaging result. Commercial instruments for matrix deposition are expensive. Low-cost methods like airbrushing will generate matrix crystals that are too large for high-spatial-resolution imaging. Sublimation may cause some compounds to go undetected because of the lack of solvent. Herein, we utilized a mini-humidifier, costing less than 5 dollars, to deposit matrix for MALDI-MSI. Compared with Imageprep, a commercialized instrument, our device based on the humidifier provided higher sensitivity and much smaller matrix crystals with diameters of less than 10 μm. High-quality ion images with 10 μm spatial resolution were obtained using our method. The enhancement of sensitivity by the humidifier could provide a sufficient amount of ions to perform tandem mass imaging. We also performed MALDI-MS/MS imaging to separate two lipids in mouse brain.

N-Phenyl-2-naphthylamine as a Novel MALDI Matrix for Analysis and in Situ Imaging of Small Molecules

Due to its strong ultraviolet absorption, low background interference in the small molecular range, and salt tolerance capacity, N-phenyl-2-naphthylamine (PNA) was developed as a novel matrix in the present study for analysis and imaging of small molecules by matrix-assisted laser desorption/ionization mass spectrometry time-of-fight (MALDI-TOF MS). The newly developed matrix displayed good performance in analysis of a wide range of small-molecule metabolites including free fatty acids, amino acids, peptides, antioxidants, and phospholipids. In addition, PNA-assisted LDI MS imaging of small molecules in brain tissue of rats subjected to middle cerebral artery occlusion (MCAO) revealed unique distributions and changes of 89 small-molecule metabolites including amino acids, antioxidants, free fatty acids, phospholipids, and sphingolipids in brain tissue 24 h postsurgery. Fifty-nine of the altered metabolites were identified, and all the changed metabolites were subject to relative quantitation and statistical analysis. The newly developed matrix has great potential application in the field of biomedical research.

Heat-Induced Rearrangement of the Disulfide Bond of Lactoglobulin Characterized by Multiply Charged MALDI-TOF/TOF Mass Spectrometry

Disulfide bonds are an important post-translational modification of proteins and play a significant role in stabilizing protein structure. While both mass spectrometry-based bottom-up and top-down proteomics are widely used in the identification of disulfide linkages, the top-down approach can avoid potential information loss of disulfide linkage occurring in the bottom-up analysis. In the present work, we applied matrix-assisted laser desorption/ionization tandem Time-of-Flight (MALDI-TOF/TOF) mass spectrometry to investigate the heat-induced disulfide rearrangement of β-lactoglobulin (β-LG). Since β-LG (18 kDa) is too large for common TOF/TOF analysis, we use 2-nitrophloroglucinol (2-NPG) as a matrix to generate multiply charged proteins by MALDI. Fragmentation of doubly charged protein ions yields characteristic triplet peaks of disulfide bonds. We found that the characteristic fragments derived from the heterolytic cleavage of disulfide bonds decreased sharply when the incubation temperature of β-LG solution reached the critical point of 75 °C. These results indicate that the disulfide linkage between C160 and C66 has been broken during the heating process and, probably, new disulfide formed. In conclusion, our work highlights the analytical value of the multiply charged MALDI-TOF/TOF method in the identification of larger proteins (>12 kDa) and disulfide-containing proteins.