Jung-Lee Lin

MALDI Ion Trap Mass Spectrometer with Charge Detector for Large Biomolecule Detection

Up to now, all commercial matrix-assisted laser desorption/ionization (MALDI) mass spectrometers still can not efficiently analyze very large biomolecules. In this work, we report the development of a novel MALDI ion trap mass spectrometer which can enrich biomolecular ions to enhance the detection sensitivity. A charge detector was installed to measure the large ions directly. With this design, we report the first measurement of IgM with the mass-to-charge ratio (m/z) at 980 000. In addition, quantitative measurements of the number of ions can be obtained. A step function frequency scan was first developed to get a clear signal in the m/z range from 200,000 to 1,000,000.

High-Speed Mass Measurement of Nanoparticle and Virus

Until now, there have been no relatively easy methods to measure the mass and mass distributions of nanoparticles/viruses. In this work, we report the first set of measurements of mass and mass distributions for nanoparticles/viruses using a novel mass spectrometry technology. In the past, mass spectrometry was typically used to measure the mass of a particle or molecule with a mass less than 1,000,000 Da. We developed cell mass spectrometry that can measure the mass of a cell or a microparticle. Nevertheless, there is a gap for mass measurement methods in the mass region of a nanoparticle or virus (1 MDa to 1 GDa). Here, we developed a nanoparticle/virus mass spectrometry technique to make rapid and accurate mass and mass distribution measurements of nanoparticles/viruses. This technique should be valuable for the quality control of nanoparticle production and the identification of various viruses. In the future, this method can also serve to monitor drug delivery when nanoparticles are used as carriers. Furthermore, it may be possible to measure the degree of infection by measuring the number of viruses in specific cells or in plasma.

A numerical study on vibronic and vibrational dynamics generated by chirped laser pulses in the presence of relaxation processes

Abstract Detailed mechanisms of creation and destruction of coherence and population generated by the chirped pulses in the presence of the relaxation processes are numerically investigated. It is found that, during the intra-pulse pump–dump process of the negatively chirped pulse laser excitation, the vibronic coherence is sequentially created between the electronically excited and ground states. In this case, the pure dephasing process affects the time-ordered creation process of the population of each vibrational state in the electronically excited state.

A deeper look into sonic spray ionization

Sonic spray ionization (SSI) has been explored as an ambient ionization method for mass spectrometric analysis of different compounds. It has been applied to the analysis of different groups of compounds, mostly small molecules. The work reported in this paper extends the ionization efficiency of SSI and application of SSI to different groups of compounds, mostly biomolecules, in an ion trap mass spectrometer. SSI does not use any power supply and produces both positive and negative ions simultaneously. The most important parameters in SSI are gas pressure, solvent flow rate and physical dimensions of the spray device. Although the first two parameters have been investigated by different groups, the effect of physical dimensions has not been reported in the literature. Silica capillary inner diameter (ID) and outer diameter (OD) and ID of the cone play important roles in a spray. The best explored dimensions for the silica capillary are 150–200 μm OD and 40–75 μm ID and 350 μm ID for the cone. These physical dimensions provide the best ionization efficiency and spectra of large proteins such as albumin can be obtained. The spectra of the samples can also be collected in water without adding any acid into the solution.

Novel mass spectrometry technology development for large organic particle analysis

Recently, mass spectrometry has been extended to detect large organic particles and biomolecules, which include large protein polymers, organic polymers, nanoparticles, virions, microparticles and cells. Different novel technologies have been developed to detect these very large particles. In this review, a brief introduction to the technology development is given, and future perspectives on the applications are included. In terms of the detection of very large biomolecules, a macromolecular ion accelerator was developed to achieve sufficient molecular ion energy to reach the megavolt region and increase the detection efficiency. Ions with mass-to-charge ratios (m/z) reaching 30 000 000 were successfully detected. For larger organic or bioparticles, laser-induced acoustic desorption was developed for placing these particles inside a quadrupole ion trap. Measurements of the masses of mammalian and poultry erythrocytes, organic microparticles and cells were achieved by a mass spectrometer with laser-induced acoustic desorption, a frequency-scanning ion trap and charge detection. The mass distributions of these particles were also determined. For nanoparticles and viruses, the number of charges on each particle is too low for accurate determination by a charge detector. The direct detection of nanoparticles/virions by a charge amplification detector is not feasible due to the low velocities of these nanoparticles. A novel approach was developed based on the simultaneous measurement of the different sizes and different numbers of charges of each nanoparticle to derive the masses of the nanoparticles. Due to recent developments in the detection of large organic particles, mass spectrometry can be used to detect masses ranging from atoms to cells.

Triboelectric spray ionization

Triboelectric spray ionization (TESI) is a variation of electrospray ionization (ESI) using common instrumental components, including gas flow, solvent flow rate and heat, the only difference being the use of a high-voltage power supply for ESI or a static charge for TESI. The ionization of solvent or analyte is due to the electrostatic potential difference formed between the spray electrode and counter electrode. The ion source contains a pneumatic spray operated over a range of flow rates (0.15-1.5 µl/min) and gas pressures (0-100). This new design contains a standalone spray assembly and an optional metal mesh in front of the spray. There are several parameters that affect the performance during ionization of molecules including the flow rate of solvent, gas pressure, temperature, solvent acidity, distance and potential difference between emitter and counter electrode. A variable electrostatic potential can be applied for higher ionization efficiency. The new ionization method was successfully applied to solutions of various proteins under different conditions. The same charge-state distributions compared to other ESI techniques are observed for all the protein samples. The unique feature of TESI is very efficient spraying by using a natural electrostatic potential even at the potential that a human body can produce. This provides very gentle ionization efficiency of peptides and proteins in different solvents.

Biomolecular dual-ion-trap mass analyzer

We developed the first dual-ion-trap mass analyzer which can detect ions with a high mass-to-charge ratio (m/z > 6000). The first ion trap is a quadrupole ion trap (QIT), which was operated by step scanning of the trapping frequency for a sample containing mixtures of biomolecules. The second ion trap, linear ion trap (LIT), was utilized to capture selected ions ejected out of the QIT so that all ions from the QIT can be examined one by one. It was found that the ions can be transferred from the QIT to the LIT with ~60% efficiency for large biomolecular ions with high m/z. This is by far the highest transfer efficiency in the dual ion trap device for high-mass ions.

Macromolecular Ion Accelerator

Presented herein are the development of macromolecular ion accelerator (MIA) and the results obtained by MIA. This new instrument utilizes a consecutive series of planar electrodes for the purpose of facilitating stepwise acceleration. Matrix-assisted laser desorption/ionization (MALDI) is employed to generate singly charged macromolecular ions. A regular Z-gap microchannel plate (MCP) detector is mounted at the end of the accelerator to record the ion signals. In this work, we demonstrated the detection of ions with the mass-to-charge (m/z) ratio reaching 30,000,000. Moreover, we showed that singly charged biomolecular ions can be accelerated with the voltage approaching 1 MV, offering the evidence that macromolecular ions can possess much higher kinetic energy than ever before.

Novel Atmospheric Biomolecule Ionization Technologies

In general, atmospheric ionization is defined as an ionization process outside of the mass spectrometer vacuum chamber. During the past two decades, several novel atmospheric ionization methods were developed. Nevertheless, they can be divided into two major categories. One is direct analysis at real time (DART) and the other is modifications on electrospray ionization (ESI). In addition, some methods are used to analyze samples directly without any pretreatments. Those methods are often called as ambient ionization methods. Many atmospheric ionization methods are also considered as ambient ionizations. DART and desorption electrospray ionization are examples. Nevertheless, most atmospheric ionization methods involve the need of high voltage outside of the mass spectrometer vacuum chamber. In this review, we will only briefly introduce most of the existing methods which need high voltages. Most effort will be placed on the newly developed novel methods which do not need high voltages. They include Ultrasound Ionization (UI), Triboelectric Spray Ionization (TeSI) and Kelvin spray ionization (KeSI). These ionization methods don’t need to have any external high voltage power supply for ionization. They have the advantages of very soft ionization to keep bio molecular ions more similar to the structures in solution phase. Some related mechanisms will also be discussed.

ESI-MS measurements for the equilibrium constants of copper(II)-insulin complexes

Trace elements regulate many biological reactions in the body. Copper(II) is known as one of trace elements and capable of binding to proteins. Insulin is a blood glucose-lowering peptide hormone and it is secreted by the pancreatic β-cells. In this study, Cu(II)-insulin complexes were investigated by using ESI-MS method. Insulin molecule gives ESI-MS peaks at +4, +5, +6 and +7 charged states. Cu(II)-insulin complexes can be monitored and quantified on the ESI-MS spectra as the shifted peaks according to insulin peaks. The solutions of Cu(II)-insulin complexes at different pHs and mole ratios of Cu(II) ions to insulin molecule were measured on the ESI-MS. The highest complex formation ratio for Cu(II)-insulin were found at pH 7. The multiple bindings of Cu(II) ions to insulin molecule was observed. The formation equilibrium constants of Cu(II)-insulin complexes were calculated as Kf1: 3.34 × 104, Kf2: 2.99 × 104, Kf3: 7.00 × 103 and Kf4:2.86 × 103. The specific binding property of Cu(II) ions was controlled by using different spray ion sources including electrospray and nano-electrospray. The binding property of Cu(II) also investigated by MS/MS fragmentation. It was concluded from the ESI-MS measurements that Cu(II) ion has a high affinity to insulin molecules to form stable complexes.