Jentaie Shiea

Ambient Ionization Mass Spectrometry

Mass spectrometric ionization methods that operate under ambient conditions and require minimal or no sample pretreatment have attracted much attention in such fields as biomedicine, food safety, antiterrorism, pharmaceuticals, and environmental pollution. These technologies usually involve separate ionization and sample-introduction events, allowing independent control over each set of conditions. Ionization is typically performed under ambient conditions through use of existing electrospray ionization (ESI) or atmospheric pressure chemical ionization (APCI) techniques. Rapid analyses of gas, liquid, and solid samples are possible with the adoption of various sample-introduction methods. This review sorts different ambient ionization techniques into two main subcategories, primarily on the basis of the ionization processes, that are further differentiated in terms of the approach used for sampling.

Ambient ionization mass spectrometry: a tutorial.

Ambient ionization is a set of mass spectrometric ionization techniques performed under ambient conditions that allows the direct analysis of sample surfaces with little or no sample pretreatment. Using combinations of different types of sample introduction systems and ionization methods, several novel techniques have been developed over the last few years with many applications (e.g., food safety screening; detection of pharmaceuticals and drug abuse; monitoring of environmental pollutants; detection of explosives for antiterrorism and forensics; characterization of biological compounds for proteomics and metabolomics; molecular imaging analysis; and monitoring chemical and biochemical reactions). Electrospray ionization and atmospheric pressure chemical ionization are the two main ionization principles most commonly used in ambient ionization mass spectrometry. This tutorial paper provides a review of the publications related to ambient ionization techniques. We describe and compare the underlying principles of operation, ionization processes, detecting mass ranges, sensitivity, and representative applications of these techniques.

Thin layer chromatography/mass spectrometry.

Thin layer chromatography (TLC)--a simple, cost-effective, and easy-to-operate planar chromatographic technique--has been used in general chemistry laboratories for several decades to routinely separate chemical and biochemical compounds. Traditionally, chemical and optical methods are employed to visualize the analyte spots on the TLC plate. Because direct identification and structural characterization of the analytes on the TLC plate through these methods are not possible, there has been long-held interest in the development of interfaces that allow TLC to be combined with mass spectrometry (MS)--one of the most efficient analytical tools for structural elucidation. So far, many different TLC-MS techniques have been reported in the literature; some are commercially available. According to differences in their operational processes, the existing TLC-MS systems can be classified into two categories: (i) indirect mass spectrometric analyses, performed by scraping, extracting, purifying, and concentrating the analyte from the TLC plate and then directing it into the mass spectrometers ion source for further analysis; (ii) direct mass spectrometric analyses, where the analyte on the TLC plate is characterized directly through mass spectrometry without the need for scraping, extraction, or concentration processes. Conventionally, direct TLC-MS analysis is performed under vacuum, but the development of ambient mass spectrometry has allowed analytes on TLC plates to be characterized under atmospheric pressure. Thus, TLC-MS techniques can also be classified into two other categories according to the working environment of the ion source: vacuum-based TLC-MS or ambient TLC-MS. This review article describes the state of the art of TLC-MS techniques used for indirect and direct characterization of analytes on the surfaces of TLC plates.

Electrospray-Assisted Laser Desorption/Ionization Mass Spectrometry for Continuously Monitoring the States of Ongoing Chemical Reactions in Organic or Aqueous Solution under Ambient Conditions

Electrospray-assisted laser desorption/ionization (ELDI) combined with mass spectrometry allows chemical and biochemical compounds to be characterized directly from hydrophilic and hydrophobic organic solutions mixed with carbon powders under ambient conditions. Organic and inorganic compounds dissolved in polar or nonpolar solvent such as methanol, tetrahydrofuran, ethyl acetate, toluene, dichloromethane, or hexane can be detected using this ambient ionization technique without prior pretreatment. We have used this technique to monitor the progress in several ongoing reactions: the epoxidation of chalcone in ethanol, the chelation of ethylenediaminetetraacetic acid with copper and nickel ions in aqueous solution, the chelation of 1,10-phenanthroline with iron(II) in methanol, and the tryptic digestion of cytochrome c in aqueous solution. Liquid-ELDI analyses simply require irradiation of the surface of the sample solution with a pulsed ultraviolet laser; the laser energy is adsorbed by the carbon powder presuspended in the sample solution; the absorbed laser energy is then transferred to the surrounding solvent and to the analyte molecules in the solution, leading to their desorption; the desorbed gaseous analyte molecules are then postionized within an electrospray (ESI) plume to generate ESI-like analyte ions.

Skp2 overexpression increases the expression of MMP-2 and MMP-9 and invasion of lung cancer cells.

Skp2 is one of the components of the E3 ubiquitin ligase which is required for the degradation of tumor suppressor p27. Overexpression of this oncogene is frequently found in human cancers and has been shown to be associated with poor prognosis. In addition to induce p27 degradation and enhance cellular proliferation, Skp2 also plays a role in promoting tumor metastasis. However, the underlying mechanism is unclear. In this study, we established Skp2-overexpressing stable transfectants from A549 human lung cancer cells. We found that these stable transfectants exhibited increased migratory and invasive abilities. In addition, expression of matrix metalloproteinase-2 (MMP-2) and MMP-9 was up-regulated. Enzymatic assay and gelatin zymography confirmed the increase of MMP-2 and MMP-9 activity and neutralization of these two MMPs by antibodies reduced cell invasion. Our results also revealed that Sp1 was involved in the induction of MMP-2 and MMP-9 by Skp2 because treatment of mithramycin or knockdown of Sp1 by small interference RNA attenuated their expressions. Collectively, we provide the first evidence that up-regulation of MMP-2 and MMP-9 is one of the mechanisms by which Skp2 promotes cell invasion.

Application of direct electrospray probe to analyze biological compounds and to couple to solid-phase microextraction to detect trace surfactants in aqueous solution

This work presents two novel direct electrospray probes (DEP) to generate an electrospray without using a capillary and/or syringe pump. One of the DEPs is simply a copper coil connecting to a high-voltage power supply. The sample solution is deposited on the coil by a micropipet and the electrospray is subsequently generated at the tip of the copper coil after high voltage is applied to it. Another DEP is constructed by inserting two parallel optical fibers through the copper coil. The two fibers extend one end of the copper coil by 1 cm. Electrospray is generated at the tip of the fibers through the solution predeposited on the copper coil as the high voltage is applied on the copper coil. The ES mass spectra of myoglobin in liquid or solid phases can be obtained using this DEP-MS. Coupling the DEP to a solid-phase microextraction fiber is extremely easy, and a trace amount (in ppb range) of surfactants (Triton X-100) in the aqueous solution are selectively concentrated and detected.

Using laser-induced acoustic desorption/electrospray ionization mass spectrometry to characterize small organic and large biological compounds in the solid state and in solution under ambient conditions.

We have coupled laser-induced acoustic desorption (LIAD) with electrospray ionization (ESI) mass spectrometry (LIAD/ESI/MS) to characterize molecules in the solid state and in solution under ambient conditions. To perform an LIAD/ESI analysis, the sample droplet is deposited on the surface of a thin aluminum foil by a micropipette; the rear side of the foil with the sample spot is then irradiated with a pulse from a Nd:YAG IR laser. The resulting shockwave and heat cause the sample on the rear side to change from the condensed phase to the gas phase. The desorbed species then move upward to enter an ESI plume to react with charged solvent species (methanol- and water-related ions and droplets), forming singly or multiply charged analyte ions. A quadrupole/time-of-flight (Q-TOF) mass analyzer attached to the LIAD/ESI source detects the analyte ions to obtain an ESI-like mass spectrum. Both small organic and large biological compounds (including amino acids, peptides, and proteins) were successfully ionized and detected by the LIAD/ESI/MS system. Although native and denatured myoglobin ions were both detected from a liquid sample solution, only the denatured myoglobin ions were detected from a dried sample.

Detection of Native Protein Ions in Aqueous Solution under Ambient Conditions by Electrospray Laser Desorption/Ionization Mass Spectrometry

Liquid electrospray laser desorption/ionization (ELDI) mass spectrometry allows desorption and ionization of proteins directly from aqueous solutions and biological fluids under ambient conditions. Native protein ions such as those of myoglobin, cytochrome c, and hemoglobin were obtained. A droplet (ca. 5 microL) containing the protein molecules and micrometer-sized particles (e.g., carbon graphite powder) is irradiated with a pulsed UV laser. The laser energy adsorbed by the inert particles is transferred to the surrounding solvent and protein molecules, leading to their desorption; the desorbed gaseous molecules are then postionized within an electrospray (ESI) plume to generate the ESI-like protein ions. With the use of this technique, we detected only the protonated protein ions in various biological fluids (including human tears, cow milk, serum, and bacterial extracts) without interference from their corresponding sodiated or potassiated adduct ions. In addition, we rapidly quantified the levels of glycosylated hemoglobin present in drops of whole blood obtained from diabetic patients without the need of sample pretreatment.

GENERATING ELECTROSPRAY FROM SOLUTIONS PREDEPOSITED ON A COPPER WIRE

This study presents a novel direct probe (DP) to perform electrospray ionization (ESI). The probe is constructed simply from a thin copper ring connected to a high voltage power supply, and a capillary and syringe pump are unnecessary. Approximately one microliter of the sample solution is applied directly onto the copper ring by a micropipette. Electrospray from the solution on the copper ring is induced by surface deformation by deflecting a droplet from the copper ring. The mass spectra of proteins obtained by DP–ESI are exactly the same as those from conventional ESI sources through a capillary needle. The time deemed necessary to complete an analysis is approximately 2 minutes, and sample switching is immediate. The signals of the analyte can last from 45 seconds to more than 10 minutes depending on probe design. Three different types of probes used to retain more sample solution on the probe during electrospray were designed and constructed. Moreover, cleaning the probe between different sample analysis is easy. Since a capillary is not used for sample transportation, presence of the particles in the sample solution does not interfere with the electrospray process by capillary blockage. Copyright

Thin-Layer Chromatography/Laser-Induced Acoustic Desorption/Electrospray Ionization Mass Spectrometry

The combination of laser-induced acoustic desorption and electrospray ionization mass spectrometry (LIAD/ESI/MS) can be used to rapidly characterize chemical compounds separated on a thin layer chromatography (TLC) plate. We performed LIAD analysis by irradiating the rear side of an aluminum-based TLC plate with a pulsed infrared (IR) laser. To efficiently generate and transfer acoustic and shock waves to ablate the analyte-containing TLC gels, a glass slide was attached to the rear of the TLC plate and the gap between the glass slide and the TLC plate was filled with a viscous solution (glycerol). Although the diameter of the laser spot created on the rear of the TLC plate was approximately 0.35 mm, the ablated areas on the front sides of the silica gel bed and the C(18) reverse-phase gel bed had diameters of approximately 1.3 and 3 mm, respectively. The ablated analyte molecules were ionized in an ESI plume and then detected by an ion trap mass analyzer. This TLC/LIAD/ESI/MS approach allowed the components in mixtures of dye standards, drug standards, and rosemary essential oil to be separated and rapidly characterized.