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.     

Interfaces to connect thin-layer chromatography with electrospray ionization mass spectrometry

This study has developed two interfaces to connect small-size thin-layer chromatography (TLC) with electrospray ionization mass spectrometry (ES-MS) for the continuous analysis of organic mixtures. The interfaces are (1) two bound optical fibers inserted into the C18-bonded particles at the exit of a small TLC channel and (2) a small commercial TLC strip with a sharpened tip. A reservoir continuously supplied a makeup solution to the tip of the TLC channel. The high voltage required for electrospray ionization was introduced into the makeup solution or mobile phase through a Pt wire, and electrospray was generated at the tip of the bonded optical fibers and at the sharp end of the TLC strip. Since small-size TLC channels were used, the elution time was short and less than 0.2 microL of the sample solution and 200 microL of the eluting solvent were required. Organic mixtures were separated successfully and detected on-line using the TLC/ES-MS techniques.     

Use of a water-soluble fullerene derivative as precipitating reagent and matrix-assisted laser desorption/ionization matrix to selectively detect charged species in aqueous solutions

A starlike water-soluble fullerene derivative, hexa(sulfonbutyl)fullerene (C60[(CH2)4SO3-]6; HSBF), consisting of a C60 cage covalently bonded with six negatively charged sulfonate arms, was synthesized and used to selectively precipitate positively charged surfactants, amino acids, peptides, and proteins. The affinity of HSBF to the analytes depends on the charge, structure, and hydrophobic characteristics of the analytes. The ion pair precipitate was easily removed from the solution by centrifugation. After washing, the precipitate was redissolved in the solvent or buffer solution and the analyte was characterized by laser desorption ionization-time-of-flight mass spectrometry (LD-TOF). HSBF shows strong optical absorbance in the UV range, so no additional organic matrix was required to conduct LD-TOF analysis of small analytes. For the solution that contained five quaternary amines differing only in alkyl chain length, HSBF exhibits the highest affinity to the amine with the longest alkyl chain. Only the arginine signal was detected from the solution that contained 14 amino acids. The peptides with arginine as the end groups interacted most strongly with HSBF and could be selectively precipitated from a solution of a mixture of five peptides. The signals associated with a trace amount of charged peptides derived from the digestion of proteins by trypsin were greatly enhanced after concentration with HSBF. Among eight proteins in the sample solution, insulin had the strongest affinity to the HSBF and exhibited the strongest signal on the matrix-assisted laser desorption/ionization mass spectrum.     

Gas chromatography connected to multiple channel electrospray ionization mass spectrometry for the detection of volatile organic compounds

This work successfully connected gas chromatography (GC) to seven-channel electrospray ionization (ESI) mass spectrometry to separate and detect a mixture of volatile organic compounds. Gaseous analyte was eluted separately from a GC column and directed into the central channel of the ESI source. The analyte was protonated by ion-molecule reactions between the analyte and the ions which were generated by electrospraying the acidic solution through the outside six channels surrounding the central channel. Real-time analysis of the organic reaction involving volatile and thermally unstable compounds (dimethylhydrazine ? azomethane + H(2)) was also achieved by continuously purging the air in the reaction vessel to the seven-channel ESI source.     

Generating multiply charged protein ions by ultrasonic nebulization/multiple channel-electrospray ionization mass spectrometry.

An ultrasonic nebulization/multiple channel electrospray ionization (USN/MC-ES) source, which generates multiply charged peptides and proteins ions, was developed. The source is an ultrasonic nebulizer that is connected to a multiple channel electrospray ionization source. Aerosols were formed by ultrasonically nebulizing the sample solution. The aerosols were then purged into the central channel of a seven-channel ES source via nitrogen gas. A methanol solution that contained 1% trifluroacetic acid was electrosprayed through the outlying six electrosprayers. Detection of multiply charged peptide and protein ions indicated that electrospray was generated from the charged droplet containing analyte. The sample aerosol appeared to fuse with the charged methanol droplet in the air. Then electrospray ionization of the analyte occurred from the newly formed droplet. The peptide and protein prepared in deionized water were detected by this USN/MC-ES-MS. By varying the electrospray solvents, the signals of certain components in the mixture were selectively suppressed.     

A post-bonding-free fabrication of integrated microfluidic devices for mass spectrometry applications

This paper presents a novel process for fabricating integrated microfluidic devices with embedded electrodes which utilizes low-cost UV curable resins. Commercial UV glue is sandwiched between two substrates and is used for both the structural material and the bonding adhesive. During the exposure procedure, the pattern of micro-fluidic channels is defined using a standard lithography process while the two substrates are bonded. The un-cured UV glue is then removed by vacuum suction to form the sealed microfluidic channel. With this simple approach, conventional high-temperature bonding processes can be excluded in the fabrication of sealed microfluidic structures such that the developed method is highly advantageous for fabricating microchip devices with embedded electrodes. The overall time required to fabricate the sealed microchip device is less than 10 min since no time-consuming etching and bonding process is necessary. An innovative micro-reactor integrated with an in-channel micro-plasma generator for real-time chemical reaction analysis is fabricated using the developed process. On-line mass-spectrum (MS) detection of an esterification reaction is successfully demonstrated, which results in a fast, label-free, preparation-free analysis of chemical samples. The developed process can thus show its potential for rapid and low-cost microdevice manufacturing.     

Predicting Transition Velocities from Bubbling to Turbulent Fluidization by S-Statistics on Vibration Signals

Vibration signatures as the representatives of the fluidized bed nonlinear hydrodynamics were measured in a lab-scale fluidized bed of sand particles operated at ambient conditions. The experiments were carried out for three particle sizes, different velocities, and three probe heights. The S-statistic method was applied to the vibration signatures for the chaotic attractor comparison. The measured signatures of two different consecutive velocities in similar conditions were compared based on null hypothesis that they have same origin. According to this method, when the value of S is larger than 3, the null hypothesis is rejected with the confidence level of 95% indicating that the two signals are originated from different hydrodynamics. The results are compared with results obtained from common statistical methods and it is shown that attractor comparison can be a reliable method for detecting regime transition velocity.     

Evaluation of Hydrodynamic Closures for Bubbly Regime CFD Simulations in Developing Pipe Flow

The effect of interfacial forces and relevant closures, particularly the lift and wall lubrication forces, on the predictions of Eulerian‐Eulerian computational fluid dynamics simulations of bubbly flows was studied. The test case under study was a developing turbulent bubbly pipe flow, simulated by using OpenFOAM. The results show that the geometric approach to consider the wall effect leads to better agreement than a standard relation assuming asymmetric drainage around the bubble near the wall. Furthermore, the results verify the need for employing negative lift coefficients in cases with large bubbles. A sensitivity analysis on the lift coefficient highlighted the importance of investigating spatially developing flows to draw general conclusions on the applicability of closure relations.     

Building blocks for the development of an interface for high-throughput thin layer chromatography/ambient mass spectrometric analysis: a green methodology

Interfacing thin layer chromatography (TLC) with ambient mass spectrometry (AMS) has been an important area of analytical chemistry because of its capability to rapidly separate and characterize the chemical compounds. In this study, we have developed a high-throughput TLC-AMS system using building blocks to deal, deliver, and collect the TLC plate through an electrospray-assisted laser desorption ionization (ELDI) source. This is the first demonstration of the use of building blocks to construct and test the TLC-MS interfacing system. With the advantages of being readily available, cheap, reusable, and extremely easy to modify without consuming any material or reagent, the use of building blocks to develop the TLC-AMS interface is undoubtedly a green methodology. The TLC plate delivery system consists of a storage box, plate dealing component, conveyer, light sensor, and plate collecting box. During a TLC-AMS analysis, the TLC plate was sent to the conveyer from a stack of TLC plates placed in the storage box. As the TLC plate passed through the ELDI source, the chemical compounds separated on the plate would be desorbed by laser desorption and subsequently postionized by electrospray ionization. The samples, including a mixture of synthetic dyes and extracts of pharmaceutical drugs, were analyzed to demonstrate the capability of this TLC-ELDI/MS system for high-throughput analysis.     

Polyfunctional Fullerene Derivatives as UV-MALDI Matrices to Detect Peptides and Proteins

Abstract

Fullerene derivatives with polyfunctional groups were synthesized and used as matrices in UV matrix-assisted laser desorption ionization (UV-MALDI) to detect polar biomolecules such as peptides and proteins. The fullerene derivatives are N,N-dimethylformamide (DMF) or water soluble. The matrix solutions (in DMF or water) can mix well with the aqueous solution containing the analyte. Visual observation with the assistance of magnifying glasses indicated that after drying, a homogenous sample solution was produced on the sample probe. MALDI/time-of-flight (MALDI/TOF) analyses results demonstrate that strong signals from peptides and proteins can be obtained. The fact that a homogenous sample solution was produced on the sample probe accounts for why the analyte's signals were detected everywhere on the probe.