A rotating ball inlet for on-line MALDI mass spectrometry

The rotating ball inlet (ROBIN) is presented in a new design for on-line matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS). This method uses a capillary to deliver a matrix and analyte solution to the surface of a rotating ball upon which MALDI is carried out. The ball is in contact with a polymer gasket surrounding the capillary. Sample adhering to the surface of the ball is dragged past the gasket into the vacuum of the mass spectrometer where it is irradiated by a pulsed UV laser, and the resulting ions are mass-separated in a linear time-of-flight mass spectrometer. The mechanical sample introduction prevents clogging of the vacuum interface by matrix crystals or frozen solvent. Preliminary results from flow injection analysis (FIA) suggest that the new interface does not introduce a significant peak-tailing or memory effect. The system is capable of 20-30 h of continuous operation with a flow rate of 2 microL/min before cleaning of the ball is needed. With the prototype inlet, concentration detection limits are at the low micromolar level.     

Impulse-driven heated-droplet deposition interface for capillary and microbore LC-MALDI MS and MS/MS

An automated off-line liquid chromatography-matrix-assisted laser desorption ionization (LC-MALDI) interface capable of coupling both capillary and microbore LC separations with MALDI mass spectrometry (MS) and tandem mass spectrometry (MS/MS) has been developed. The interface is a combination of two concepts: analyte concentration from heated hanging droplets and impulse-driven droplet deposition of LC fractions onto a MALDI sample plate. At room temperature the interface allows the coupling of capillary LC separations (i.e., flow rate of <5 microL/min) with MALDI MS. With heating, it can be used to combine microbore LC operated at a relatively high flow rate of up to 50 microL/min with MALDI MS. The collected fractions can be analyzed by MALDI MS and MS/MS instruments, such as time-of-flight (TOF) and quadrupole-TOF MS. Performance of the interface was examined using several peptide and protein standards. It was shown that, using MALDI-TOF MS, [GLU1]-fibrinopeptide B could be detected with a total injection amount of 5 fmol to microbore LC. Chromatographic performance was also monitored. A peak width of 12 s at half-height for [GLU1]-fibrinopeptide B showed no evidence of band broadening due to the interface. The ability of the interface to mitigate ion suppression was studied using a mixture of 100 fmol of [GLU1]-fibrinopeptide B and 10 pmol of cytochrome c tryptic digest. Although fully suppressed under direct MALDI conditions, LC-MALDI analysis was able to detect the 100 fmol peptide with 10 s fraction collection. Finally, the ability to inject relatively large sample amounts to improve detectability of low-abundance peptides was illustrated in the analysis of phosphopeptides from alpha-casein tryptic digests. A digest loaded on column to 2.4 microg and analyzed by LC-MALDI MS/MS resulted in 82% sequence coverage and detection of all nine phosphoserine residues. It is concluded that, being able to handle both high- and low-flow LC separations, the impulse-driven heated-droplet interface provides the flexibility to carry out MALDI analysis of peptides and proteins depending on the information sought after, analysis speed, and sample size.     

Surface- and interface oscillations of a rotating viscous liquid column of immiscible liquids

The natural damped coupled frequencies of a rotating viscous infinite liquid column with no axial dependency (∂/∂z=0) have been determined. The frequency equation is presented for a single liquid column, an annular liquid column around a rotating rigid center core, two immiscible liquids with a free- and interfacial surface and also for two immiscible liquids in a rigid container. Only the rotating single liquid column was evaluated numerically and exhibited a rather surprising result. It was found that a viscous column is less stable than that consisting of frictionless liquid. In addition it was found that the conjugate complex roots for each mode in the non-rotating case become two complex roots which are no longer conjugate complex and that the purely decaying roots in the non-rotating case turn into complex roots for rotating liquid, exhibiting damped oscillations.     

High-speed, high-resolution monolithic capillary LC-MALDI MS using an off-line continuous deposition interface for proteomic analysis

High-speed, high-resolution LC separations, using a poly(styrene-divinylbenzene) monolithic column, have been coupled to MALDI MS and MS/MS through an off-line continuous deposition interface. The LC eluent was mixed with alpha-cyano-4-hydroxycinnamic acid matrix solution and deposited on a MALDI plate that had been precoated with nitrocellulose. Deposition at subatmospheric pressure (80 Torr) formed a 250-microm-wide serpentine trace with uniform width and microcrystalline morphology. The deposited trace was then analyzed in the MS mode using a MALDI-TOF/TOF MS instrument. Continuous deposition allowed interrogation of the separation with a high data sampling rate in the chromatographic dimensions, thus preserving the high resolution of narrow peaks (3-5-s peak width at half-height) of the fast monolithic LC. No extracolumn band broadening due to the deposition process was observed. Over 2000 components were resolved in a 10-min linear gradient separation of the model sample, and 386 unique peptides were identified in the subsequent MS/MS analysis. The continuous deposition interface allows the coupling of high-resolution separations to MALDI MS without degradation in separation efficiency, thus enabling high-throughput proteome analysis.     

Automated iterative MS/MS acquisition: a tool for improving efficiency of protein identification using a LC-MALDI MS workflow

We have developed an information-dependent, iterative MS/MS acquisition (IMMA) tool for improving MS/MS efficiency, increasing proteome coverage, and shortening analysis time for high-throughput proteomics applications based on the LC-MALDI MS/MS platform. The underlying principle of IMMA is to limit MS/MS analyses to a subset of molecular ions that are likely to identify a maximum number of proteins. IMMA reduces redundancy of MS/MS analyses by excluding from the precursor ion peak lists proteotypic peptides derived from the already identified proteins and uses a retention time prediction algorithm to limit the degree of false exclusions. It also increases the utilization rate of MS/MS spectra by removing "low value" unidentifiable targets like nonpeptides and peptides carrying large loads of modifications, which are flagged by their "nonpeptide" excess-to-nominal mass ratios. For some samples, IMMA increases the number of identified proteins by ～20-40% when compared to the data dependent methods. IMMA terminates an MS/MS run at the operator-defined point when "costs" (e.g., time of analysis) start to overrun "benefits" (e.g., number of identified proteins), without prior knowledge of sample contents and complexity. To facilitate analysis of closely related samples, IMMA's inclusion list functionality is currently under development.     

Ultrasensitive proteomics using high-efficiency on-line micro-SPE-nanoLC-nanoESI MS and MS/MS

Ultrasensitive nanoscale proteomics approaches for characterizing proteins from complex proteomic samples of <50 ng of total mass are described. Protein identifications from 0.5 pg of whole proteome extracts were enabled by ultrahigh sensitivity (<75 zmol for individual proteins) achieved using high-efficiency (peak capacities of approximately 10(3)) 15-microm-i.d. capillary liquid chromatography separations (i.e., using nanoLC, approximately 20 nL/min mobile-phase flow rate at the optimal linear velocity of approximately 0.2 cm/s) coupled on-line with a micro-solid-phase sample extraction and a nanoscale electrospray ionization interface to a 11.4-T Fourier transform ion cyclotron resonance (FTICR) mass spectrometer (MS). Proteome measurement coverage improved as sample size was increased from as little as 0.5 pg of sample. It was found that a 2.5-ng sample provided 14% coverage of all annotated open reading frames for the microorganism Deinococcus radiodurans, consistent with previous results for a specific culture condition. The estimated detection dynamic range for detected proteins was 10(5)-10(6). An improved accurate mass and LC elution time two-dimensional data analysis methodology, used to both speed and increase the confidence of peptide/protein identifications, enabled identification of 872 proteins/run from a single 3-h nanoLC/FTICR MS analysis. The low-zeptomole-level sensitivity provides a basis for extending proteomics studies to smaller cell populations and potentially to a single mammalian cell. Application with ion trap MS/MS instrumentation allowed protein identification from 50 pg (total mass) of proteomic samples (i.e., approximately 100 times larger than FTICR MS), corresponding to a sensitivity of approximately 7 amol for individual proteins. Compared with single-stage FTICR measurements, ion trap MS/MS provided a much lower proteome measurement coverage and dynamic range for a given analysis time and sample quantity.     

A bulk electrolysis Raman spectroelectrochemical cell using a rotating electrode

A fast bulk electrolysis Raman spectroelectrochemical cell is described. The cell employs a large-area platinum gauze and disk assembly which can be rotated at speeds up to 5,000 rpm. The complete electrolysis of a 5-mL solution can be achieved in less than 6 min using a 2,000 rpm rotation rate. The resonance Raman spectrum of (TPP*+)Cu(II) was collected in situ in this cell.     

DNA microarray enhancement using a continuously and discontinuously rotating microchamber

It is demonstrated that the most efficient way to enhance DNA microarray analysis consists of a maximal reduction of the total device volume (to keep the concentration of the available DNA as high as possible), combined with the creation of a strong lateral convective transport of the sample. In the present study, DNA microarray hybridizations are performed in a set of rotating, circular microchambers covering exactly the spotted area of the microarray and with a depth varying between 70 and 1.6 microm. Rotating the microchamber substrate while keeping the microarray stationary, the rotating microchamber bottom wall literally drags the sample past the microarray spots with a velocity which is independent of the fluid layer thickness. Interestingly, it was found that transporting the sample in a discontinuous mode (with stop periods of several minutes) not only yields a more stable and reproducible operation, it also yields significantly larger hybridization intensities (typically a factor of 2-3 larger) than a continuous rotation. This seems to be due to the fact that the velocity field disturbs the binding process at the binding site level. Working under limiting DNA sample mass conditions, the system yielded in a short, 30-min experiment already a 5-fold increase of the hybridization intensity, as compared to a conventional microscope slide/coverslip system operated overnight under diffusion-driven conditions. Compared to a commercial pump-around hybridization system, the gain was even more impressive, precisely due to the fact that the pump-around system requires larger volumes, which with a fixed amount of available genetic material leads to the application of more diluted samples.     

Online short-term reliability evaluation using a fast sorting technique

To consider time varying system operating conditions and operating reserve units, the online short-term reliability of a power system is investigated. Real-time system reliability based on the online operation data provided by the SCADA/EMS/WAMS is assessed using time- dependent state probabilities of components. Considering both speed and accuracy requirements, a fast sorting technique (FST) is proposed to quickly select the required number of system states in descending order probability. The number of computations and comparisons used in the evaluation is minimum. The relative accuracy of a given reliability index is denned as the stopping rule for the evaluation. As only a small number of system states are required to achieve the high accuracy of the short-term reliability indices when using the FST, the evaluation can be performed in an online environment. The proposed evaluation technique is illustrated by the application to the IEEE-RTS and China Southern Power Grid.     

Completely flat erosion magnetron sputtering using a rotating asymmetrical yoke magnet

A completely flat erosion magnetron 5-inch cathode has been developed for planer magnetron sputtering using a rotating asymmetrical yoke magnet. The yoke magnet was composed of an iron yoke base with a 70 mm diameter, an annular outer yoke, a center Fe-Nd-B magnet which was shifted from the yoke base center, and an assisted Fe-Nd-B magnet which was attached to a part of the outer yoke. In order to optimize the magnetic flux density for uniform target erosion from center to outer area, several diameters of the center Fe-Nd-B magnet, from 25 to 36 mm, were tested by the first experiment, and secondly the outer yoke structure was optimized using the first experimental results. The obtained final target utilization was 77% and erosion depth uniformity for the 4-inch diameter was ±6%.     

Digital holographic scanning of large objects using a rotating optical slab

Simple optical glass is used in digital holographic set up to scan and record holograms of a large object. Dimension of the object is such that it does not satisfy sampling theorem. Experimental results and calculations illustrate that an optical slab can be used to scan the surface of the large object by this method. © 2007 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 16, 258–261, 2006     

Completely flat erosion magnetron sputtering using a rotating asymmetrical yoke magnet

A completely flat erosion magnetron 5-inch cathode has been developed for planer magnetron sputtering using a rotating asymmetrical yoke magnet. The yoke magnet was composed of an iron yoke base with a 70 mm diameter, an annular outer yoke, a center Fe-Nd-B magnet which was shifted from the yoke base center, and an assisted Fe-Nd-B magnet which was attached to a part of the outer yoke. In order to optimize the magnetic flux density for uniform target erosion from center to outer area, several diameters of the center Fe-Nd-B magnet, from 25 to 36 mm, were tested by the first experiment, and secondly the outer yoke structure was optimized using the first experimental results. The obtained final target utilization was 77% and erosion depth uniformity for the 4-inch diameter was ±6%.     

Independent control of ion transmission in a jet disrupter dual-channel ion funnel electrospray ionization MS interface

A new atmospheric pressure ionization mass spectrometer (API-MS) interface has been developed to allow the control of ion transmission through the first vacuum stage of the mass spectrometer. The described interface uses a dual-heated capillary and a dual-inlet ion funnel design. Two electrosprays, aligned with the dual-capillary inlet, are used to introduce ions from different solutions independently into the MS. The initial design was specifically aimed at developing a method for the controlled introduction of calibrant ions in highly accurate mass measurements using Fourier transform ion cyclotron resonance mass spectrometer (FTICR). The dual-channel ion funnel has different inlet diameters that are aligned with the dual capillaries. The large diameter main channel of the ion funnel is used for analyte introduction to provide optimum ion transmission. The second, smaller diameter channel inlet includes a jet disrupter in the ion funnel to modulate the ion transmission through the channel. The two inlet channels converge into a single-channel ion funnel where ions from both channels are mixed, focused, and transmitted to the mass analyzer. Both theoretical simulations and experimental results show that the transmission of different m/z species in the small diameter channel of the ion funnel can be effectively modulated by varying the bias voltage on the jet disrupter. Both static and dynamic modulations of ion transmission are demonstrated experimentally by applying either a constant DC or a square waveform voltage to the jet disrupter. High ion transmission efficiency, similar to the standard single-channel ion funnel, is maintained in the main analyte channel inlet of the ion funnel over a broad m/z range with negligible "cross talk" between the two ion funnel inlet channels. Several possible applications of the new interface (e.g., for high-accuracy MS analysis of complex biological samples) are described.     

Optimization of a nanoparticle ball milling process parameters using the response surface method

Nanocrystalline TiO₂-CeO₂ powders were synthesized from their TiO₂ and CeO₂ oxides using mechanical ball milling process. The response surface method is applied to identify optimal parameters for the synthesis of TiO₂-CeO₂ photocatalyst. Analysis of variance and main effect plot are used to determine the significant parameters and set the optimal level for each parameter. Regression analysis showed good agreement of experimental data with the second-order polynomial model with a coefficients of determination: R²?=?0.991, R²_Adj.?=?0.940 and R²_Pred.?=?0.983. Under optimal experimental conditions of TiO₂:CeO₂ weight percentage ratio 71:29, milling speed 200?rpm, and milling time 115?min the highest photodegradation efficiency was achieved. On the basis of the above statistical analysis, it was found that the band gap energy of TiO₂-CeO₂ nanoparticles decreases with the increase of the milling speed and milling time with constant TiO₂:CeO₂ weight percentage ratio. Obtained results suggest that mechanical ball milling process is a rapid, efficient and low energy consumption method to synthesize TiO₂-CeO₂ photocatalyst.     

Numerical approximation of a thermally driven interface using finite elements

A two‐dimensional finite element model for dendritic solidification has been developed that is based on the direct solution of the energy equation over a fixed mesh. The model tracks the position of the sharp solid–liquid interface using a set of marker points placed on the interface. The simulations require calculation of the temperature gradients on both sides of the interface in the direction normal to it; at the interface the heat flux is discontinuous due to the release of latent heat during the solidification (melting) process. Two ways to calculate the temperature gradients at the interface, evaluating their interpolants at Gauss points, were proposed. Using known one‐ and two‐dimensional solutions to stable solidification problems (the Stefan problem), it was shown that the method converges with second‐order accuracy. When applied to the unstable solidification of a crystal into an undercooled liquid, it was found that the numerical solution is extremely sensitive to the mesh size and the type of approximation used to calculate the temperature gradients at the interface, i.e. different approximations and different meshes can yield different solutions. The cause of these difficulties is examined, the effect of different types of interpolation on the simulations is investigated, and the necessary criteria to ensure converged solutions are established. Copyright © 2003 John Wiley & Sons, Ltd.     

Picoliter rheology of gaseous media using a rotating optically trapped birefringent microparticle

An optically trapped birefringent microparticle is rotated by a circularly polarized beam in a confined gaseous medium. By recording the terminal rotation velocity and the change in polarization of the incident trapping beam, we determine the viscosity by probing a picoliter volume of air, carbon dioxide, and argon in the vicinity of the microparticle. We also characterize the optical force acting on a trapped particle in air using the generalized Lorenz-Mie theory taking into account the aberrations present. This opens up a new potential application of optical tweezers for the accurate measurement of gas viscosity in confined geometries.     

Model updating of a rotating machine using the self-adaptive differential evolution algorithm

Despite the good accuracy of finite element (FE) models to represent the dynamic behaviour of mechanical systems, practical applications show significant discrepancies between analytical predictions and experimental results, which are mostly due to uncertainties on the geometry configuration, imprecise material parameters and vague boundary conditions. Thereby, different approaches have been proposed to solve the inverse problems associated with the updating of FE models. Among them, the techniques based on minimization processes have shown to be some of the most promising ones. In this paper, a self-adaptive heuristic optimization method, namely the self-adaptive differential evolution (SADE), is evaluated. Differently from the canonical differential evolution (DE) algorithm, the SADE strategy is able to update dynamically the required parameters such as population size, crossover parameter and perturbation rate. This is done by considering a defined convergence rate on the evolution process of the algorithm in order to reduce the number of evaluations of the objective function. For illustration purposes, the SADE strategy is applied to the solution of typical mathematical functions. Additionally, the strategy is equally used to update the FE model of a rotating machine composed by a horizontal flexible shaft, two rigid discs and two unsymmetrical bearings. For comparison purposes, the canonical DE is also used. The results indicate that the SADE algorithm is a recommended technique for dealing with this kind of inverse problem.