J.C.M. Marijnissen

JET BREAK-UP IN ELECTROHYDRODYNAMIC ATOMIZATION IN THE CONE-JET MODE

The jet break-up mechanism has been investigated with a high-resolution camera . A model is presented, which is able to predict the droplet size, the velocity at jet break-u p, and the wavelength at jet break-up. A new theoretical derivation of the droplet size scaling will be given. It was found that the jet break-up mechanism depends on the ratio of the electric normal st ress over the surface tension stress. At a low value of this ratio, the jet breaks up due to varicose instabilities. The number of secondary droplets is much lower than the number of main droplets. With increasing flow rate, the current increases, the stress ratio increases, and the number of secondary dro plets and satellites increases. A threshold value of the stress ratio on the jet was found, above which the jet starts to whip. In order to reduce the number of secondary droplets, the current through the liquid cone should be reduced. It is shown, that viscosity, surface charge, and the acceleration of the jet, have to be taken into account in the jet break-up process. The main droplet diameter for varicose jet break-up scales with the flow rate as dd=Q0.48. When, the jet breaks up in the whipping regime, then the main droplet size scales as dd=Q0.33.

Application of matrix‐assisted laser desorption/ionization to on‐line aerosol time‐of‐flight mass spectrometry

Matrix-assisted laser desorption/ionization (MALDI) mass spectra were obtained from single biological aerosol particles using an aerosol time-of-flight mass spectrometer (ATOFMS). The inlet to the ATOFMS was coupled with an evaporation/condensation flow cell that allowed the aerosol to be coated with matrix material as the sampled stream entered the spectrometer. Mass spectra were generated from aerosol composed either of gramicidin-S or erythromycin, two small biological molecules, or from aerosolised spores of Bacillus subtilis var niger. Three different matrices were used: 3-nitrobenzyl alcohol, picolinic acid and sinapinic acid. A spectrum of gramicidin-S was generated from approximately 250 attomoles of material using a molar ratio of 3-nitrobenzyl alcohol to analyte of approximately 20:1. A single peak, located at 1224 Da, was obtained from the bacterial spores. The washing liquid and extract solution from the spores were analyzed using electrospray mass spectrometry and subsequent MS/MS product ion experiments. This independent analysis suggests that the measured species represents part of the B. subtilis peptidoglycan. The on-line addition of matrix allows quasi-real-time chemical analysis of individual, aerodynamically sized particles, with an overall system residence time of less than 5 seconds. These results suggest that a MALDI-ATOFMS can provide nearly real-time identification of biological aerosols. Copyright 2000 John Wiley & Sons, Ltd.

Restriction for the ELPI in diesel particulate measurements

A dynamic phenomenon that occurs with the measurement of a diluted diesel-soot aerosol with an electrical low-pressure impactor (ELPI) was studied. An experimental setup for measuring the performance of diesel particulate filters was used for this purpose. Impactor overloading is thought to be responsible for this dynamic phenomenon. SEM analysis indicates that the fluffy or fractal structure of the diesel-soot aerosol is responsible for rapid overloading. A fluffy bed of particles on the impactor surface filters the particle-laden gas stream as it passes over the impactor surface. This phenomenon could lead to improper use of the ELPI and thereby it poses a restriction for this application. Users in the field should be aware of this phenomenon because the transient response signal from the ELPI could easily be misinterpreted as a start-up effect whereas, in reality, the ELPI is used improperly. The use of oil-soaked sintered collectors can be a solution for this problem.

Oil-soaked sintered impactors for the ELPI in diesel particulate measurements

Diesel soot overloads the ELPI-impactor rapidly if it is equipped with the standard flat-surface impactors. This non-ideal behaviour was studied recently (J. Aerosol Sci. 32 (2001) 1117). It was found that rapid overloading, or surface build-up, is a result of a fluffy bed of soot particles that covers the impactor surfaces and starts to filter airborne soot particles. This paper reports additional results with oil-soaked sintered impactors for the ELPI. It is demonstrated that (rapid) overloading is eliminated with oil-soaked sintered impactors. The maximum allowed mass load for the ELPI impactor is increased 50-fold.

Fluorescence preselection of bioaerosol for single-particle mass spectrometry.

We have designed, constructed, and tested a system that pre-selects the biological fraction of airborne particles from the overall aerosol. The preselection is based on fluorescence emission excited by a continuous 266 nm laser beam. This beam is one of two cw beams used to measure the aerodynamic particle size of sampled particles. The intention in our system is that single particles, based on size and fluorescence emission, can be selected and further examined for chemical composition by mass spectrometry.

Renewable energy liberation by nonthermal intermolecular bond dissociation in water and ethanol

Prior indication that renewable energy can be extracted from hydrogen bonds in water has led to several investigations of the energy balance when bulk liquid is converted into micron scale droplets by directional (nonthermal) forces. The demonstration of this effect has previously involved pulsed high current arcs in water which produce large electrodynamic forces. Here, we show that renewable energy is also liberated during the creation of droplets by electrostatic forces in electrohydrodynamic atomization (electrospray) experiments. Using both ethanol and water, the energy outputs, primarily the droplet kinetic energy, were always greater than the energy inputs, implying that stored energy was liberated from the liquid. The energetics of generic chemical bonding are investigated to demonstrate that although this discovery was not publicly anticipated, it is consistent with conventional theory. This experimental breakthrough should have a major impact on the quest for renewable energy sources, capable of...

Development of Bioaerosol Alarming Detector

Although banned by the BTWC in 1972, biological warfare agents continue to be a threat to military and public health. Countermeasures can only be effective if rapid detection and reliable identification techniques are in place. TNO Prins Maurits Laboratory, and Delft University of Technology and Bruker-Daltonik (Germany) are developing an bioaerosol alarm detector, based on fluorescence pre-selection, Aerosol Time-of-Flight Mass Spectrometry (ATOFMS) and Matrix-Assisted Laser Desorption/Ionization (MALDI). Using this combination, mass spectra were obtained from single biological aerosol particles.

On-line tof-mass-spectrometry of aerosols: System characterisation

J.C.M. MARIJNISSEN, B. SCARLETT Delft University of Technology, Faculty of Chemical Technology, Julianalaan 136, 2628 BL Delft, The Netherlands KEYWORDS Laser mass spectrometry, aerosol beam, single particle analysis INTRODUCTION At Delft University of Technology an instrument has been developed to chemically characterise single particles in an aerosol. Chemical analysis of single particles can, for example, be useful to determine the origin of a particle. However, analysing a sufficient number of particles is very time consuming if sample preparation is necessary. Therefore an on-line and real time system is very helpful for such investigations. The applicability is under investigation. In the field of aerosol science, it could for example be used in quality control of aerosol products and atmosphere monitoring. INSTRUMENTATION The instrument (figure 1) has been proposed by Marijnissen et al. (1988). Aerosol particles are introduced into the vacuum chamber of a time of flight mass spectrometer by a differ- entially pumped nozzle system (Kie- vit et al., 1990). With the aid of a continuous HeNe laser the particles are detected and sized by light scat- tering techniques. A 5 mJ excimer laser, triggered by the optical parti- cle detection system, fires approxi- mately 1 Its later, vaporizes the par- ticles and ionizes the resulting frag- ments. The ions are then analysed in a TOF mass spectrometer. The

Experiment and Simulation of Electrospray Particle-Flows for Controlled Release of Drugs

Electro HydroDynamic Atomisation (EHDA) disperses a liquid into small, highly charged droplets. We show that this method can be used to produce particles that release a drug at a desired rate. This is done by spraying a solution of bio-degradable polymers and an enzyme, which represents the effective drug. The release rate can be varied by modification of the polymer matrix. It is further demonstrated that the enzyme fully retains its functionality in the EHDA process. Practical use of this technique for medicine production requires a scaled-up design, which must be based on an adequate model of the particle flow in the charged droplet spray plume. As a step in this direction, the most important result is a scale-up relation that allows simulations of an experimental spray with millions of particles, using only a few thousand model particles. The experimental spray is examined with a Phase Doppler Particle Analyser (PDPA) set-up, and the resulting density and velocity profiles are compared to the numerical results. There is a qualitative agreement between experiment and model.