Francisco J. Romay

Next Generation Pharmaceutical Impactor (A New Impactor for Pharmaceutical Inhaler Testing). Part I: Design

A new cascade impactor has been designed specifically for pharmaceutical inhaler testing. This impactor, called the Next Generation Pharmaceutical Impactor (NGI), has seven stages and is intended to operate at any inlet flow rate between 30 and 100 L/min. It spans a cut size (D50) range from 0.54-microm to 11.7-microm aerodynamic diameter at 30 L/min and 0.24 microm to 6.12 microm at 100 L/min. The aerodynamics of the impactor follow established scientific principles, giving confident particle size fractionation behavior over the design flow range. The NGI has several features to enhance its utility for inhaler testing. One such feature is that particles are deposited on collection cups that are held in a tray. This tray is removed from the impactor as a single unit, facilitating quick sample turn-around times if multiple trays are used. For accomplishing drug recovery, the user can add up to approximately 40 mL of an appropriate solvent directly to the cups. Another unique feature is a micro-orifice collector (MOC) that captures in a collection cup extremely small particles normally collected on the final filter in other impactors. The particles captured in the MOC cup can be analyzed in the same manner as the particles collected in the other impactor stage cups. The user-friendly features and the aerodynamic design principles together provide an impactor well suited to the needs of the inhaler testing community.

Experimental Study of Electrostatic Capture Mechanisms in Commercial Electret Filters

ABSTRACT Electret filters are widely used in applications requiring high-filtration efficiency and low-pressure drop. These filters rely on electrostatic particle capture mechanisms in addition to the conventional mechanical capture mechanisms. This study reports experimental data collected on the performance of three types of commercially available fibrous electret filters: corona-charged fibrillated split-fiber media (type A), triboelectrically charged mixed-fiber media (type B) and corona-charged meltblown media (type C). The filtration efficiency of these filters was measured as a function of particle size (i.e., 0.05 to 0.5 μm) and charge state (i.e., singly charged and neutral) for two face velocities. The same experiments also were performed on discharged electret filters to obtain information on the pure mechanical capture mechanisms. The magnitude of the effective surface electric field for each tested electret filter was estimated from a simplified Coulombic capture model, giving information on ...

Particle Charge Distribution Measurement for Commonly Generated Laboratory Aerosols

ABSTRACT An improved particle charge analyzer system has been developed to measure the absolute charge distribution of common generated laboratory aerosols. The charge analyzer system consists of an integral cylindrical mobility analyzer used in conjunction with an optical aerosol spectrometer, with computer assisted operation and data reduction. The charge analyzer collects aerosol particles over an absolute electrical mobility range from 4.2*10−4 to 400 cm2/(stat · Volt second) and flow rates that can vary from 0.3 to 30 liters per minute. The charge analyzer has been used to investigate the nature of spray and contact electrification during aerosol generation by measuring the residual charge distribution on the liquid and solid generated particles. In addition, the neutralization of charged particles by bipolar ions also was studied using conventional neutralizers that use ionizing radiation from alpha and beta sources. Charge distribution measurements were performed on alumina dust (Al), Arizona road ...

On the Combination Coefficient of Positive Ions with Ultrafine Neutral Particles in the Transition and Free-Molecule Regimes

The charged fraction of ultrafine silver particles (5–50 nm) suspended in high-purity helium (99.998% grade) was measured as a function of particle size under different charging conditions (i.e., ion concentration and charging time). The charger used is a modified version of the one described in a previous study (Romay et al., 1991). Two radioactive sources of 250 μCi Po-210 are located in a cavity at the charger inlet. The cavity configuration is designed to control the range of the α rays. The modified charger provides a uniform electric field in the axial direction to separate the positive ions from the negative ions and electrons produced by the ionizing radiation. Thus, the aerosol particles are first exposed to a small region of electrons and positive ions, and are subsequently charged by positive ions in a much longer section of the charger. The ion concentration is estimated from the ion current collected in the exit electrode and measured with a picoammeter. The charging time is estimated from th...

A Sonic Jet Corona Ionizer for Electrostatic Discharge and Aerosol Neutralization

A sonic jet bipolar ionizer has been designed and tested. Ion production rates and characteristics of particulate contaminants were studied as a function of design parameters (i.e., electrode material, and orifice plate material) and of operating conditions (i.e., electrode to orifice distance, pressure, electrode voltage). In the optimized design particle generation by electrode or plate sputtering was eliminated, while particle generation by chemical reaction and subsequent gas to particle conversion was reduced to low levels. The ionizer provided a high output of bipolar ions at rates that ensured balanced operation and low charge neutralization times. An aerosol neutralizer using the corona ionizer was designed and tested with singly charged monodisperse aerosols. The equilibrium charge distribution of the aerosol was measured using an electrical mobility classification technique, and was found to be in good agreement with theoretical predictions.

A High-Performance Aerosol Concentrator for Biological Agent Detection

A particle sampler has been developed, built, and tested. The sampler draws ambient air at approximately 300 L/min and then splits the sampled air into a particle-rich sample stream and a particle-depleted, reject stream. The particle-rich stream contains only 0.3% of the inlet air (i.e., 1-L/min), but 50-90% of the ambient particles in the size range of 2.3 w m to 8.4 w m. This 1-L/min sample stream contains the particles at a concentration of approximately 150-270 times that of the ambient air. For this reason, the sampler is called an aerosol concentrator. By concentrating the particles of interest, we substantially improve the response time and detection limit characteristics of any detector that may be used downstream of the sampler. The aerosol concentrator is a three-stage virtual impactor. The first stage is a scalper drawing nominally 330 L/min of air through a conventional single-nozzle virtual impactor. Particles larger than 10 microns are retained in the 30-L/min minor flow and rejected from the sampler. The remaining 300 L/min of air passes through a two-stage, concentrating virtual impactor (CVI) that splits the flow into a 1-L/min sample stream and a 299-L/min reject stream. The reject stream consists of 285 L/min from the first stage and 14 L/min from the second stage. A blower draws the 299-L/min reject stream and exhausts it through the nozzle of an ejector. The ejector contains a venturi-like tube that aspirates the 30-L/min reject stream from the scalper, making an overall exhaust stream of 329 L/min. Fifty to ninety percent of the particles in the size range of 2.3 microns to 8.4 microns originally in the 300-L/min stream are now contained in the 1 L/min sample stream. The sampler has no valves, and the particles in the 1 L/min sample stream do not encounter a blower, minimizing the losses of particles in the size range of interest. The emphasis on low losses improves the detection limit and speed of detection of the downstream instrumentation and also reduces the frequency of cleaning the sampler.

High-efficiency unipolar aerosol charger using a radioactive alpha source

A new design of a unipolar aerosol charger has been developed. The charger consists of a radioactive source placed between two screen electrodes enclosed by a Plexiglass tube. The electric field in the charger is aligned with aerosol flow. The new charger is capable of charging ultrafine aerosols efficiently and with low particle losses. The charger was evaluated thoroughly both theoretically and experimentally. The basic equations for the charging process in this charger were numerically solved for monodisperse, ultrafine aerosols under various operating conditions. From the calculation results, the particle charge level and loss rate within the charger were found to depend on two dimensionless parameters defined in the paper. In the experiment, the particle charge level and penetration rate were measured for particle sizes of 10–30 nm, operating voltages of 3–9 kV, flow rates of carrier gas of 2–5.21 min−1, and pressures of 0.46 and 1 atm. The experimental results which were obtained under similar conditions estimated by the dimensionless parameters were found to agree with the theoretical predictions. The charger gave a unit charge to 50% of the 10 nm diameter particles with 20% particle losses. The charger was found to work also under low pressure as a high-efficiency charger.

Second generation micro-orifice uniform deposit impactor, 120 MOUDI-II: Design, Evaluation, and application to long-term ambient sampling

The original MOUDI (Micro-Orifice Uniform Deposit Impactor) cascade impactor, reported in the literature in 1991, used an external gear system to achieve a uniform deposit and was intended for industrial hygiene studies with sample times in the range of minutes to a few hours. To facilitate much longer run times, a second generation MOUDI, MOUDI-II, which uses internal electric motors to rotate the impaction plates, was developed. Three model 120 MOUDI-IIs were used in a 32-month program to sample ambient atmospheric aerosols at several industrial and urban locations in Minnesota. For these sampling locations, each 120 MOUDI-II operated continuously for a minimum of five, and optimally 7 days, to collect a sample at a site. During these community sampling events, the three 120 MOUDI-IIs logged 4007, 2637, and 3230 h of operating time, respectively. A laboratory side-by-side comparison of the three 120 MOUDI-IIs showed good agreement amongst the three 120 MOUDI-IIs and, thus, the particle size distributions were independent of the 120 MOUDI-II used. Application of the 120 MOUDI-IIs for long-term ambient sampling was demonstrated by comparing size distributions from the background locations: Minneapolis, Duluth and Ely, Minnesota, representing urban, light industrial, and pristine area type of aerosols, respectively. PM2.5 averages from Minneapolis and Duluth compare well with three-year averages from state regulatory sampling. Copyright 2014 American Association for Aerosol Research

A novel quartz crystal cascade impactor for real-time aerosol mass distribution measurement

ABSTRACT A quartz crystal microbalance (QCM) based instrument has been developed for real-time aerosol mass distribution measurement. It includes two key components: a six-stage QCM micro-orifice cascade impactor and a novel relative humidity (RH) conditioner. This instrument operates at a flow rate of 10 L·min−1 and measures the mass of the collected particles in six aerodynamic diameter channels between 45 nm and 2.5 μm. The RH conditioner ensures that the aerosol particles are collected at an RH between 40% and 65%, which is critical for eliminating particle bounce and for ensuring optimal particle coupling with the QCM. The nozzles of the impactors are clustered in the center of the nozzle plates. Therefore, particles are deposited on the central electrode of the QCM, where the mass calculated from first principles (i.e., Sauerbrey equation) agrees with the actual collected mass. The QCM response is linear up to around 130 μg for solid particles and up to around 2 μg for liquid particles. The collection efficiency curves of the QCM impactor stages were measured experimentally with monodisperse aerosols, and the results agree with the predictions of established impactor theory. This QCM-based instrument has also been tested with ambient aerosols with varying temperature and relative humidity. The aerosol distributions measured by this new instrument are in good agreement with simultaneous independent measurements carried out with a wide-range particle spectrometer (MSP Model 1000XP WPS). Copyright

Generation of monodisperse aerosols by combining aerodynamic flow-focusing and mechanical perturbation

ABSTRACT A novel instrument has been developed for generating highly monodisperse aerosol particles with a geometrical standard deviation of 1.05 or less. This aerosol generator applies a periodic mechanical excitation to a micro-liquid jet obtained by aerodynamic flow-focusing. The jet diameter and its fastest growth wavelength have been optimized as a function of the flow-focusing pressure drop and the liquid flow rate. The monodisperse aerosol generated by this instrument is also charge neutralized with bipolar ions produced by a non-radioactive, corona discharge device. Monodisperse droplet generation in the 15- to 72-μm diameter range from a single 100-micron nozzle has been demonstrated. Both liquid and solid monodisperse particles can be generated from 0.7- to 15-μm diameter by varying solution concentration, liquid flow rate, and excitation frequency. The calculated monodisperse particle diameter agrees well with independent measurements. The operation of this new monodisperse aerosol generator is stable and reliable without nozzle clogging, typical of other aerosol generators at the lower end of the operating particle size ranges. Copyright