Particle counters, types

FIGURE 11.62 Experimental calibration curves for a commercial single-particle counter and two types of calibration aerosols dioctyl phthalate (DOP) and coal dust (adapted from Whitby and Willeke, 1979). 

Multiple Ratio-Type Single-Particle Counters (MRSPC). Diagnostic techniques using the light scattered by an individual particle passing... 

Ideally a single-particle counter should have a response function monotonically dependent on particle size exemplified by that portion of Figure I for n = 1.57 — 0.56i and a < 17 but with zero response for all other a. The real situation however is quite different as indicated. Two types of deviations from desired behavior can be identified. 

The Coulter principle is also standard for dry toners [8,9] and an accepted method for aluminum oxide powder [10], chromatography media [11], polymeric powders [12], plutonium [13], filter evaluation [14], catalytic material [15] and comparing particle size distribution using alternative types of particle counters [16]. In ASTM method C-21 it states that the experience of several laboratories indicates that the method is capable of a repeatability of 1% and a reproducibility of 3% at the 95% confidence level. Operating procedures for this technique are also covered in BS3405 [17]. The method is also the subject of an international standard [18]. 

In this section, we briefly review three types of instruments, the optical particle counter, electrical aerosol classifier, and diffusion battery. These system.s are based on very dilTerent physical characteristics of the aerosols. The optical counters respond to signals from individual particles. The electrical analyzers depend on the measurement of a current carried by a slreaJTi of cbrnged aerosol particles. The ditfusion battery also depends on the behavior of particle clouds. The system often used to cover the size range from about 10 nm to 10 /jm is a combination of (a) the electrical analyzer up to about 0.2 jum and (b) the optical particle counter over the rest of the range. 

The number-size distribution of ambient particles was monitored by an optical particle counter (OPC) (RION, KC-OID). Information concerning the accuracy of the OPC s size determination was checked by the manufacmrer (RION). The four-step known size monodisperse polystyrene type latex (PSL) spheres (0.294, 0.505, 1.001, and 2.106 pm) were employed. The OPC sizing accuracy check was conducted by sampling of these PSL particles. In the field measurement, OPC was operated at intervals of every 30 min. The flow rate for the OPC was 3 X 10 m h During the sampling period, the ranges of temperature and relative humidity (RH) were 12.8-28.4 °C and 30-79%, respectively. 

CCN number concentration is measured using a CCN counter (CCNC). Several types of CCNCs have been developed (McMurry, 2000 Nenes et al., 2001 Roberts and Nenes, 2005). In most CCNCs, supersaturated conditions are produced by creating a temperature difference on wetted walls. CCN-active particles grow to large droplets in the artificial supersaturated environment. The number of droplets is then counted using an optical particle counter (OPC) (e.g., Stratmann et al., 2004 Roberts and Nenes, 2005) or a charge coupled device (CCD) camera (Otto et al., 2002). The most important parameter in CCN measurement is the precise value of the supersaturation (S) inside the instrument, which ensures compatibility with other studies (Seinfeld and Pan-dis, 2006). 

One of the promising methods for producing satisfied quantities of a powder with narrow size distribution and nanometric mean diameter is electrospray pyrolysis method. In this method, a meniscus of a precursor (spray solution) at the end of capillary tube becomes conical when charged to a high voltage (several kilovolts) with respect to a counter electrode. The droplets are formed by continuous breakup of a jet extending from this liquid cone, known as Taylor cone. Lenggaro, Xia, Okuyama, and Fernandez de la Mora, in their papers published from 2000 to 2003, described how this technique functions and how it is possible to measure online a size distribution of particles obtained from different types of precursor systems. For this purpose, they used differential mobihty analyzer and a condensation nucleus/particle counter (CNC/ CPC) [19-26]. 

A large number of latex agglutination immunoassays have recently been adopted from clinical chemistry. These assays are based on the visualization of antigen-antibody complexes by the attachment of latex particles or gold colloids. Entities of this type with dimensions in the nanometer or micrometer range can be quantified by turbi-dimetry, nephelometry, light scattering techniques, and particle counters [22] - [25]. 

Measurement of the Aitken nuclei or Aitken particles can be made by a pneumatic expansion type particle counter. Aitken particles is the name given to those atmospheric particles whose size lies between a few angstroms (1 angstrom is 10 cm or 10 " pm) and 0.1 pm. They constitute the greatest contribution to the spectrum of sizes in the atmospheric aerosol. The measurement of the concentration of these particles is based on their ability to act as condensation nuclei for water vapour, when this is supersaturated. 

Besides detecting aerosol particles, the condensation particle counters can also be used to detect small molecular clusters of aerosol particles (Kulmala et al., 2005). When the saturation ratio is increased above a certain limit by increasing the temperature variation in a condensation particle counter, ion clusters will be activated first. Further increase of the saturation ratio will then also activate neutrally charged clusters and finally new aerosol particles are formed via homogeneous nucleation. By varying the temperature variation and the type of... 

Binding ratios of SDS (BHD Ltd.) and CPC (Tokyo Kasei Ltd.) to HPC (M.W. =11 -I5xl0 Tokyo Kasei Ltd.) were determined at 30 °C by an equilibrium dialysis method. Cloud point of an HPC solution was observed by the naked eye. Amounts of p-dimethylaminoazobenzene (Nakarai Ltd.) solubilized by the surfactant micelle and the surfactant-polymer complex were determined at 30 °C by colorimetry at 1 = 418 nm. Viscosity was measured by an Ubbelohde-type capillary viscometer, a cone-plate rotary viscometer, or a Brookfield-type rotary viscometer at 25 or 30 °C. Mean diameter of secondary particles of kaolinite in its dilute suspension (1 g/dl) was estimated by a Coulter counter (type TA-II) in 154 mmol/dm NaCl at room temperature. 

A.D.Bates Performance Limit of an Obscuration Type Particle Counter with Tungsten Source Private communication... 

In any type of particle counter, the number of particles in a metered volume of suspension will vary from the number in any other identically metered volume, as expected from statistical theory. A mean count of h particles per unit volume could be expected to vary according to the i tandard deviation of measurement, calculated as (h) . Thus a mean count of 100,000 particles can be obtained with a standard deviation of 316.2 particles, i.e. a precision (expressed as coefficient of variation, c.v.) of 0.316%. 

The second type of calibration standard is a batch ofpolydisperse particles with a known size distribution and a carefully determined concentration. For these polydisperse standards, the cumulative concentration at any selected size should not differ from the specified value by more than 10%, except for a certain population of particles that has only a few particles. This type of calibration can be carried out by incorporating data from another particle characterization technology. For example, by comparing the pulse-height distribution from an optical particle counter with the size distribution obtained using an aerod5Uiamic... 

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