Particle sensing-zone technique

Sensing-zone techniques have been applied to oil-in-water emulsions, although they cannot distinguish between dispersed droplets and solid particles [66], Unless an emulsion sample contains no particles, or is very well characterized, the results... 

Figure 2.9 Illustration of a sensing-zone technique. As the suspended particle or droplet passes through the sensing zone, the capacitance or resistance changes in proportion to the size of the particle. These signals can be sorted and interpreted as a size distribution in terms of equivalent spherical diameters.

A particle or droplet-sizing technique in which the flow of dispersed species in a capillary, between charged electrodes, causes changes in conductivity that are interpreted in terms of the sizes of the species. Coulter is the brand name for the automated counter. See also Sensing Zone Technique. 

II ASTM E 1772-95(1995) (1997), Particle size distribution of chromatography media by electrical sensing zone technique, 450... 

Sensing Zone Technique A general term used to refer to any of the particle- or droplet-sizing techniques that rely on (usually) conductivity or capacitance changes in sample introduced between charged electrodes. Also termed resistazone counter. An example is the Coulter counter. Sensing zone technique is also used with reference to similar... 

Multiple techniques can be used to measure the particle size distribution, for example electrozone sensing, sedimentation, laser diffraction, and microscopy. With the exception of microscopy, they all require calibration and the results depend on the technique. For example, in a round-robin study reported in Reference 4, the commonly used electrical sensing zone technique (Coulter Counter) was compared to microscopy and sedimentation. The average particle size determined by the electrical sensing zone method was by about 25%... 

Number concentrations can be determined by sensing zone techniques (see Section 2.4.2), which provide an overall average number concentration. A condensation particle counter (CPC) can provide number concentrations for solid aerosols having particle sizes as small as a few nanometres in diameter [129]. In such an instrument, the aerosol is saturated with a vapour (usually water or an alcohol) and then taken to conditions of supersaturation. Vapour condensation on the particles produces droplets having diameters in the range 5-15 pm [124]... 

Besides for particle sizing, the optical sensing technique can also be employed for measurement of the particle number concentration. Discussions mentioned earlier regarding the measurement errors for the resistivity sensing zone technique apply here as well. When more than one particle is present in the sensing zone, error can occur. 

If the particle size distributions are characterized by the average diameters at the cumulative masses of 10, 50, and 90%, the data scattering measured by different techniques can be represented by the diameter ratios at the cumulative masses of 10, 50, and 90%, or DRio, DR50, and DR90. Since the particle diameter measured by the electrical sensing zone technique is to be the equivalent volume diameter and is independent of the particle shape, its particle diameter is defined to be one. The particle diameters measured by other techniques are then ratioed with this diameter. The experimental results of DRjo, DR50, and DR90 are summarized in Table 5. It can be seen that the results of particle analysis from different techniques can be quite different. 

One question which then arises is, What do the various particle analyzers measure From the electrical sensing zone technique, we get a number distribution, in spite of the fact that the method measures the volume of the individual particles. Prom the particle volume the instrument computes a volume equivalent particle diameter (see Chap. 2). The instrument then counts and reports the particles within a series of narrow (volume equivalent) diameter ranges. 

Photozone Counter A particle- or droplet-sizing technique, analogous to the electrical sensing-zone methods, that relies on visible light absorption in sample introduced into a small chamber. The particles or... 

Care must be taken in selecting an indirect method since these require assumptions about either the real size distribution, the shape, or the process on which the analysis is based. For example, conductometric sensing zone equipment relies on the assumption of sphericity, which is usually reasonable for emulsion droplets, but often is not reasonable for particles in a suspension. Similarly, light-scattering techniques are reliable only if the particle shape and refractive index are known or assumed, and adsorption analyses rely on model adsorption isotherms, the uniformity of particle size and porosity, and the orientation of adsorbed species. Each technique has its own limitations. For example, concentrated dispersions... 

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