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In its classical implementation, the electrical resistance measurement (ERM) method of particle sizing and particle counting relies on an increase in the electrical resistance of a sensing zone filled with conductive fluid, that is caused by the presence of a nonconductive particle in that zone. In the first approximation, that increase is caused by the displacement of a volume of the fluid by the particle, which reduces the number of ions in the sensing zone.
However, as shown by Zhang Z et al 2005, the net change in the sensing zone resistance is also affected by an electric charge carried by the particle. In fact, if the particle adds more charge to the sensing zone than it removes by displacing the conductive fluid, the sensing zone resistance may decrease. The effect of the particle-carried charge is more significant for the weakly conductive fluids. Thus, the two factors: (1) the displacement of the conductive fluid ions by the particle and (2) introduction of its own charge by the particle affect the sensing zone resistance in competing ways. Chang H et al 2004 reported a similar phenomenon caused by a passage of a negatively-charged DNA molecule through a nanopore with a diameter of 50 nm.
The magnitude of a charge carried by a particle depends on the particle type, hence the ERM method can be used to discriminate various particle types when the fluid conductance is optimized. Specifically, Jagtani AV et al 2006 and Zhang Z et al 2005 show that, with the conductive fluid being a 0.01 M aqueous solution of KCl, some tree and grass pollen particles (diameter of 17 to 25 µm) can be differentiated from latex particles (diameter of 20 to 40 µm) by using an aperture with a diameter of ~100 µm. Pollen particles examined by Jagtani et al and by Zhang et al all caused the sensing zone resistance to decrease, albeit various types of pollen particles produced different resistance decreases. These authors attributed the decrease to charges carried by those particles. In contrast, latex particles caused the sensing zone resistance to decrease.
| CITATION: Jonasz M. 2006. ERM particle sizing/counting method detects particle charge (www.tpdsci.com/Tpc/ERMCharge.php). In: Top. Part. Disp. Sci. (www.tpdsci.com). |
HISTORY: Published: 22-Feb-2006 Modified: 19-Jan-2007 Peer-reviewed: 16-May-2006 |
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