Electric Sensing Zone

Electric Sensing Zone, also referred to as the Coulter Technique or Coulter Counter, is a true high-resolution particle counter and size distribution analyzer. Samples are analyzed in a conductive fluid and drawn through a precision aperture. A platinum electrode is placed on either side of the aperture. A vacuum is applied which draws the suspension containing particles through the aperture.  A constant voltage is applied across the aperture and any change in resistivity caused by a particle passing through it is recorded as a single particle count.

The change in resistivity is proportional to the volume of the particle, allowing for determination of the envelope volume of the particle.  A histogram of sizes is created particle by particle which attributes to the technique’s high resolution.

This technique is recognized by numerous standards and guidance agencies include ISO and USP and makes a good choice for particle size applications requiring sensitivity to outlier particles in narrow monomodal populations.   Samples analyzed frequently by Electric Sensing Zone are classified industrial abrasives such as diamonds, polymer and borosilicate microspheres, diatomaceous earth and various resin beads used in separation or treatment columns.

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  • Not sensitive to color, refractive index, density, or conductivity
  • Suitable for analyzing samples with mixed optical properties, densities and shapes
  • Suitable for irregularly shaped (e.g. elongated or needle like) particles
  • Low sample quantities are suitable for analysis


  • Multiple analyses with several tubes may be conducted and combined to capture the entire distribution of a heterogenous population
  • Carrier medium is typically an aqueous electrolyte solution such as isotonic saline
  • Porous samples not recommended as they require additional supportive analyses for accurate results

Sample Requirements

Ideal sample amount is 1 to 2 grams; as little as 200 mg may be sufficient.

For concentrated liquid samples, approximately 20 mL is required. If nearly transparent in appearance, closer to 100 mL may be required.

The above sample quantities are preferred. If sample availability is further limited, please contact us. Smaller sample quantities may be accommodated depending on sample properties, dispersion technique and required instrument.

Detection Range

Covers a nominal span of about 1.0 µm to 260 µm.

Data Reported

A comprehensive summary including particle size distribution histograms on both a number and volume-weighted basis is provided as well as the most commonly requested distribution statistics (means, 10th, 50th, 90th percentiles, etc.). Concentration can be performed and reported upon request if prior to initiation of the project.


Particle Technology Labs has the Beckman Coulter Multisizer 4e available for Electric Sensing Zone testing.

Beckman Coulter Multisizer 4e

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