Page 11 - Shimadzu IG-1000 Plus

The Principle Behind the Clarity

What Is the "Induced Grating Method"? Diffraction Grating Consisting of Microscopic Particles Formed by Dielectrophoresis

An alternating voltage is applied to cyclically arranged electrodes, and a cyclic concentration distribution of microscopic particles is
A periodic concentration distribution of particles formed in a medium by an external force functions as a diffraction grating. When the formed in the liquid by dielectrophoresis. Although the cyclic concentration distribution of microscopic particles acts as a diffraction
external force is removed, the particles spread out and the diffraction grating disappears. The IG method measures the decay of the grating (a particle concentration diffraction grating), if the alternating voltage is stopped, the grating diffuses and disappears
particle density diffraction grating through changes in intensity of the diffracted light, and determines the diffusion coefficient.
(patent pending).

Dielectrophoresis Optical
detector
ON

Electrode tip

Diffracted light Diffracted light
created by particles created by electrodes
Batch cell
Condensing lens
Semiconductor laser
Optical detector

Dielectrophoresis
Optical
OFF detector

Key Point of IG Method
Dielectrophoresis Dielectrophoresis
ON OFF -Precision Measurement Achieved with Modification of Electrode Configuration-
The cyclically arranged electrodes also function as a diffraction grating. The diffracted light created by
Intensity of this electrode diffraction grating is weaker than the diffracted light created by the particle concentra-
diffracted light
tion diffraction grating. In order to precisely measure the changes in the primary diffracted light
resulting from the diffusion of the particle concentration diffraction grating, it is essential that the
Large particles: Diffusion is slow
positions of the two forms of primary diffracted light do not coincide. For this reason, the electrode
Small particles: Diffusion is fast configuration has been modified as shown in the figure so that the pitch of the electrode diffraction
grating is half that of the particle concentration diffraction grating (Patent No.4270070).
Time
Variation in Intensity of Diffracted Light over Time
IG-1000 Plus
10 Single Nano Particle Size Analyzer 11