1. Scope

This guide deals with the measurement of mobility and zeta potential in systems containing biological material such as proteins, DNA, liposomes and other similar organic materials that possess particle sizes in the nanometer scale (<100 nm).

2. Referenced Documents

1- ASTM Standards: E1470 Test Method for Characterization of Proteins by Electrophoretic Mobility (Withdrawn 2014) E2456 Terminology Relating to Nanotechnology

2- ISO Standards: ISO 13099-1 Colloidal Systems — Methods for ZetaPotential Determination — Part 1: Electroacoustic and Electrokinetic Phenomena

3- ISO 13099-2 Colloidal Systems — Methods for ZetaPotential Determination — Part 2: Optical Methods

4- ISO 13321 Particle Size Analysis — Photon Correlation Spectroscopy

3. Terminology

3.1 Definitions—Definitions of nanotechnology terms can be found in Terminology E2456.

3.2 Definitions of Terms Specific to This Standard: 3.2.1 Brownian motion, n—is the random movement of particles suspended in a fluid caused by external bombardment by dispersant atoms or molecules.

3.2.2 dielectric constant, n—the relative permittivity of a material for a frequency of zero is known as its dielectric constant (or static relative permittivity).

3.2.2.1 Discussion—Technically, it is the ratio of the amount of electrical energy stored in a material by an applied voltage, relative to that stored in a vacuum.

3.2.3 electrophoretic mobility, n—the motion of dispersed particles relative to a fluid under the influence of an electrical field (usually considered to be uniform).

3.2.4 isoelectric point, n—point of zero electrophoretic mobility.

3.2.5 mobility—see electrophoretic mobility.

3.2.6 redox reaction, n—a chemical reaction in which atoms have their oxidation number (oxidation state) changed.

3.2.7 stability, n—the tendency for a dispersion to remain in the same form for an appropriate timescale (for example, the experiment duration; on storage at 358K).

3.2.7.1 Discussion—In certain circumstances (for example water colloid flocculation) instability may be the desired property.

3.2.8 van der Waals forces, n—in broad terms the forces between particles or molecules.

3.2.8.1 Discussion—These forces tend to be attractive in nature (because such attractions lead to reduced energy in the system) unless specific steps are undertaken to prevent this attraction.

3.2.9 zeta potential, n—the potential difference between the dispersion medium and the stationary layer of fluid attached to the dispersed particle.

3.2.10 zwitterionic, n—a molecule with a positive and a negative electrical charge.

3.2.10.1 Discussion—Amino acids are the best known examples of zwitterions.

4. Summary of Practice

4.1 Introduction—It is not the intention of this guide to spend any significant time on the theory of zeta potential and the routes by which a particle acquires charge within a system. Indeed it may be more appropriate to deal only with the movement or mobility of particles under an electrical field where conversion to zeta potential is not even attempted. The relevant text books (for example, see Hunter) should be consulted along with the more academic ISO references (ISO 13099-1 and ISO 13099-2). The IUAPC report is also very useful, albeit fairly theoretical, but it does contain a section (4.1.2) entitled ‘How and under which conditions the electrophoretic mobility can be converted into ζ-potential’. The Corbett and Jack paper contains excellent practical advice for measurement of protein mobility and is recommended.

4.2 Test Method E1470 is based around a sole vendor’s equipment, but this does not deal with the basis of the measurement or provide guidance in the practice of the measurement. It is one intention of this guide to address those deficits.

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