![]() ![]() Usually putting a drop of the neat sample in 20 mL of liquid or doing a 1:1000 dilution should be sufficient. If the sample is highly concentrated, the sample should be diluted in the liquid of choice. In highly concentrated liquid samples, the samples may appear opaque or milky-white. salts, surfactants, dispersing agents) if any were present. It is ideal to dilute the sample in the same exact liquid it was originally prepared in, using the same concentrations of additives (i.e. For further information on preparing stable suspensions from dry powders, refer to ISO standard 14887 entitled “Sample preparation – Dispersing procedures for powders in liquids.”įor liquid samples, the sample may need to be diluted. When preparing your sample, take a good look at how the sample is dispersing. Large polymers may require more than 24 hours to completely dissolve into solution. In the case of a sample that disperses quickly, the time to disperse with agitation may be only a few minutes. Experiment with different dissolution methods and time. It is for the user to figure out the dissolution time and method. If the sample is sturdy, then sonication, vortex, spinning and other methods can be used to dissolve/suspend the sample. If the sample is a protein, the solution should not be stirred too aggressively and should never be sonicated. If your sample is a dry powder, it will need to be dissolved or suspended before it can be measured. Rinsing the filter is an important step that should not be omitted. It is always a good practice to filter the aqueous diluent using a 0.1 or 0.2 micrometer filter that has been previously rinsed according to the manufacturer’s practice. In the case of aqueous diluents like KNO3 in water, filtering is needed as salts are notoriously full of dust. If the solvent is polar, then chances are that filtering will help remove dust in the solvent. These can be used as is, as any filtering and manipulation will only risk adding dust. Non-polar solvents do not usually dissolve or carry dust. If the liquid is a pure solvent like toluene, the purest solvent possible should be sourced. A concentration of 10 mM KNO3 is ideal for all concentrations of particles. We recommend the use of KNO3 for aqueous diluents. A general salt like NaCl can be used but often the chloride ions are too aggressive and may react with the particles or adsorb to their surface. The ions with opposite charge will condense around the particle, screening long distance electrostatic interactions. To screen any charge on the particles, it is a good idea to measure in water with a trace amount of salt. The size measured in DI water will usually be too big by 2 to 10 nm due to the electrostatic interaction between the particles. Particle size measurements by Dynamic Light Scattering should not be conducted in pure de-ionized (DI) water, as the electrical double layer surrounding the particles will have long distance interaction. Although there are differences, the terms suspended and dissolved will be used interchangeably in this document. The solution or suspension to be measured is the sample in the liquid. The samples to be analyzed by DLS will be prepared in the liquid. Diluents are solvent with additives, for example a 10% by weight methanol in water or a 10 mM KNO3 salt in DI water solution. ![]() The diluent may also be referred to as the liquid in DLS textbooks. Examples of solvents are toluene or water. The term solvent refers the pure solvent used to prepare the diluent.
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