## International Gold Number
The International Gold Number (IGN) is a measure of the protective ability of a material against colloidal gold. It is defined as the number of milligrams of a material required to prevent the coagulation of 10 mL of a standard gold sol. The higher the IGN, the more protective the material is.
IGN is used to evaluate the effectiveness of various materials, such as proteins, polymers, and surfactants, in preventing the aggregation of gold nanoparticles. Gold nanoparticles are widely used in a variety of applications, including electronics, catalysis, and biomedical imaging. However, they are prone to aggregation, which can reduce their effectiveness. Materials with high IGN values can help to prevent aggregation and maintain the stability of gold nanoparticles.
The IGN test is performed by adding a known amount of the test material to a gold sol and then measuring the absorbance of the solution at a wavelength of 520 nm. The absorbance is directly proportional to the amount of aggregated gold. The IGN value is calculated by determining the amount of test material required to reduce the absorbance by 50%.
IGN is a useful tool for characterizing the protective ability of materials against colloidal gold. It can be used to compare the effectiveness of different materials and to optimize the formulation of materials for use in applications involving gold nanoparticles.
### Applications of IGN
IGN has a variety of applications, including:
* Evaluating the protective ability of proteins, polymers, and surfactants against colloidal gold
* Optimizing the formulation of materials for use in applications involving gold nanoparticles
* Studying the interactions between gold nanoparticles and other materials
### Factors Affecting IGN
The IGN of a material is affected by a number of factors, including:
* The size and shape of the gold nanoparticles
* The surface charge of the gold nanoparticles
* The concentration of the gold nanoparticles
* The pH of the solution
* The presence of other ions in the solution
By understanding the factors that affect IGN, it is possible to design materials with high IGN values that can effectively prevent the aggregation of gold nanoparticles.
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