What substrate is used in a chromogenic factor assay?

In a chromogenic factor assay, the substrate used is p-nitroaniline. This assay is designed to measure specific coagulation factors in the blood by using a substrate that, when cleaved by the enzyme activity of the target factor, releases p-nitroaniline. The amount of p-nitroaniline produced is directly proportional to the activity of the coagulation factor being assessed.

When the chromogenic substrate is cleaved, the resulting increase in the concentration of p-nitroaniline can be quantified through spectrophotometric methods, allowing for precise measurement of factor activity. This technique is particularly valuable because it provides a clear, colorimetric readout that can be easily analyzed.

Other substances mentioned do not serve as substrates in this specific context. Chlorophenol red, for example, is typically used in acid-base indicators rather than in coagulation assays. Prussian blue is a compound related to iron and does not participate in chromogenic assays. Ferricyanide, while involved in various chemical reactions, does not have a role in the specific detection of coagulation factors in chromogenic assays. Therefore, p-nitroaniline is uniquely suited for this purpose, making it the correct choice.