Spot analysis

Spot analysis, also called a spot test or spot test analysis, is a simple chemical technique that uses just a drop or two of a chemical solution, typically applied to a large piece of filter paper, with no need for complex instruments. Its development and widespread use are credited to Fritz Feigl. The term also describes a common test in microbiology.

In chemistry, Feigl’s work built on earlier research by Hugo Schiff—who published the first known spot test in 1859 for detecting uric acid—and on capillary analysis by Christian Friedrich Schönbein and Friedrich Goppelsröder. In 1952, the Chemical Society of Midland held a symposium for Feigl’s 70th birthday, drawing 500 scientists from 24 countries, where all main sessions focused on spot tests. The method relies on the visible colors of compounds to indicate chemical reactions, and it has since been adapted for modern quantitative techniques.

In microbiology, a spot assay or spot test checks the growth rate of bacteria or yeast on different media or performs serial dilutions of microbes. A 96-pinner, sometimes called a frogger, is often used for these tests. Spot assays also appear in high-throughput screening, such as monitoring the growth of mated cells or detecting protein-protein interactions in a yeast two-hybrid test, frequently with robotic assistance.