A gas chromatograph is an analytical instrument used to separate and analyze compounds in a gas mixture. It works by vaporizing a sample and passing it through a column filled with a stationary phase. Different components of the mixture travel at different speeds, allowing them to be separated and detected. The results are displayed as a chromatogram, which shows the time it takes for each component to pass through the column. This information helps identify and quantify substances in various fields, including chemistry, environmental monitoring, and forensic science.