Which gas detection method involves chemical analysis?

The method that involves chemical analysis to detect gases is through the use of an oxygen indicator. This method typically employs chemical reactions to quantify the amount of oxygen in a given sample. Specifically, oxygen indicators are designed to react with oxygen to produce a measurable change, often in color or fluorescence, which can then be analyzed to determine oxygen levels.

In contrast, the other methods such as nitrogen testing, methane detection, and carbon dioxide testing may involve different detection techniques, such as infrared spectroscopy, catalytic bead sensors, or other physical sensing mechanisms that do not require chemical analysis in the same way that oxygen indicators do. These methods are more focused on detecting the presence or concentration of gases rather than employing a chemical reaction to measure them directly.