What is the main principle of chromatography in water analysis?

The main principle of chromatography in water analysis revolves around the ability to separate and identify compounds based on their different chemical properties. This technique leverages the interactions between the chemical constituents of a sample and a stationary phase, often utilizing a mobile phase to move the sample through a column or along a surface. As different compounds interact with the stationary phase to varying degrees, they will travel at different rates, resulting in a distinct separation. This separation allows for the individual identification and quantification of various substances present in the water sample, making it an essential tool in environmental monitoring and analysis of water quality.

The other options, while relevant to water analysis, do not accurately capture the fundamental essence of chromatography. Evaporating and concentrating pollutants pertains more to sample preparation techniques rather than the chromatographic process itself. Measuring temperature and pH involves direct assessment of physical and chemical properties, which is not the focus of chromatography. Observing biological activity relates to microbiological assessments rather than the separation of chemical compounds, which is the primary function of chromatography in water analysis.