Which sampling method is preferred for analyzing volatile compounds in water?

Passive sampling is the preferred method for analyzing volatile compounds in water due to its ability to collect samples over an extended period without the need for active intervention. This method utilizes sorptive materials that allow volatile compounds to partition from the water into the sampler, providing a more representative concentration of these compounds over time.

Given that volatile compounds can evaporate quickly when exposed to the atmosphere, passive sampling minimizes the risk of loss through volatilization that can occur with more traditional sampling techniques like grab sampling. Passive methods typically operate without the disturbances that can alter the sample's concentration, ensuring that the data reflects more accurately the ambient conditions of the water.

In contrast, grab sampling involves collecting a single sample at a specific time, which may not capture variations in concentration that occur throughout the day. Composite sampling combines multiple samples but may still face challenges with the volatility of compounds. Continuous sampling, while providing ongoing data, may not be ideal for all volatile compounds since it can also lead to loss of analytes during transport and storage. Thus, passive sampling stands out as a method that effectively balances these challenges.