Which type of samples must be collected without any air in them?

The requirement for certain types of water samples to be collected without any air is primarily related to the preservation of the integrity of the samples for subsequent analysis. Specifically, when dealing with TTHM (Total Trihalomethanes), HAA5 (Haloacetic Acids), VOCs (Volatile Organic Compounds), and SOCs (Synthetic Organic Compounds), the presence of air can lead to the oxidation of these compounds, altering their chemical composition and potentially leading to inaccurate results during analysis.

For TTHMs and HAA5s, which are by-products of chlorination in drinking water, exposure to air can lead to their dissipation, as these compounds can volatilize. Similarly, VOCs are particularly sensitive to changes in concentration due to their volatile nature, meaning that any air trapped in the sample can result in losses of these compounds before laboratory analysis. Therefore, it is critical that samples collected for these analyses are preserved without any headspace to ensure that they accurately represent the water quality at the time of sampling.

In contrast, biological samples, turbidity samples, and contaminated water samples may not have the same stringent requirements regarding air exposure, making the proper collection methods for TTHM, HAA5, VOC, and SOC samples