What type of samples should not be filtered for petroleum hydrocarbon analysis?

For petroleum hydrocarbon analysis, groundwater samples should not be filtered because filtering can remove particulate matter that may be important for accurately assessing the concentration and composition of hydrocarbons present in the sample. These particulates can include hydrocarbons that are adsorbed onto the surfaces of soil and sediment particles within the groundwater. By filtering, you may inadvertently alter the sample's integrity by losing these important components, leading to a misrepresentation of the hydrocarbon concentrations.

In contrast, surface water samples may undergo filtration to remove debris and particulates for a more accurate analysis of dissolved hydrocarbons. Soil samples are typically analyzed as is, as the soil matrix is important for understanding the contamination's extent and nature. Air samples have different collection methods that do not involve filtration at the point of analysis. Each medium has specific protocols that reflect the nature of the contaminant and its interaction with the medium being tested.