Why is methylene chloride often replaced by hexane in sample preparation for analyses detected by GC electron capture detection?

The correct answer highlights the relationship between the properties of the solvents used in sample preparation and the capabilities of the gas chromatography (GC) electron capture detector (ECD). Methylene chloride, while effective as a solvent, can interfere with the detection of halogenated compounds due to its own chemical structure, which includes chlorine atoms.

ECD is particularly sensitive to electron-capturing species, such as chlorine-containing compounds, meaning that if methylene chloride is used as the solvent, it could lead to elevated baseline noise or signal interference. This can complicate the analysis and affect the accuracy of the detection for the target analytes, which often include other halogen-containing compounds.

In contrast, hexane does not contain any chlorine and is a non-polar solvent that will not interfere with the ECD, allowing for clearer detection of halogenated compounds in the sample. Therefore, using hexane as a replacement for methylene chloride in sample preparation enhances the ability to accurately detect and quantify target analytes without the interference from chlorinated solvent components.