Supercritical fluid extraction using supercritical carbon dioxide was applied to extract nitroaromatic compounds covering a wide range of polarity from soils having high humic organic matter content. Commercially available non-ionic, anionic and cationic surfactants were utilised as modifiers to enhance analyte solubility in the fluid.

The applied surfactants turned out to have no significant beneficial impact on target analyte recoveries. On the contrary, surfactants exercise a detrimental effect on recovery by the formation of a “layer” on the soil or by “plugging” micropores, thus hampering analyte desorption. The surfactant deposition onto the soil under supercritical conditions was traced using electrospray ionisation mass spectrometry. The surfactant can be fully solubilised by adding polar methanol modifier to the fluid, but there was no synergetic effect between surfactant and modifier.