Whats the principle of the in-line surfactants?
Anionic surfactant is associated with the intensely colored methylene blue cation to form a chloroform extractable ion-association complex; the unassociated dye has an extremely small solubility in chloroform. The methylene blue-anionic complex is partitioned into chloroform from an alkaline methylene blue solution to avoid the negative interference of proteinaceous material present in environmental samples. The chloroform phase is then back-extracted with an acidified methylene blue solution in order to remove the positive interference of those materials such as inorganic anions e.g. nitrate, chloride etc, that form methylene blue complexes of low chloroform extractability. The absorbance of the final chloroform phase is measured at 650 nm.
