Cationic surfactants Dragendorff reagent

The bismuth active substances (BiAS) method for the determination of nonionic surfactants with barium tetraiodobismuthate (BaBil4, modified Dragendorff reagent) is used in the standardized (DIN-Norm) procedure in Germany, as well as in other countries. Ba as a hard Lewis acid forms cationic coordination complexes with the polyethoxylate chain of the nonionic surfactants, which are precipitated by [Bim in the presence of acetic acid. The orange precipitate is then dissolved with ammonium tartrate solution, and the released bismuth ions are determined by potentiometric titration with pyrrolidinedithiocarbamate solution. Waters et al. optimized the BiAS procedure by introduction of a cation/anion exchange clean-up of the sublation extracts. The BiAS procedure fails to determine ethoxylates with less than five ethoxy units because these compounds are not precipitated by barium tetraiodobismuthate. Thus, this procedure is not suitable for determination of APEO metabolites, i.e., the shorter APEO and AP. ... 

Block distinguished between classes of surfactants using two TLC systems (8). The first used Silica Gel G F-254 with 90 10 ethanol/acetic acid. For visualization, the upper part of the plate was sprayed with pinacryptol yellow to detect anionic surfactants and soap, while the lower portion was sprayed with Dragendorff reagent to detect nonionics and cationics. For further separation of nonionics and cationics, a Silica Gel G plate was used with 80 19 1 methanol/chlorofoim/0.05 M sulfinic acid. Detection was by spraying with palatine blue solution. For exact characterization, the spots were removed, eluted with solvent, and the surfactants identified by IR spectroscopy. 

Apply spots of 1-10 pg cationic surfactant to a Silica Gel 60 plate, applying standards at the same time. Condition plates for 20 min at 37% relative humidity and develop with ethyl acetate/acetic acid/water, 4 3 3. Dry at room temperature until the odor of acetic acid is gone. Spray with Dragendorff reagent. Dry in subdued light with a stream of air until the odor of acetic acid is again absent. Cover with glass, and measure on a densitometer by transmission at 525 nm. 

Hellmann, H., Application of modified Dragendorff reagent to the determination of cationic surfactants in the aquatic environment (in German), Fresenius Z. Anal. Chem., 1989, 335, 265-271. 

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