Extraction-spectrophotometric determination of cationic surfactants using ion-association with diprotic dyestuffs and quinine

SAKAI Tadao, OHNO Noriko

doi:10.2116/bunsekikagaku.32.5_302

The sensitive and selective methods reported are based on the reaction of quinine cation with diprotic dyestuffs to form a 1 : 1 complex anion extractable into organic solvents as ion-associates with bulky cationic surfactants {benzalkonium, zephiramine, and trimethylstearylammonium (TMSA⁺) } at nearly pH7. Though the extraction could not in the absence of quinine, a cationic surfactant can be successfully coextracted with dyestuffs into organic solvents but only in the presence of quinine. At nearly pH7, other amines and quaternary ammonium compounds are not extracted. Accordingly, cationic surfactants can be determined spectrophotometrically without disturbance of amines and quaternary ammonium compounds. The extracts with bromophenol blue-quinine associates at pH 6.8 had a maximum absorbance at 610nm. The calibration curves obtained were linear over the range of (0.53) × 10^-6 M {benzalkonium: (0.1771.06)μg/ml, zephiramine : (0.1851.11)μg/ml, TMSA⁺: (0.1741.04)μg/ml} in the aqueous solution. On the other hand, the absorption maximum of bromocresol green-quinine-cationic surfactant associates at pH 8.2 occured at 630 nm. The calibration graphs showed a good linear relationship over the range of (15) × 10^-6M{benzalkonium : (0.3541.77)μg/ml, zephiramine : (0.3691.85)μg/ml, TMSA⁺ : (0.3481.74)μg/ml} in aqueous solution. Coefficients of variation for the proposed methods were about 2%.

Extraction-spectrophotometric determination of cationic surfactants using ion-association with diprotic dyestuffs and quinine

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