FLOW-INJECTION METHOD FOR THE DETERMINATION OF ANIONIC SURFACTANTS AFTER LIQUID-LIQUID-EXTRACTION USING ON-TUBE VISIBLE ABSORPTION AND FLUORESCENCE DETECTION

Anionic surfactants in water samples were determined by a spectrophotometric and a spectrofluorimetric method involving flow injection coupled with liquid-liquid extraction. On-tube detection without any phase separators was adopted by using a glass capillary flow cell (inner diameter 0.8 mm). Two kinds of dyes were examined: cationic dyes, such as Methylene Blue and Ethyl Violet, and neutral dyes, such as Rhodamine B and 4-(4-dimethylaminophenylazo)-2-methylquinoline. The latter dyes were found to be advantageous and were dissolved in an organic phase as an electrically neutral species. They combined with anionic surfactants in the presence of protons, and changed their colour and/or fluorescence intensity. By using the second group of reagents, anionic surfactants could be determined with low background noise.