A NEW RAPID AND SENSITIVE METHOD FOR THE FLUORIMETRIC DETERMINATION OF CATIONIC SURFACTANTS BY FLOW-INJECTION

ABSTRACT

A new rapid and sensitive flow-injection fluorimetric method for the determination of cationic surfactants (CS) is proposed. The determination mechanism is based on the enhancement of fluorescence intensity of the Europium (Eu³⁺)-Thenoyltrifluoroacetone (TTA) binary complex which reacts with cationic surfactants to form an ion-association complex. This complex emits a strong characteristic fluorescence at 612 nm after excitation at 345 nm. The effects of analytical and FIA variables on the determination of CS are studied and in detail especially for cetyltrimethylammonium bromide (CTAB). Under optimum conditions the working range for this example is linear from 0.05 to 15 mg L⁻¹ with a high correlation coefficient and a sample throughput of 120 samples h⁻¹ at room temperature. The relative standard deviations for 10 replicates of analysis of 10.0, 1.0, and 0.2 mg L⁻¹ CTAB are 0.2, 1.2, and 2.5%, respectively. In addition the result of FIA and batch experiments is compared, the composition of the ion-association complex is determined and the mechanism of fluorescence enhancement in the presence of CTAB is discussed. An automatic standard addition method has been designed and applied to the measurement of synthetic samples with good results.

Keywords:

• Flow-injection analysis
• Fluorimetry
• Cationic surfactants

ACKNOWLEDGMENT

The authors gratefully thank the DAAD (Deutscher Akademischer Austauschdienst) for financial support of this work.