Quaternary ammonium surfactants (QAS) are one of the most important surfactants in industry

pharmaceuticals and cosmeticsTheir rapid detection and accurate quantification plays a key role in controlling their application or existence in the environmentIn the present study

a novel method was established to detect the critical micelle concentration (CMC) of QAS in water and to quantify the surfactant concentration below its CMC

based on the fluorospectrum and fluorescence intensity change of fluorescein isothiocycanate (FITC)This approach was simple and sensitive

achieving the limit of detection (LOD) of dodecyltrimethylammonium bromide (DTAB) and cetyltrimethylammonium bromide (CTAB) at 0.11 mmol·L-1 and 1.7 μmol·L-1

respectivelyAnd the quantification range of DTAB and CTAB was 0.11—9.73 mmol·L-1(0.034—3.0 g·L-1) and 1.7 μmol·L-1—0.27 mmol·L-1(6.2×10-4—0.1 g·L-1)

respectivelyThe CMCs were detected as 12—13 mmol·L-1(DTAB) and 0.70—0.96 mmol·L-1(CTAB)

which were consistent with the results measured by the conductance

surface tension of the solution or by the pyrene probeConcentration characterization of the QASwater solution by FITC has provided a new

safe

simple and accurate approach to analyzing and monitoring the surfactants in the environment or in their wide application.