Surface enhanced infra-red spectroscopy with modified silver nanoparticles (AgNPs) for detection of quaternary ammonium cationic surfactants

A novel surface enhanced infra-red spectroscopy (SEIRS) method with silver nanoparticles (AgNPs) assisted by single drop microextraction (SDME) was developed for detection of total mixed quaternary ammonium cationic surfactants (QACS) in water samples. SDME was used to separate and preconcentrate QACS from water samples into an organic solvent containing citrate-capped AgNPs through the electrostatic and hydrophobic interactions, and we abbreviated this as the AgNP-SDME/SEIRS method. Here, the AgNPs served to enhance the signal intensity of QACS through the aggregation of NPs, which resulted in an increase in the hot-spot density for effective absorption of IR radiation. The linearity range obtained for determination of total mixed QACS in water samples was 1-20 g L-1 with a limit of detection (LOD) and limit of quantification (LOQ) of 0.03 g L-1 and 2.0 g L-1, respectively. The excellent recovery percentage (95.4-109.7%) in domestic wastewater samples showed that the method is found to be selective for the determination of total mixed QACS in complex sample matrices. The advantages of using AgNP-SDME/SEIRS are its simplicity, selectivity and sensitivity towards the analysis of total mixed QACS in various domestic effluent samples.