Potential of coacervation processes for the extraction of amphiphiles (linear alkyl benzenesulphonates) from sewage sludge samples prior to liquid chromatography

A new approach was developed for the monitoring of linear alkyl (C10–C13) benzenesulphonates (LASs) in sewage sludge. It was based on their extraction with the anionic surfactant sodium dodecanesulphonate (SDoS) that undergoes coacervation under acid conditions. The target compounds formed mixed aggregates with SDoS by ideal hydrophobic interactions which made possible the breakdown of LAS–sludge interactions and provided high extraction yields. Variables affecting extraction were optimised using a fortified dehydrated sludge. Recoveries for LASs were found independent on the length of alkyl chain. Liquid chromatography–fluorimetry was used for separation and detection of LAS homologues. Detection limit for LAS in the sludge was 5 mg/kg. Concentration levels of total LASs in activated and dehydrated sludge collected from two different sewage treatment plants were in the range 0.26–0.56 g/kg with LAS homologues ranging from 29 to 223 mg/kg. The method did not require clean-up or preconcentration steps.