Optimization and validation of a new method for analysis of linear alkylbenzene sulfonates in sewage sludge by liquid chromatography after microwave-assisted extraction.

A new approach has been developed for the monitoring of linear alkylbenzene sulfonates (LAS) (C10-C13) in sewage sludge. It is based on microwave-assisted extraction (MAE) prior to high performance liquid chromatography coupled with diode array (HPLC-DAD) and fluorescence (HPLC-FL) detectors. Column Zorbax XDB-C8, 150 mm x 4.6 mm i.d., 5 microm particle size was used as well as acetonitrile-water containing 0.1 M NaClO4 (65:35) and isocratic elution. Compounds were isocratically eluted over 6 min runtime at a flow rate of 1 mL min(-1). Since polar interferences are eluted between 0 and 2 min, they do not interfere in the analysis. The column was thermostated at a temperature of 25 degrees C. For the determination of LAS, DAD-UV (lambda(ex) = 225 nm) and fluorescence (lambda(ex) = 225 nm, lambda(em) = 295 nm) detectors were employed. The main factors affecting the extraction efficiency (extractant volume, microwave power and irradiation time) were optimized using a compost sludge. The detection limit for total LAS in the sludge was < 5 mg kg(-1). The extraction of C10-C13 homologues is carried out by using an extraction time of 10 min and 5 mL of methanol; whereas Soxhlet needs a 12 h extraction. The method did not require clean-up or preconcentration steps. Concentration levels of LAS were between 13,037 mg kg(-1) for digested sludge and 2492 mg kg(-1) for compost sludge.