The procedures to implement a chromatographic method for the quantification of linear alkyl benzene sulfonate (LAS) in the influent, effluent and sludge of a wastewater treatment plant (WWTP), and in river water and sediment, are described and evaluated. The columns octylsilane (C8) and octadecylsilane (C18) for high performance liquid chromatography were evaluated for separation of LAS homologues. The results showed that both columns separated the four homologues, but C18 was better for separation of the isomers of each homologue. This enabled to qualitatively evaluate the degradation of homologues in the WWTP, according to their respective isomers. Samples pre-treatment by solid phase extraction (SPE) columns, strong anionic exchange (SAX) and C18, was also evaluated. SPE was necessary for water river samples, either to concentrate LAS or to remove interference in the matrix; however, for WWTP samples, SPE showed unnecessary. The recovery of LAS homologues, after the procedures for sample preparation, was 90 to 110% with an accuracy of 1 to 5%. The WWTP was efficient in LAS removal from domestic sewage; however, the concentrations in water and sediments of the receiving body were higher than the limits established by legislation due to illegal discharges of untreated sewage.
Keywords:
LAS homologues and isomers; anaerobic treatment; validation of chromatographic method; SPE pre-treatment
