Inter-laboratory comparison of liquid chromatographic techniques and enzyme-linked immunosorbent assay for the determination of surfactants in wastewaters

Seven laboratories participated in an inter-laboratory comparison exercise within the framework of the PRISTINE, SANDRINE and INEXsPORT European Union Projects. Solid-phase extraction (SPE) methodologies were used for the ext raction of target analytes from wastewaters. The analytical strategies were based on liquid chromatography (LC) coupled to mass spectrometric (MS) or to fluorescent (FL) detection in all cases with the exception of one labora tory using a test-tube enzyme-linked immunosorbent assay kit. Samples were spiked with the surfactants nonylphenolpolyglycol ether, coconut diethanola mide, linear alkylbenzene sulfonate, nonylphenolpolyglycol ether sulfate, a lkylpolyglycol ether and secondary alkane sulfonate. After enrichment on pr eviously conditioned SPE cartridges, the SPE cartridges were distributed am ong the participating laboratories without the information about the amount of spiked surfactants. in addition, SPE cartridges loaded with a real-worl d environmental sample containing a tannery wastewater were also analyzed. The results of the programme showed that SPE followed by LC-MS techniques a re reliable for the surfactants determination at submicrogram to microgram per liter levels in wastewaters. Inter-laboratory precision values were cal culated as the reproducibility relative standard deviation (RSDR) which was determined from the reproducibility standard deviation (s(R)) and the aver age concentration at a particular concentration level. When data from all l aboratories were pooled, the RSDR values ranged from 5.1 to 28.3% for the d etermination of target analytes. The most accurate result corresponded to t hat given for linear alkylbenzene sulfonates. Taking into account that diff erent methodologies were used (including non-chromatographic techniques) an d the complexity of the samples analyzed, it can be considered that accepta ble reproducibility values were obtained in this inter-laboratory study. (C ) 2000 Elsevier Science B.V. All rights reserved.