Interlaboratory trial on the analysis of individual isomers of nonylphenol in water samples according to ISO 24293: 2009

Abstract

ISO 24293: 2009 describes a new international standard method for the determination of 13 individual 4-nonylphenol (4-NP) isomers in non-filtered samples of drinking water, wastewater, ground water and surface water using solid-phase extraction and gas chromatography/mass spectrometry. To validate this method, 17 laboratories from 3 different countries participated in an interlaboratory trial to determine its performance characteristics. The interlaboratory trial was evaluated according to ISO 5725-2, and included four triplicate non-filtered water samples: surface river water with low (RW1) and high (RW2) concentrations of 4-NP standard spiking and wastewater with low (WW3) and high (WW4) concentrations of 4-NP standard spiking. The repeatability variation coefficients (within-laboratory precision) varied for all isomers, ranging from 4.4% to 21.6%. The reproducibility variation coefficients (between-laboratory precision) were found to be 24.9 ± 6.4% for RW1, 30.6 ±10.7% for RW2, 63.3 ± 34.6% for WW3, and 36.6 ±13.5% for WW4. Proficiency testing concerning the ability of analytical laboratories was performed based on ISO/IEC Guide 43-1, "Proficiency testing by interlaboratory comparisons". The laboratories were evaluated using z scores based on a robust method; 8 to 13 laboratories (71% to 92%) were estimated to be "satisfactory (| z | ≦2)", 0 to 1 laboratories (0% to 10%) as "questionable (2 <3)", 1 to 3 laboratories (7.7% to 23%) as "unsatisfactory (| z | ≧3)" for all water samples tested. © 2010 The Japan Society for Analytical Chemistry.