1.1 ,This test method covers the determination of (Tri-n-butyl)-n-tetradecylphosphonium chloride (TTPC) in water by dilution with acetone, filtration and analysis by liquid chromatography/tandem mass spectrometry. This test method is not amenable for the analysis of isomeric mixtures of Tributyl-tetradecylphosphonium chloride. TTPC is a biocide that strongly adsorbs to soils.2 The water samples are prepared in a solution of 75 % acetone and 25 % water because TTPC has an affinity for surfaces and particles. The reporting range for this method is from 100–,4000 ng/L. This analyte is qualitatively and quantitatively determined by this method. This test method adheres to multiple reaction monitoring (MRM) mass spectrometry.