Rapid and Sensitive Determination of Benzalkonium Chloride Biocide Residues in Soil Using Liquid Chromatography-Tandem Mass Spectrometry after Ultrasonically Assisted Extraction

The trace level determination of five benzalkonium chloride (BAC) compounds in soil was investigated using ion-pairing liquid chromatography-tandem mass spectrometry. The instrumental intensities of the target compounds were compared with four ion-pairing reagents, and 30 mM perfluoroheptanoic acid (PFHA) was selected as the best reagent. An ultrasonically assisted extraction method was developed for soil. The optimum extraction conditions were as follows: extraction solvent, 30 mM PFHA in an acetone:acetonitrile (1:1, vol/vol) mixture; pH 7; volume, 20 mL; and extraction time, 30 min. Under the established conditions, the limits of quantification ranged from 0.3 to 3.6 g/kg, the accuracy ranged from 90.1 to 112%, and the intra- and interday relative standard deviations were <13% at concentrations of 10, 50, and 100 g/kg. The developed method was used to analyze target compounds in 50 soil samples collected from 40 survey sites and 10 background sites. The total BACs were within a concentration range of 0.001-28.5 mg/kg in soil. The developed method confirms the existence of BAC residues in real soil, providing an important tool to evaluate the behavior of disinfectants in soil and can be used to study residual amounts of BACs in soil.