Determination of 2,4-dichlorophenoxyacetic acid and its metabolite in soils by gas chromatography-mass spectrometry after pre-concentration using magnetic charcoal based on rice husk

Abstract

A method for determining 2,4-dichlorophenoxyacetic acid (2,4-D) and its metabolite 2,4-dichlorophenol (2,4-DСР) in soils is proposed. 2,4-D and 2,4-DСР were extracted from the soil by an alkali solution. The analytes were recovered from the extract using a sorbent based on magnetite nanoparticles and coal obtained by burning rice husk, and desorbed by methanol. 2,4-D and 2,4-DСР in the concentrate thus obtained were converted to methyl esters and determined using the GC-MS method. The quantification limit (LOQ) of 2,4-D and 2,4-DCP were 3.0 μg/kg and 0.08 μg/kg, respectively. Leached black soil (from the border of Stavropol and Krasnodar Territories) was selected as a real object for analyzing the distribution of the herbicide “Ballerina” (ethylhexyl ester of 2,4-D) and its degradation product. A day after applying the herbicide, the concentration of 2,4-D in the surface layer of the soil was 119 μg/kg. Atmospheric precipitation has a significant effect on motion of 2,4-D along the soil profile. The most significant decrease in the concentration of 2,4-D was observed between 3 and 10 days after application of the herbicide. A month after application of the herbicide, the concentration of 2,4-D was 31, 18 and 11 μg/kg at the depths of 10, 30 and 50 cm, respectively; no 2,4-D was detected in the surface soil layer. Detectable amounts of 2,4-DСР appeared on 16-th day after application of the herbicide; 2,4-DСР degrades much slower than 2,4-D. After 1.5 months, the concentration of 2,4-DСР was 0.53, 0.45 and 0.22 μg/kg at the depths of 10, 30 and 50 cm, respectively. At the same time, 2,4-D was not detected throughout the soil profile.