Multi-Residue Analysis of Herbicides in Soil with an UPLC-ESI-MS Method

A rapid and sensitive method was developed for the determination of 51 herbicides in soil by ultra-performance liquid chromatography-electrospray ionization-mass spectrometry (UPLC–ESI–MS). Using acetonitrile effectively extracted 22 kinds of triazine and other basic herbicides, and using 90:10 v/v acetonitrile-phosphate buffer (pH = 7.5) effectively extracted another 29 herbicides. The extract has not cleaned up further. Chromatographic separation was achieved within 10 min using gradient elution with acetonitrile–water as a mobile phase for 22 triazine and phenylurea herbicides, and with 5 mM ammonium acetate containing 0.1% formic acid aqueous solution–acetonitrile as a mobile phase for another 29 herbicides. The response was linear over two orders of magnitude with correlation coefficients (r²) higher than 0.99. The limits of quantification for the herbicides varied from 0.2 to 20 µg kg^?1. The intra- and inter-day precisions (relative standard deviation, RSD) were 2.2–9.3% and 5.7–17.1%, respectively. The average recovery varied from 61.6 to 112% with the RSD of 1.6–11.3%. Analyzing 51 soil samples from 17 counties formed the basis of this method. Three herbicide residues were found in four counties. Atrazine residue in soil for 17 counties was found; its content was 0.4–9.8 μg kg^?1. Nicosulfuron residue in soil for two counties was found, with a high up to 133 or 1317 μg kg^?1. Propazine (0.3 and 1.34 μg kg^?1), atratone (2.14 and 3.93 μg kg^?1), and cynanazine (0.34 μg kg^?1) in soils for some counties were also found. The validated method can ensure the rapid multi-class, multi-residue analysis at low μg kg^?1 level for 47 herbicides in soil. The developed method provides an effective analytical basis for controlling herbicide dosage, investigating their distribution and degradation, and evaluating their hazards on the environment and human health.