Multitarget and suspect screening of antimicrobials in soil and manure by means of QuEChERS — liquid chromatography tandem mass spectrometry

Abstract

The present work aimed to develop an accurate analytical method for the simultaneous analysis of twenty-four antimicrobials in soil:compost and animal manure samples by means of ultra-high performance liquid chromatography coupled to a triple-quadrupole mass spectrometer (UHPLC-QqQ). For this purpose, the effectiveness of two extraction techniques (i.e. focused ultrasound solid–liquid extraction (FUSLE) and QuEChERS (quick, easy, cheap, effective, rugged and safe)) was evaluated, and the clean-up step using solid-phase extraction (SPE) was also thoroughly studied. The method was successfully validated at 10 μg·kg−1, 25 μg·kg−1, and 50 μg·kg−1 showing adequate trueness (70–130%) and repeatability (RSD < 30%), with few exceptions. Procedural limits of quantification (LOQPRO) were determined for soil:compost (0.45 to 7.50 μg·kg−1) and manure (0.31 to 5.53 μg·kg−1) samples. Pefloxacin could not be validated at the lowest level since LOQPRO ≥ 10 μg·kg−1. Sulfamethazine (7.9 ± 0.8 µg·kg−1), danofloxacin (27.1 ± 1.4 µg·kg−1) and trimethoprim (4.9 ± 0.5 µg·kg−1) were detected in soil samples; and tetracycline (56.8 ± 2.8 µg·kg−1), among other antimicrobials, in the plants grown on the surface of the studied soil samples. Similarly, sulfonamides (SAs), tetracyclines (TCs) and fluoroquinolones (FQs) were detected in sheep manure in a range of 1.7 ± 0.3 to 93.3 ± 6.8 µg·kg−1. Soil and manure samples were also analysed through UHPLC coupled to a high-resolution mass-spectrometer (UHPLC-qOrbitrap) in order to extend the multitarget method to suspect screening of more than 22,281 suspects. A specific transformation product (TP) of sulfamethazine (formyl-sulfamethazine) was annotated at 2a level in manure samples, among others. This work contributes to the efforts that have been made in the last decade to develop analytical methods that allow multitarget analysis of a wide variety of antimicrobials, including TPs, which is a complex task due to the diverse physicochemical properties of the antimicrobials.