Multiresidue analysis of banned substances in livestock drinking water by high-performance liquid chromatography-mass spectrometry

Abstract

Residues from many classes of antimicrobial drugs have become food safety issue of public concern due to their potential to pose risks to consumers. Antimicrobial drugs such as nitrofurans (nitrofurazone (NFZ), nitrofurantoin (NFT), furazolidone (FZD) and furaltadone (FTD)); nitroimidazoles (metronidazole (MNZ), ronidazole (RNZ) and dimetridazole (DMZ)); and chloramphenicol (CAP) are strictly prohibited in the livestock industry. Nevertheless, misuses of these substances are still present in animal feed and drinking water. This work focused on development of liquid chromatography coupled to an ion trap mass spectrometer (LC-MS ion trap) for the simultaneous separation of these drugs in animal drinking water. The HPLC analysis was performed on a Prodigy ODS-3 column, 2.0x150 mm, 5 μm with a guard cartridge at a flow rate of 0.2 mL/min, column oven temperature 40°C, and injection volume 10 μL. Factors affecting HPLC separation (i.e. buffer pH and concentrations), solid phase extraction (SPE), and ion trap MS using electrospray ionization (ESI) in tandem mass spectrometry mode (MS/MS) were optimized. The eight antimicrobial agents were separated in 22 min using gradient elution of acidified water (pH 5.0) and acetonitrile, nebulizer gas at 35 psi, drying gas and dry temperature at 9 L/min and 325 °C, respectively. The linearity was acceptable (r2 = 0.979 - 0.999) with the precision and accuracy range from 3.4 - 26.6% and 88.4 - 110.1%, respectively. Limit of detection (LOD) and limit of quantitation (LOQ) for each compound was in a range of 0.002 - 0.06 μg/L and 0.005 - 0.25 μg/L, respectively. The validated method was applied to simultaneous determination of eight antimicrobial drugs in 40 animal drinking water samples collected from standard farms in Thailand. The prohibited drugs were not detected in any samples. This finding may reflected the efficiency of residue control measures in livestock production that have been strictly applied since 2002.