Veterinary diagnostic laboratories provide a variety of services to livestock producers and companion animal owners. One of these services is a general untargeted screening of animal tissues for veterinary drug residues. Results from this assay are used to determine animal cause of death or emergency treatment options in the case of toxic exposure. The established analytical methods used for this type of screening require a QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) extraction and cleanup along with a liquid or gas chromatography mass spectrometry (LC/MS or GC/MS) analysis. Although these current methods are sensitive they require several hours of sample preparation and instrument analysis time. This time-consuming and resource-intensive process can result in delayed results which puts more animals at risk when toxic exposure has occurred to a herd of livestock.

An alternative approach to this problem is to use ambient ionization technologies coupled with high resolution mass spectrometry. Ambient ionization technologies require minimal sample preparation and allow samples to be analyzed under atmospheric conditions. High resolution mass spectrometry uses exact mass to identify unknown analytes in complex matrices. Liquid microjunction surface sampling probe (LMJSSP) is an ambient ionization technology that extracts analytes directly from the sample surface. Presented here is an untargeted screening method using LMJSSP and high resolution mass spectrometry to quickly identify veterinary drug residues in animal tissues.

The LMJSSP-MS method uses a data-dependent scan function of a quadrupole orbitrap mass spectrometer to acquire product ion spectra from a tissue sample. The product ion spectra are processed using a customized untargeted identification workflow in Compound Discoverer software and searched against the mzCloud™ online mass spectral database. The LMJSSP-MS method identified a variety of veterinary drug residues including flunixin, tilmicosin, pentobarbital, phenytoin, ketamine, and xylazine. Multiple tissue types were analyzed including liver, kidney, muscle and spleen. Tissue samples came from several different species including bovine, porcine, equine, canine, and caprine. This method was applied to thin tissue sections as well as needle aspirate smears of tissue samples. The limit of identification (LOI) of this method for xylazine and ketamine is approximately 1 µg/g. The details of the method optimization will be discussed. Veterinary drug residues can be identified in tissue samples in less than an hour using this method. This novel LMJSSP-MS method is applicable to future veterinary diagnostic laboratory toxicology needs.