Mary C. Carson

Oxytetracycline residues in a freshwater recirculating system

Abstract When oxytetracycline (OTC) medicated feed is fed to fish in a recirculating aquaculture system, antibiotic residues could accumulate in fish tissue, water, biofilter sand and sediment to a greater extent than in single pass or serial reuse aquaculture systems. In two trials, oxytetracycline-medicated feed (3 g active ingredient per pound of feed) was fed to adult rainbow trout at 1% b.w. per day for 10 days. OTC residues were assayed in fish muscle (with skin attached), water, sediment (e.g., fish feces, uneaten feed) and biofilter sand. For both trials, oxytetracycline was detected during the 10 days of treatment in all matrices assayed. In trout muscle, OTC concentrations increased to an average of 1.8 μg/g by day 10 of treatment and then declined to

Confirmation of multiple tetracycline residues in milk and oxytetracycline in shrimp by liquid chromatography-particle beam mass spectrometry.

A confirmation procedure is described for detection of residues of six tetracyclines in bovine milk, and oxytetracycline in shrimp. Residues are extracted from milk or shrimp tissue using metal chelate affinity chromatography. The extracts are desalted, further concentrated using polymeric solid-phase extraction, and chromatographed on a polymeric reversed-phase column. Analysis is by methane negative ion chemical ionization on a quadrupole mass spectrometer using a particle beam interface. Data are acquired in partial scan mode, monitoring from m/z 378 to m/z 480. The procedure was validated with control milk and shrimp, fortified milk (30 ng/ml) and shrimp (100 ng/g), and milk and tissue from animals treated with the drugs.

Simultaneous screening and confirmation of multiple classes of drug residues in fish by liquid chromatography-ion trap mass spectrometry

LC-ion trap mass spectrometry was used to screen and confirm 38 compounds from a variety of drug classes in four species of fish: trout, salmon, catfish, and tilapia. Samples were extracted with acetonitrile and hexane. The acetonitrile phase was evaporated, redissolved in water and acetonitrile, and analyzed by gradient chromatography on a phenyl column. MS(2) or MS(3) spectra were monitored for each compound. Qualitative method performance was evaluated by the analysis over several days of replicate samples of control fish, fish fortified with a drug mixture at 1 ppm, 0.1 ppm and 0.01 ppm, and fish dosed with a representative from each drug class. Half of the 38 drugs were confirmed at 0.01 ppm, the lowest fortification level. This included all of the quinolones and fluoroquinolones, the macrolides, malachite green, and most of the imidazoles. Florfenicol amine, metronidazole, sulfonamides, tetracyclines, and most of the betalactams were confirmed at 0.1 ppm. Ivermectin and penicillin G were only detectable in the 1 ppm fortified samples. With the exception of amoxicillin, emamectin, metronidazole, and tylosin, residue presence was confirmed in all the dosed fish.

Ion-pair solid-phase extraction

Solid-phase extraction (SPE) is a technique widely employed by analytical chemists. SPE cartridges are available in a wide variety of formats containing media with diverse chemistries. This paper will review ion-pair SPE, one of the less frequently applied, and presumably less well-known techniques. Advantages of this technique over more conventional reversed-phase or ion-exchange SPE include selectivity, compatibility with rapid evaporative concentration, and potential application to multiclass multiresidue analysis.

Confirmation of spectinomycin in milk using ion-pair solid-phase extraction and liquid chromatography-electrospray ion trap mass spectrometry

A confirmation procedure is described for residues of spectinomycin in bovine milk. Spectinomycin is extracted from raw milk using ion-pair reversed-phase solid-phase extraction. The extracts are ion-pair chromatographed on a polymeric reversed-phase column and analyzed on a quadrupole ion trap mass spectrometer equipped with an electrospray interface. MS-MS data are acquired in the scan mode of product ions deriving from m/z 333, the protonated molecular ion. The estimated limit of confirmation is between 0.05 and 0.1 microg/ml. The procedure was validated with control milk, fortified milk (0.1-5.0 microg/ml), and milk from cows dosed with spectinomycin.

Approaches to the Detection and Confirmation of Drug Residues in Milk

The possible presence of trace residues of veterinary drugs in milk is a subject of major concern for regulatory agencies, the dairy industry, and consumers. All New Animal Drug Applications (NADAs), in addition to showing efficacy and safety of the drug to the animal, must also show that treatment of the animal will result in no hazardous residues entering the human food chain. NADAs therefore include methodology to detect tissue residues. Part of the review process at FDA’s Center for Veterinary Medicine (CVM) is to evaluate the drug sponsor’s residue method.