A liquid chromatographic-tandem mass spectrometric (LC-MS/MS) multi-residue method for simultaneous quantification and identification of 37 anthelmintic veterinary drug residues (including benzimidazoles, macrocyclic lactones, and flukicides, levamisole, pyrantel and niclosamide) in milk has been developed and validated. For sample preparation, we used a simple modification of the QuEChERS (quick, easy, cheap, effective, rugged and safe) method, which was initially developed for analysis of pesticide residues. Anthelmintic residues were extracted into acetonitrile:methanol (9:1, v/v) using sodium chloride to induce liquid-liquid partitioning followed by dispersive solid phase extraction for cleanup. The extract was concentrated into dimethyl sulphoxide, which was used as a keeper to ensure that analytes remain in solution. Using rapid polarity switching in electrospray ionization, a single injection was capable of detecting both positively and negatively charged ions within a 15 min run time. The Limit of detection (LOD) and the Limit of quantification (LOQ) method ranged from 0.1 ng/g to 4.4 ng/g and from 0.3 ng/g to 14.6 ng/g, respectively. Validation of the developed method was based on international guidelines. Average recoveries ranged from 70% to 120%, except for 54.7% at 0.5× MRL (rafoxanide) and 69.0% at 0.5× MRL (closantel). The coefficient of variation for the described method was less than 15% over the range of concentrations studied. The result of the method was verified successfully by participation in a proficiency study for analysis of anthelmintic drugs.

A confirmatory method based on liquid chromatography with tandem mass spectrometry was developed for determination of 12 aminoglycosides in milk. Extraction of aminoglycosides from milk was performed using by liquid extraction using a 10 mM phosphate buffer containing 2% (w/v) trichloroacetic acid, followed by performance of a solid-phase clean-up procedure on a hydrophilic-lipophilic balance solid-phase extraction (HLB SPE). Ion-pair chromatography, using a mixture of 20 mM heptafluorobutyric acid (HFBA) in water and acetonitrile as the mobile phase, was used for retention of aminoglycosides on a reversed-phase C18 column. Mass spectral acquisition was performed in the multiple reaction monitoring mode, selecting two precursor ion>product ion transitions for each target compound. Satisfied recoveries (70.1～109.6%) of all aminoglycosides were demonstrated in spiked milk at three levels from 50 ng/g to 200 ng/g. The coefficients of variation ranged from 3.2% to 14.0%. The limits of quantitation (LOQs) for aminoglycosides ranged from 2.5 ng/g to 40.3 ng/g.

The Korean National Residue Program consists of three sampling plans for domestic and imported foods of animal origin : monitoring, surveillance/enforcement and exploratory testing. Monitoring and surveillance/enforcement testing programs are routinely implemented by 17 Provincial Veterinary Services for domestic products and two regional offices of Animal, Plant and Fisheries Quarantine and Inspection Agency (QIA) for imported products, respectively. The exploratory testing is designed to test substances which are not included in the list of monitoring and enforcement testing programs controlled by headquarter of QIA. In 2010, the exploratory testing was carried out in domestic and imported foods of animal origin for 24 veterinary drugs including florfenicol, clavulanic acid, four quinolones (nalidixic acid, difloxacin, marbofloxacin, orbifloxacin), two anthelmintics (closantel, levamisole), two sedatives (azaperone, carazolol), six glucocorticoids (dexamethasone, betamethasone, flumethasone, prednisone, prednisolone, methylprednisolone), eight non-steroidal anti-inflammatory drugs (phenylbutazone, paracetamol, carprofen, flunixin, ketoprofen, meloxicam, tolfenamic acid, acetylsalicylic acid). In the total of 1,153 domestic samples, only florfenicol was detected from 17 pig muscles at levels of 0.2～614 ng/g. Of 17 positive pig muscles, 16 samples were non-violative and one sample was violative. In the total of 1,065 imported samples, florfenicol was detected at 0.4 ng/g in one pork. Also, flunixin was detected at 22 ng/g in one beef.

Various antimicrobial drug screen tests have been used in order to ensure food safety. However, the conventional screen teats, the Swab Test on Premises(STOP, USA), the Calf Antibiotic and Sulfa Teat(CAST, USA) and the European Economic Community 4-plate Test(FPT, EU) are not sufficiently rapid or sensitive enough to detect low levels of sulfa drugs in meat. We developed a new screen test kit for the determination of the antimicrobial residues in meat called the Bacillus megaterium Disk AssayBmDA). A comparison of BmDA with the older screen tests showed BmDA was as good as the older ones with several advantages. The new test kit is faster-it can be read in 4-6 hours instead of 16-18 hours. Moreover, BmDA can discriminate sulfa drugs from other antimicrobial drugs because p-aminobenzoic acid countacts the inhibiting action of sulfa drugs. Minimum detectable levels of sulfa drugs were significantly improved at the level of 0.025-0.1 ppm compared with the level of 1.0 ppm in FPT. A comparison of BmDA with the older screen tests in HPLC confirmed meat samples exeeded the Korean tolerance value of 0.1 ppm showed BmDA was the most sensitive in the microbiological screen tests. As the microbiological screen tests have already known, a person familiar with simple laboratory techniques should have no difficulty in using it to detect antimicrobial residues in meat. This would be a simple, economic method of antimicrobial residues detection which might be succesfully used by many laboratories.