A rapid, simple and reliable LC-MS/MS method, which can be used on a routine basis, was developed for the simultaneous detection of 8 penicillin antibiotics (amoxicillin, ampicillin, penicillin-G, penicillin-V, oxacillin, cloxacillin, nafcillin and dicloxacillin) in swine muscle and kidney. The antibiotics were extracted from samples with water and methanol. The extract was centrifuged, filtered and analyzed by liquid chromatography coupled with a tandem mass spectrometer (LC-MS/MS), using a C18 reversed phase column with water/acetonitrile gradient containing 0.05 % formic acid. Mass spectral acquisition was achieved in an electrospray positive ion mode by applying multiple reaction monitoring (MRM) of 2 fragment ion transitions to provide a high degree of sensitivity and specificity. The ion rations were consistent and could be used for confirmation of identity of the penicillin antibiotics. Recoveries of eight penicillins at three fortification levels (10, 20 and 40㎍/㎏) ranged from 79.8 to 102.4% and 72.8 to 103.4% in swine muscle and kidney, respectively. The coefficient of variation was than 9% in all samples. The estimated limits of quantification (LOQs) ranged from 1.0 to 3.2㎍/㎏ in swine muscle and kidney, respectively. The LOQs of this method are below the MRLs of penicillin antibiotics in animal tissues established in Korea and other countries.

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.

A reversed-phase high-performance liquid chromatography with tandem mass-spectrometric detection was developed and validated for the simultaneous analysis of 13 quinolones (orbifloxacin, sarafloxacin, marbofloxacin, ofloxacin, enrofloxacin, danofloxacin, pefloxacin, ciprofloxacin, norfloxacin, difloxacin, oxolinic acid, flumequine, nalidixic acid) in pork. The drugs were extracted from homogenized sample using acidic buffer (2% trichloracetic acid) and acetonitrile with ethyl acetate. Analysis was performed by liquid chromatograph with tandem mass spectrometry (LC-MS/MS) in positive mode for all quinolones. Mass spectral acquisition was performed in the multi reaction monitoring mode (MRM), selecting two structurally significant transitions per compound. Good linear relationship (R2=0.999) was observed at 6 concentrations of 2.5～100 ng/g. Satisfied recoveries (73.3～105.4%) of all quinolones were demonstrated in spiked pork at three levels from 5 to 20 ng/g. The limits of quantitation (LOQs) for quinolones ranged from 0.25 to 5.0 ng/g.

A simple, selective and sensitive procedure for the confirmation of 14 sulfonamide antibacterials in milk was developed. The milk samples were homogenized, extracted and deproteinized by acetonitrile and defatted by n-hexane. Analysis was performed by liquid chromatography with tandem mass spectrometry (LC-MS/MS) in positive mode for all 14 analytes. Mass spectral acquisition was performed in the multi reaction monitoring mode (MRM), selecting two structurally significant transitions per compound. The calibrations were performed in sample matrixes and the interference effect of sample matrixes on the ionization was effectively eliminated. Good linear relationship (R2=0.992～ 0.999) were observed at 6 concentrations of 2.5～100 ng/g. Satisfied recoveries (86.3～110.2%) of all sulfonamides were demonstrated in spiked milk at three levels from 5 to 20 ng/g. The limits of quantitation (LOQs) for sulfonamides ranged from 0.25～2.1 ng/g.