A fast liquid chromatography time-of-flight mass spectrometry (LC-TOFMS) method has been developed for simultaneous quantitative multiclass determination of residues of selected antibiotics and other veterinary drugs (benzalkonium chloride, ethoxyquin, leucomalachite green (LMG), malachite green (MG), mebendazole, sulfadiazine, sulfadimethoxine, sulfamethazine, sulfamethizole, sulfanilamide, sulfapyridine, sulfathiazole and trimethoprim) in shrimps. Different sample treatment methodologies were tested for the extraction of the targeted species based on either liquid partitioning with different solvents, solid-phase extraction or and matrix solid-phase dispersion. The final selected extraction method consisted of solid-liquid extraction protocol using acetonitrile as solvent followed by a clean-up step with primary secondary amine (QuEChERS). Recovery rates for the extraction of the selected multiclass chemicals were in the range 58-133%. Subsequent identification, confirmation and quantitation were carried out by LC-TOFMS analysis using a reverse-phase C(18) column with 1.8 μm particle size. The confirmation of the target species was based on accurate mass measurements of the protonated molecules ([M+H](+)) and their fragment ions, obtaining routine accuracy errors lower than 2 ppm in most cases. The optimized LC-TOFMS method displayed excellent sensitivity for the studied analytes, with limits of detection (LODs) in the range 0.06-7 μg kg(-1). Finally, the proposed method was successfully applied to the analysis of 12 shrimp samples collected from different supermarkets, showing the potential applicability of the method for ultratrace detection of these chemicals in such complex matrix.

A gas chromatographic method is presented for the simultaneous determination of the antiscald ethoxyquin and the fungicides imazalil and iprodione in peel and pulp of Blanquilla pears. Fruits were cold-stored in commercial chambers in normal atmosphere and in controlled atmosphere with low oxygen content (oxygen and carbon dioxide were held at 2.5% and 1.5%, respectively). The method uses gas-liquid chromatography (GLC) with an alkaline flame ionization detector (detector of N-P, NPD) and allows the detection of the mentioned compounds to minimum levels of 0.08-0.12 mg/kg in fresh fruit. With this system the evolution of residues in fruit was monitored throughout the period of cold storage. In the surveys carried out the residue levels of these compounds were found to be below the limits allowed by the legislation of European Union. For the three studied products residues in pulp are lower and disappear more quickly than in peel.

A method is described for the determination of ethoxyquin (1,2-dihydro-6-ethoxy-2,2,4-trimethylquinoline) in paprika and chili powder. Ethoxyquin is extracted from the spice with hexane and partitioned into 0.3N HCl. After adjusting the solution to pH 13-14, ethoxyquin is extracted into hexane, and the hexane layer is evaporated to dryness. An acetonitrile solution of the residue is then analyzed by reverse phase high pressure liquid chromatography with detection at 254 nm. The mobile phase is water-acetonitrile with ammonium acetate buffer. Recoveries from samples fortified at 50, 100, and 200 ppm averaged 92% with a coefficient of variation of 2.3%. The method was applied to a number of commercial samples of paprika and chili powder. Ethoxyquin was found in paprika samples at levels up to 63 ppm and in chili powder samples at levels up to 20 ppm.

A high pressure liquid chromatographic (HPLC) method has been developed for the determination of ethoxyquin (1,2-dihydro-6-ethoxy-2,2,4-trimethyl-quinoline) in milk. Milk solids are precipitated by adding acetonitrile, and the water-acetonitrile supernate is washed with hexane to remove fat. Addition of sodium chloride causes the water-acetonitrile solution to separate into an aqueous phase and an acetonitrile phase, thus separating ethoxyquin from most water-soluble impurities. A large volume of water is then added to the acetonitrile layer and ethoxyquin is partitioned into hexane, which is removed at reduced pressure. The residue is dissolved in the mobile phase and analyzed on a 4.6 mm id X 250 mm Ultrasphere ODS column using fluorescence detection (excitation 230 nm; 418 nm cutoff filter). Water-acetonitrile with a diethylamine-acetic acid buffer is the mobile phase. Recoveries from samples fortified at 1, 5, and 10 ppb averaged 78% with a coefficient of variation of 5.0%. Low levels (less than 1 ppb) of apparent ethoxyquin were found in commercial milk samples that were analyzed by using the method.

Salmons of two different sizes (group I; 22--30 g, group II; 600--1450 g) were tested for ethoxyquin (EMQ) residues after fed ad libitum a diet supplied with the therapeutic level of 900 ppm EMQ for 2 months. The sums of residues of EMQ and possible metabolites having similar fluorescence characteristics were determined by a fluorimetric method. The percentage of unmetabolized EMQ present was estimated using a gas chromatographic-mass spectrometric (GLC-MS) method measuring only unchanged EMQ. For both methods the detection limit was 0.1 ppm. EMQ residues were also fluorimetrically estimated in muscle tissue of small salmons fed a diet preserved with 150 ppm EMQ for 2 months. At termination of feeding the diet supplied with 900 ppm EMQ, residues measured fluorimetrically in muscle tissue of salmons in both groups were averaging 0.7 ppm. Approximately one third was unchanged EMQ. From salmons of group II blood, kidney and hepatic tissue were also analyzed at termination of feeding and residues averaging 0.3, 0.8 and 1.8 ppm respectively were estimated. The elimination of EMQ from muscle tissue is illustrated in Fig. 1. No residues could be detected 9 days following termination of feeding the therapeutic level of EMQ. In muscle tissue of salmons fed the diet preserved with 150 ppm EMQ, residues ranging from 0.1 to 0.3 ppm of EMQ and possible metabolites were found in 9 of 10 samples obtained from 20 salmons in group I. For an evaluation of EMQ used as a feed additive (150 ppm), further studies were recommended. The diets used in the experiment contained 88 and 830 ppm EMQ respectively measured fluorimetrically at the end of the experiment. Approximately 88% of the residues in the feed was unchanged EMQ. It is suggested that most information regarding the hygienic aspects of residues in muscle tissue is obtained by fluorimetry which is therefore recommended for determination of EMQ residues in tissues. The GLC-MS method, however, is recommended for estimation of EMQ levels in feed.

Ethoxyquin is a chemical antioxidant used in feeds, ingredients, fats, and oils. A liquid chromatographic (LC) method for determination of ethoxyquin was developed. The method involves acetonitrile extraction of the sample and isocratic C18 reversed-phase chromatography with ammonium acetate buffer-acetonitrile as mobile phase and fluorescence detection. A collaborative study of the determination of ethoxyquin in various meals and extruded pet foods was conducted by The Iams Company Research Laboratory. Eleven laboratories analyzed 16 samples (including 2 blind duplicates) consisting of 7 meat meals and 9 extruded pet foods. Sample means ranged from 0.25 to 289 ppm. Repeatability standard deviations ranged from 0.08 to 3.2 ppm, and repeatability relative standard deviations ranged from 4.5 to 32%. Reproducibility standard deviations ranged from 0.12 to 13 ppm, and reproducibility relative standard deviations ranged from 4.5 to 55%. The LC method for determination of ethoxyquin in feeds has been adopted first action by AOAC INTERNATIONAL.

A reverse-phase high-performance liquid chromatographic (HPLC) method was employed for analysis of nicarbazin [1:1 mixture of 4,4'-dinitrocarbanilide (DNC) and 2-hydroxy-4, 6-dimethyl-pyrimidine] in chicken eggs. Nicarbazin residues were analysed by determining the DNC of nicarbazin. HPLC of the DNC portion of nicarbazin was performed with a reverse-phase mu-Bondapak C18 column, using a mobile phase of acetonitrile-water (7:3, v/v). A variable-wavelength detector set at 340 nm, 0.02 AUFS, and a recorder set at 4 mm/min were used for the detection. The standard curve for nicarbazin was linear within the range 0.05-2.0 micrograms/ml. The recovery of nicarbazin added to eggs was 90.2%. The detection limit of nicarbazin in this analytical method was 0.005 micrograms/ml. Nicarbazin was detected in 10% of eggs obtained by feeding chickens with a diet contaminated with nicarbazin within the range 0.07 to 1.39 micrograms/g, but it was not detected in eggs obtained commercially.