Distribution and elimination of levamisole in eggs and tissues after oral administration to laying hens, determined by LC-MS/MS

Levamisole was administered to laying hens, and concentrations in eggs and tissues (thigh muscle, breast muscle, liver and kidney) were determined by a newly developed liquid chromatography tandem mass spectrometry method, which allowed trace level quantification of levamisole. The adopted analytical method showed good sensitivity, repeatability and percentage of recovery from spiked matrices. Maximum concentrations of levamisole were found on the first day after the administration (531.1 μg/kg in liver, 164.3 μg/kg in egg yolk, 130.7 μg/kg in kidney, 78.0 μg/kg in breast muscle, 70.7 μg/kg in thigh muscle and 64.0 μg/kg in egg white), after which there is a decline. The compound was rapidly eliminated from eggs, with a half-life of 1.3 days. Elimination appeared to be slower in thigh muscle (3.5 days), breast muscle (3.4 days) and liver (3.3 days). According to this experiment, the levamisole withdrawal periods calculated for eggs, liver, kidney, breast muscle and thigh muscle in laying hens were 14.1, 6.1, >4.0, 14.5 and 13.0 days, respectively. The longest time for levamisole residues to be completely released from tissues was seen in liver samples (37.4 days), followed by thigh muscle, breast muscle and kidney. Elimination from eggs was fastest (16.4 days for levamisole residues to drop below the method quantification limit).

Validation of an enzyme-linked immunosorbent assay for qualitative screening of neomycin in muscle, liver, kidney, eggs and milk

A rapid and sensitive enzyme-linked immunosorbent assay (ELISA) was used for the qualitative screening analysis of neomycin in food of animal origin (muscle, liver, kidney, eggs and milk) at levels corresponding to the European Union maximum residue limit (MRL) set for this substance. The method validation was performed according to the criteria of Commission Decision 2002/657/EC established for qualitative screening methods. In this regard, the following parameters were determined: detection capability (CCβ), specificity, detection limit (LOD), quantification limit (LOQ), recovery, precision, linearity and ruggedness. LODs ranged from 5.7 microg kg(-1) in kidney to 29.3 microg kg(-1) in milk; LOQs ranged from 11.4 microg kg(-1) in kidney to 59.7 microkg(-1) in eggs. The recoveries from spiked samples at the MRL, half the MRL and double the MRL levels ranged from 65.8% to 122.8%, with a coefficient of variation (CV) between 5.9% and 28.6%. The CCβ value was less than the MRL for all examined matrices. Moderate variations of some critical factors in the sample pretreatment for muscle, milk and eggs were deliberately introduced for ruggedness evaluation and had a slight but not statistically significant effect on method performance. The proposed method is suitable for qualitative screening analysis of neomycin in the above-mentioned food in conformity with current European Union performance requirements.