Abstract: Eighty layers of 32-week-old laying hens weighing about 1.6 kg were chosen in this experiment. For test groups, the dose of sulfamonomethoxine was set at 159 mg·L^-1 (label recommended maximum dose) and 79.5 mg·L^-1 in drinking water, respectively. After continuous medication for 5 days, the addition of sulfamonomethoxine in drinking water was stopped and eggs were collected every day. Sulfamonomethoxine residues in egg samples were pretreated with QuEChERS method and quantified by ultra performance liquid chromatography-mass spectrometer/mass spectrometer (UPLC-MS/MS). The results showed that the residual amount of sulfamonomethoxine in 159 mg·L^-1 test group was 2 497.3, 220.1, 38.9, 6.0, 1.3, 0.5, 0.1 μg·kg^-1 on the 1^st, 3^rd, 5^th, 10^th, 16^th, 20^th, 24^th day, respectively. The residues of sulfamonomethoxine in 79.5 mg·L^-1 test group were 694.3, 45.2, 15.5, 1.5, 0.1 μg·kg^-1 on the 1^st, 3^rd, 5^th, 10^th, 16^th day, respectively. Sulfamonomethoxine depletion rate in eggs was 0.4-0.6 μg·kg^-1·d^-1. According to the maximum residue limit (MRL) of sulfamonomethoxine in animal tissue set by China, the residual amount in eggs was lower than MRL on 5^th and 3^rd day in 159 mg·L^-1 and 79.5 mg·L^-1 test group, respectively, without drug application. To guarantee food safety, the proposed withdrawal period should be set at more than 5 days if the label recommended maximum dose of sulfamonomethoxine was applied.

Key words: egg, ultra performance liquid chromatography-mass spectrometer/mass spectrometer, sulfamonomethoxine, elimination, withdrawal period