High performance liquid chromatographic determination of trimethoprim residues in egg yolk and albumen in a feeding experiment

In a feeding experiment, the residues of trimethoprim (TMP) in egg yolk and albumen were determined by high performance liquid chromatography (HPLC). Laying hens were divided into four groups. The first group was designated as control and fed with TMP free diet during the experimental period. The second, third and fourth groups were administered with the feeds containing 4 p.p.m., 16 p.p.m. and 56 p.p.m. TMP, respectively, for 19 days and, thereafter, fed with TMP free diet. TMP was mainly found in yolk in all the three administered levels. In the medication period, the average concentration of TMP in the yolk of the second, third and fourth groups was 0.05, 0.25, and 0.90 p.p.m., respectively. After withdrawal of medication, the residues of TMP in yolk in the second, third and fourth groups decreased below the detection limit at 0.02 p.p.m. on days 4, 9, and 11, respectively.