UPLC–MS/MS determination of ractopamine residues in retinal tissue of treated food-producing pigs

Ractopamine is a β2-adrenergic agonist, which reduces fat deposition and promotes muscle growth in animals for meat production. In the European Union countries, systematic monitoring and control of this contaminant residue is regularly performed by use of validated analytical methods of detection in different biological materials. The aim of the present study was to assess persistence of ractopamine in retina as a pigmented tissue by determination of its residues using UPLC–MS/MS as a quantitative confirmatory method after pig exposure to a ractopamine dose of 0.51 mg/kg b.w. Experimental group (n = 9) of pigs were orally administered ractopamine for 28 days and then randomly sacrificed (n = 3) on days 1, 3 and 8 of treatment discontinuation, whereas control animals (n = 3) were left untreated. Study results showed mean ractopamine residue concentrations of 110.36 μg/kg, 67.11 μg/kg and 89.93 μg/kg on days 1, 3 and 8 after withdrawal, respectively, indicating high accumulation of ractopamine in retina despite a low dose applied. These data pointed to high affinity of ractopamine for binding to the pigmented segment of the eye, thus supporting the use of pigmented tissues as matrices in the regulatory monitoring of this β2-adrenergic agonist.