The capability to test for residues of veterinary drugs in animals is vital for the food industry. Food manufacturers are required to demonstrate the compliance of their products with stringent customer and legal specifications. The objective of this application is to improve the sample preparation of growth promoting beta-agonists from pig tissue. The preparation is based on solid phase extraction using Bond Elut Plexa PCX. The mixed mode Plexa PCX concentrates the basic beta-antagonists while eliminating the neutral and acidic interfering components of the matrix, providing improved sensitivity and analytical recovery.