A novel application of matrix solid-phase dispersion for determination of doxycycline and flumequine residues in milk

A novel version of matrix solid-phase dispersion (MSPD) for isolation of doxycycline (DC) and flumequine (FL) in milk was established. The MSPD procedure involves blending of sample with solid support material, usually silica with bonded C18 chains. In the work presented, bare siliceous sorbents were applied i.e., kieselguhr, wide-pore silica gel and Chromosorb WAW. The sorbents were blended with the spiked milk using sorbent to milk ratio 4:1 w/w. The "pastes," formed in that way, were put into the syringe and defatted with hexane. Then, dichloromethane was used to elute FL. The mixture of 0.5 M citric acid/methanol/2-propanol (1:3:1) or 0.5 M citric acid/methanol (1:9) were used to elute DC. RP-HPLC and NP-HPLC were used for simultaneous determination of the antibiotics. It was possible to detect the antibiotics in milk at 100 ppb level. Chromosorb proved to be the optimal MSPD sorbent.