Chemiluminescence determination of sulphadiazine in drugs by flow injection analysis using the peroxyoxalate reaction in micellar medium

Peroxyoxalate chemiluminescence (PO-CL) is an indirect type of CL which allows the detection of native fluorophores or compounds derivatized with fluorescent labels. We propose a flow injection analysis (FIA) configuration based on the use of a two-injection valve system for the introduction of both PO and derivatized analyte solutions in the flow system, avoiding the problems arising from the use of organic solvents, such as acetonitrile, as no special tubes nor special pumps are required. Furthermore, the use of micellar media (sodium dodecyl sulphate, SDS) as a carrier and the addition of tetrahydrofurane (THF) in the PO solutions increase both the solubility and stability of POs, avoiding their rapid degradation in water. The proposed CL-FIA system has been applied to the determination of sulphadiazine (a sulphonamide mainly used in the treatment of urinary tract infections for human and veterinary use) using bis[2,4,6-trichlorophenyl]oxalate (TCPO) as CL precursor, H2O2 as oxidant, imidazole as a catalyst and fluorescamine as the fluorescent derivatizing agent. The optimization of variables was carried out by means of experimental designs and the method showed a LOQ of 379 μg l−1 (calibration range 126–2000 μg l−1). It has been satisfactorily applied to the quantification of sulphadiazine in pills for human use and ampoules for veterinary use.