A new chemically modified electrode was constructed for rapid, simple, accurate, selective and highly sensitive determination of nitrite and nitrate in mixture using square wave stripping voltammetry (SWASV). The electrode was prepared by incorporation of synthesized nanocomposite 3,6-bis(2-[2-sulfanyl-ethylimino-methyl]-4-(4-nitro-phenylazo)-phenol)pyridazine coated SiO2@Fe3O4 (L-SCMNPs) in carbon paste electrode. The prepared nanocomposite was characterized by SEM, XRD and FTIR measurements. Nitrite ion was oxidized at the surface of the modified electrode at 0.970 V vs. Ag/AgCl. Nitrate was first reduced to nitrite and accumulated at the electrode surface by applying the accumulation potential of -0.300 V and then oxidized at 0.970 V vs. Ag/AgCl. The limit of detection was found to be 0.034 mg L-1 (0.625 mu mol L-1) and 5.4 mg L-1 (87 mu mol L-1) for NO2- and NO3-, respectively. The effects of different cations and anions on the determination of NO2- and NO3-, in the presence of each other. were investigated and found that the electrode is highly selective. The proposed chemically modified electrode was used to the determination of NO2- and NO3- in several foodstuffs and water samples. (C) 2012 Elsevier Ltd. All rights reserved.