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 SiO 2 @Fe 3 O 4 (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 0.970V vs. Ag/AgCl. Nitrate was first reduced to nitrite and accumulated at the electrode surface by applying the accumulation potential of −0.300V and then oxidized at 0.970V vs. Ag/AgCl. The limit of detection was found to be 0.034mgL −1 (0.625μmolL −1 ) and 5.4mgL −1 (87μmolL −1 ) for NO 2 – and NO 3 – , respectively. The effects of different cations and anions on the determination of NO 2 – and NO 3 – , 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 NO 2 – and NO 3 – in several foodstuffs and water samples.