Ion chromatography for determination of nitrite and nitrate in seawater using monolithic ODS columns

A fast and highly sensitive ion chromatographic method using monolithic ODS columns was developed for the determination of nitrite (NO2−) and nitrate (NO3−) in seawater. Two monolithic ODS columns (50 mm × 4.6 mm i.d. + 100 mm × 4.6 mm i.d.) connected in series were coated and equilibrated with 5 mM cetyltrimethylammonium chloride (CTAC) aqueous solution. The column efficiency with 0.5 M NaCl as the mobile phase did not decrease in spite of the increase in flow rate of the mobile phase. Thus, good chromatograms were obtained within 3 minutes for NO2− and NO3− in artificial seawater without interferences by coexisting ions. The detection limit (S/N = 3) with UV detection at 225 nm was 0.8 and 1.6 μg/L for NO2− and NO3−, respectively. The characteristics of the monolithic CTA+-coated ODS columns were discussed. The present method was successfully applied to the fast and sensitive determination of NO2− and NO3− in real seawater samples.