Simultaneous determination of nitrate and nitrite in vegetables by poly(vinylimidazole-co-ethylene dimethacrylate)...

Simultaneous determination of nitrate (NO₃^‾) and nitrite (NO₂^‾) in vegetables was performed on a poly(1-vinylimidazole-co-ethylene dimethacrylate) (VIM-EDMA) monolithic column by capillary liquid chromatography (LC) with UV detection. Good linearity (0.5-100 μg mL^-1 i.e. 12.5 -2500 μg g^-1 in vegetables) was obtained with coefficient of determination > 0.996. Limits of detection (signal-to-noise ratio: S/N= 3) were estimated at 0.06 and 0.05 μg mL^-1, which corresponded to 1.50 and 1.25 μg g^-1 for NO₂^‾ and NO₃^‾, respectively, in vegetables. The limits of quantification (S/N= 10) were estimated at 0.17 and 0.16 μg mL^-1 (4.25 and 4.00 μg g^-1 in vegetables) for NO₂^‾ and NO₃^‾, respectively. Although the detection limits were relatively higher than other LC-UV techniques, this proposed method offered satisfactory sensitivity for complying the Acceptable Daily Intake (ADI) levels set by EU to monitor the occurrence of NO₂^‾ and NO₃^‾in vegetables. The intra-day/inter-day precision (0.14-3.35%/0.06-6.93%) and accuracy (90.33-103.32%/96.00-101.26%) were also examined for method validation. No obvious carry-over and decline of separation efficiency were observed for more than 200 analyses of real samples. The occurrence of NO₂^‾ and NO₃^‾in various vegetable samples was investigated to demonstrate the potential of utilizing the developed polymeric monolith-based capillary LC-UV method for food safety application.