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.
Keywords: Nitrate; Nitrite; Poly(vinylimidazole-co-ethylene dimethacrylate) monolithic stationary phase; Vegetables.
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