Chemiluminescence microflow injection analysis system on a chip for the determination of nitrite in food

A new microflow injection analysis (μFIA) system on a chip for the determination of nitrite is described. The chip is produced by using two transparent poly(methylmethacrylate) (PMMA) slices measured 50 × 40 × 5 mm, and the microchannels etched by CO₂ laser are 200 μm wide and 100 μm deep with the volume of reaction area about 1.8 μL. Nitrite is sensed by the chemiluminescence (CL) reaction of luminol with ferricyanide that is the product of the reaction of ferrocyanide with nitrite in acidic medium. The syringe pump with an accurate timer controls all reagents, including the sample. The linear range of the nitrite concentration is 8–100 μg L⁻¹ and the detection limit is 4 μg L⁻¹ (S/N = 3). The proposed method has good reproducibility with the relative standard deviation 4.1% for 50 μg L⁻¹ of nitrite (n = 9) and is very sensitive and simple. It has been successfully applied to the determination of nitrite in food.