A sensitive colorimetric method for the determination of nitrite in water supplies, meat and dairy products using ionic liquid-modified methyl red as a colour reagent

This paper describes a colorimetric approach to determine trace amounts of nitrite in water supplies, meat and dairy products using 1-butyl-3-methylimidazolium-modified methyl red ([BMIM]MR) as a colour reagent. The technique capitalises on the catalytic effect of nitrite on the oxidative degradation of [BMIM]MR by potassium bromate in acidic media. The absorbances were proportional to nitrite concentrations in the range of 8.70 × 10−2 to 4.17 μM with a detection limit of 1.64 × 10−2 μM. Compared with the method using methyl red as a colour reagent, 60 times improvement of sensitivity was obtained. Activation energy and the apparent rate constant for the catalytic reaction are 61.11 kJ mol−1 and 1.18 × 104 s−1, respectively. The proposed method was successfully applied for the analysis of nitrite in Yellow River water, chicken, and milk with recoveries ranging from 96% to 105%.