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

•We used a novel ionic liquid [BMIM]MR for nitrite sensing for the first time.•60-fold improvement of sensitivity was obtained of nitrite detection.•Activation energy and the apparent rate constant were also investigated.•Trace amounts of nitrite in some significant real samples were determined.•The method could be deployed in environmental and food monitoring.

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%.