Abstract
A simple, low-cost, sensitive and selective method for the determination of trace quantities of nitrite in foods such as cheese and cured meat using diffuse ultraviolet-visible reflectance was developed. It is based on the reaction of nitrite with sulphadiazine and α-naphthol, which produces a coloured product in basic medium. The reaction is carried out directly in the measuring cell. For cheese the limit of detection (LOD), expressed as NaNO2, was estimated to be about 2.0 × 10−2 mg l−1 (2.9 × 10−7 mol l−1) in the final measuring solution and 0.17 mg kg−1 in cheese (2.5 × 10−6 mol kg−1). The relative standard deviation (RSD) varied from 5% to 8% depending on the sample. For meat the LOD was estimated to be about 2.0 × 10−2 mg l−1 (2.9 × 10−7 mol l−1) in the final measuring solution and 0.13 mg kg−1 in meat (1.9 × 10−6 mol kg−1). The RSD varied from 3% to 6% depending on the sample. The results of the proposed method were also compared with those obtained with the official method using the statistical Student's t-test and F-test procedures.
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Acknowledgements
The authors are grateful to TWAS & CNPq for financial support and fellowships. They also thank FAPESP for financial aid and Professor Carol H. Collins for the English revision of the manuscript.