A new eco-friendly, rapid, and sensitive spectrophotometric method was developed to determine small quantities of nitrite, based on a diazotization mechanism. In an acidic solution, sulfathiazole was first diazotized with sodium nitrite, followed by adding phosphate buffer to form a yellow-colored compound, which showed maximum absorption at 450 nm, without the need for the addition of coupling agents such as N-(1-naphthyl) ethylenediamine. The effects of reagents amount and the optimal experimental conditions were examined by Central composite design. The simplified method presented a wide linear range of nitrite between 0.091 μg mL-1 and 1.47 μg mL-1, a sensitivity of 0.447 Abs mL µg-1, a determination coefficient of 0.998, and a low limit of detection of 0.053 μg mL-1. The simplified method was found to be comparable to the Griess method. It was evaluated for the measurements of nitrite using the accuracy profile approach. The validation procedure results established that 80% of the future results would be within the acceptability limit of 10% over the validation domain ranging from 0.174 μg mL-1 to 1.37 μg mL-1. The developed method was furtherly applied in the determination of nitrite using a developed paper-based analytical device that detected a nitrite concentration of 3 μg mL-1 which is considered by the World Health Organization to be the maximal permissible limit of nitrite in drinking water.
Keywords: Accuracy profile; Central composite design; Griess method; Nitrite; Paper-based analytical device; Spectrophotometric method.
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