Novel coupling reactions of phytochemicals with sulfa drugs and their applications in the determination of nitrite at trace level in environmental samples

Twelve spectrophotometric methods based on new reactions for the determination of trace amounts of nitrite in environmental samples were developed. Replacement of toxic reagents was explored to attain the standards of clean chemistry. These methods utilize two classes of compounds namely; phytochemicals and sulfonamides, in the presence of limited amounts of sodium hydroxide. The methods were based on the oxidation of sulfanilamide (SAA), sulfadoxine (SDX), sulfamethoxazole (SMX) or sulfadiazine (SDZ) by nitrite in sodium hydroxide medium and coupling with cardol, cardanol or anacardic acid which yielded yellow, orange and orange red color derivatives having an absorbance maximum in the range 430, 460 and 470 nm, respectively. The colors developed were stable for about 3 h. Beer’s law was obeyed for nitrite in the concentration range 0.08–0.90, 0.16–1.04, 0.08–0.80 and 0.08–0.80 μg ml−1 for cardol; 0.80–4.40, 1.60–5.72, 0.52–5.20 and 0.80–4.40 μg ml−1 for cardanol and 0.80–5.70, 1.04–6.20, 1.30–5.20 and 0.80–4.00 μg ml−1 for anacardic acid, respectively. The reaction conditions and other important analytical parameters were optimized to enhance the sensitivity of the methods. Interference if any, by non-target ions was also investigated. The methods were applied determining nitrite in environmental samples. The performances of these methods were evaluated in terms of Student’s t-test and variance ratio F-test to find out the significance of the proposed methods over the reference spectrophotometric method.