Use of Zinc Sulfanilic Spectrophotometry in a High School Chemistry Lab for Nitrate Analysis of Community Water Quality

This study examined four separate water quality analysis methods for high school chemistry students to detect nitrate levels in drinking water. The study selected one of the methods for students to use for analysis of nitrate levels in their school district. The sulfanilic acid, napththylethylenediamine (NED) spectrophotometry method was selected due to the reagent’s low toxicity, and also its accuracy. The zinc sulfanillic NED method was adapted to better fit into a 47-minute lab period. Students proceeded through stations in order to facilitate a complex procedure, and also increase testing accuracy. The four methods studied included the cadmium reduction method using a color wheel, cadmium reduction method spectrophotometry, direct U.V. absorption spectrophotometry, and zinc, sulfanilic acid, NED spectrophotometry. Two of the methods were found to have low accuracy: color wheel cadmium reduction, and direct U.V. absorption spectrophotometry. The accuracy tests found that: 36% of the chemistry students using the color wheel cadmium reduction method were within 2 mg/l of the nitrate standard, 77% of the students using the cadmium reduction spectrophotometry were within 2 mg/l of the standard. 73% of the students using sulfanilic acid, NED spectrophotometry were within 2 mg/l. The student testing found that seventy percent of the Buffalo City, Wisconsin residential well samples the students analyzed, using sulfanilic acid, NED spectrophotometry, exceeded safe level of 10 mg/l nitrate; with detected levels as high as 62.2 mg/l.