Determination of Chloride in the Rouge River with Ion-Selective Electrode

An analytical chemistry laboratory experiment for the determination of chloride in natural water and unknown aqueous samples with chloride ion-selective electrode (Cl-ISE) is presented. Water samples were collected from three sites along the Rouge River, Michigan, USA, over a period of several months and analyzed for chloride by students enrolled in a multi-section analytical chemistry course. The chloride concentration exhibited seasonal variations owing to the use of chloride salts for deicing the roads in the winter months. The chloride concentrations ranged from 92.6 mg/L to 428.7 mg/L. Although none of the samples exceeded the United States Environmental Protection Agency (USEPA) chloride acute level of 860 mg/L, a considerable number (44%) of the chloride values surpassed the USEPA chronic aquatic life criterion of 230 mg/L. The percent relative standard deviation (%RSD) for the students’ individual results ranged from 0.62 to 4.69, with 62% having %RSD below 2.00%. For the unknown aqueous samples, the students’ precision results ranged from 0.24 to 7.80 %RSD, with 59% of the students achieving %RSD < 2.10%. In addition to providing a hands-on milieu for learning the fundamentals of potentiometry with ion-selective electrodes, this experiment highlights the application of this technique to analyze real-world samples obtained from a river that is familiar to the students, since it runs through our campus.