Limit of Bromides

Step-by-Step Instructions 
 
 
 Prepare the sample solution as specified. 
 
 
 Add pH 4.7 phenol red TS and chloramine T solution. 
 
 
 Mix immediately and wait exactly 2 minutes. 
 
 
 Add sodium thiosulfate to stop the reaction. 
 
 
 Measure the absorbance at 590 nm using UV-Vis spectroscopy. 
 
 
 Compare the absorbance against a standard solution containing 3 µg/mL of potassium bromide. 
 
 
 Acceptance Criteria 
 
 
 The absorbance of the Sample solution is not greater than that of the Standard solution (NMT 100 ppm). 
 
 
 Tips and Cautions 
 
 
 Starch Preparation: Starch indicator must be "iodide-free" to prevent false positives. 
 
 
 Timing: The Bromide reaction is time-sensitive; exactly 2 minutes must be observed before stopping the reaction with thiosulfate. 
 
 
 Natural Light: Observations for color changes in the Iodide test should be done in natural light for accuracy.