Limit of Bromides

Step-by-Step Instructions

1. Prepare the sample solution as specified.

2. Add pH 4.7 phenol red TS and chloramine T solution.

3. Mix immediately and wait exactly 2 minutes.

4. Add sodium thiosulfate to stop the reaction.

5. Measure the absorbance at 590 nm using UV-Vis spectroscopy.

6. 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.