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You can use the DPD (N,N-diethyl-p-phenylenediamine) colorimetric method to measure chlorine concentration using a spectrophotometer.
1. Method:
- DPD Method: DPD reacts with free chlorine to form a colored compound, which can be measured using a spectrophotometer at a specific wavelength. The intensity of the color is directly proportional to the concentration of chlorine.
- Procedure:
- Prepare a standard solution of chlorine using a known concentration of sodium hypochlorite.
- Prepare a series of standard dilutions of the chlorine solution.
- Add a DPD tablet to a sample of your water, and measure the absorbance using the spectrophotometer at the appropriate wavelength.
- Compare the absorbance of your sample to the absorbance of the standards to determine the concentration of chlorine in your sample.
2. DPD Tablets:
- DPD 1: Measures free chlorine (Cl2) only.
- DPD 2: Measures free chlorine (Cl2) and combined chlorine (chloramines).
- DPD 3: Measures total chlorine (free chlorine and combined chlorine) and monochloramine.
Since you're interested in dechlorination, you should use DPD 1 to measure the free chlorine concentration before and after the dechlorination process. The difference between the two measurements will give you the amount of chlorine removed during the process.